Vapor pressure The saturation pressures exerted by vapors which are in equilibrium with their liquid or solid forms. One of the most important physical properties of a liquid, the vapor pressure, enters into many thermodynamic calculations and underlies several methods for the determination of the molecular weights of substances dissolved in liquids. If a liquid is introduced into an evacuated vessel at a given temperature, some of the liquid will vaporize, and the pressure of the vapor will attain a maximum value which is termed the vapor pressure of the liquid at that temperature. Although the quantity of liquid remaining does not diminish thereafter, the process of evaporation does not cease. A dynamic equilibrium is established, in which molecules escape from the liquid phase and return from the vapor phase at equal rates.It is important to make a distinction between the vapor pressure of a liquid, as described above, and the pressure of a vapor. The vapor pressure of a pure liquid is a unique and characteristic property of the liquid and depends only upon the temperature. A gas or vapor may, on the other hand, exert any pressure within reason, depending upon the volume to which it is confined, provided it is not in contact with its liquid phase.vapor pressure, pressure exerted by a vapor that is in equilibrium with its liquid. A liquid standing in a sealed beaker is actually a dynamic system: some molecules of the liquid are evaporating to form vapor and some molecules of vapor are condensing to form liquid. At equilibrium the rates of the two processes are equal and the system appears to be stationary The vapor, like any gas, exerts a pressure, and this pressure at equilibrium is called the vapor pressure. Vapor pressure depends on various factors, the most important of which is the nature of the liquid. If the molecules of liquid bind to each other very strongly, there will be less tendency for the molecules to escape as gas and a consequent lower vapor pressure; for example, polar molecules that can form hydrogen bonds between themselves, e.g., water molecules and the alcohols, have relatively low vapor pressures. If there is only weak interaction between the liquid molecules, there will be a greater tendency for the molecules to evaporate and a higher vapor pressure. Temperature also affects the vapor pressure. If the system in equilibrium is perturbed by raising the temperature, then according to Le Châtelier's principle the system should react to relieve this stress; as the temperature is increased, the evaporation process, which absorbs heat, is speeded up to a greater degree than the condensation process, which gives off heat, so that the vapor pressure is higher when equilibrium is restored at the new temperature. If the temperature is increased enough to raise the vapor pressure until it equals atmospheric pressure, the liquid will boil. If the external pressure is reduced, as in a vacuum system, then the liquid will boil much more readily than under atmospheric pressure. This fact is used in the vacuum distillation process to obtain relatively pure samples of liquids with high boiling points. Some solids, e.g., iodine and carbon dioxide, are capable of subliming (going directly from a solid to a gas) at atmospheric pressure and room temperature; thus, such solids also have significant vapor pressures under these conditions. Another factor affecting vapor pressure is the presence of dissolved substances in the liquid or solid; according to Raoult's law, the vapor pressure of a pure liquid or solid is lowered by the addition of a solute.vapor pressure

Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases. All solids and liquids have a tendency to evaporate to a gaseous form, and all gases have a tendency to condense back. At any given temperature, for a particular substance, there is a partial pressure at which the gas of that substance is in dynamic equilibrium with its liquid or solid forms. This is the vapor pressure of that substance at that temperature.In meteorology, the term vapor pressure is used to mean the partial pressure of water vapor in the atmosphere, even if it is not equilibrium, and the equilibrium vapor pressure is specified as such. Meteorologists also use the term saturation vapor pressure to refer to the equilibrium vapor pressure of water or brine above a flat surface, to distinguish it from equilibrium vapor pressure which takes into account the shape and size of water droplets and particulates in the atmosphere.Vapor pressure is an indication of a liquid's evaporation rate. It relates to the tendency of molecules and atoms to escape from a liquid or a solid. A substance with a high vapor pressure at normal temperatures is often referred to as volatile. The higher the vapor pressure of a material at a given temperature, the lower the boiling point.The vapor pressure of any substance increases non-linearly with temperature according to the Clausius-Clapeyron relation. The boiling point of a liquid is the temperature where the vapor pressure equals the ambient atmospheric pressure. At the boiling temperature, the vapor pressure becomes sufficient to overcome atmospheric pressure and lift the liquid to form bubbles inside the bulk of the substance.

Units of vapor pressureThe most common unit for vapor pressure is the torr. 1 torr = 1 mm Hg (one millimeter of mercury). The international unit for pressure is: 1 pascal = a force of 1 newton per square meter = 10 dyn/cm² = 0.01 mbar= 0.0075 mmHg = 0.00000969 atm= 0.00014 psi .

Equilibrium vapor pressure of solidsEquilibrium vapor pressure can be defined as the pressure reached when a condensed phase is in equilibrium with its own vapor. In the case of an equilibrium solid, such as a crystal, this can be defined as the pressure when the rate of sublimation of a solid matches the rate of deposition of its vapor phase. For most solids this pressure is very low, but some notable exceptions are naphthalene, dry ice (the vapor pressure of dry ice is 5.73 MPa (831 psi, 56.5 atm) at 20 degrees Celsius, meaning it will cause most non-ventilated containers to explode if sealed inside), and ice. Ice will still continue to disappear even though the ambient temperature is below the freezing point of water. All solid materials have a vapor pressure. However, due to their often extremely low values, measurement can be rather difficult. Typical techniques include the use of thermogravimetry and gas transpiration.

Relation between solid and liquid vapor pressuresIt may be noted that the vapor pressure of a substance in liquid form is usually different

from the vapor pressure of the same substance in solid form. If the temperature is such that the vapor pressure of the liquid is higher than that of the solid, liquid will vaporize but vapor will condense to a solid, i.e. the liquid is freezing. If the temperature is such that the vapor pressure of the liquid is lower than that of the solid, solid will vaporize but vapor will condense to a liquid, i.e. the solid is melting. At the temperature that equalizes the two vapor pressures, an equilibrium exists between solid and liquid phases. This temperature is referred to as the melting point.

Water vapor pressureGraph of water vapor pressure versus temperature. Note that at the boiling point of 100°C, the vapor pressure equals the standard atmospheric pressure of 760 Torr. Water, like all liquids, starts to boil when its vapor pressure reaches its surrounding pressure. At higher elevations the atmospheric pressure is lower and water will boil at a lower temperature. The boiling temperature of water for pressures around 100 kPa In meteorology, the international standard for the vapour pressure of water over a flat surface is given by the Goff-Gratch equation.

Partial pressuresRaoult's law gives an approximation to the vapor pressure of mixtures of liquids. It states that the activity (pressure or fugacity) of a single-phase mixture is equal to the mole-fraction-weighted sum of the components' vapor pressures:

Failed to parse (unknown function\text): p_\text{tot} = \sum_i p_i\chi_i where p is vapor pressure, i is a component index, and χ is a mole fraction. The term piχi is the vapor pressure of component i in the mixture. Raoult's Law is applicable only to non-electrolytes (uncharged species); it is most appropriate for non-polar molecules with only weak intermolecular attractions (such as London forces).Systems that have vapor pressures higher than indicated by the above formula are said to have positive deviations. Such a deviation suggests weaker intermolecular attraction than in the pure components, so that the molecules can be thought of as being "held in" the liquid phase less strongly than in the pure liquid. An example is the azeotrope of approximately 95% ethanol and water. Because the azeotrope's vapor pressure is higher than predicted by Raoult's law, it boils at a temperature below that of either pure component.There are also systems with negative deviations that have vapor pressures that are lower than expected. Such a deviation is evidence for stronger intermolecular attraction between the constituents of the mixture than exists in the pure components. Thus, the molecules are "held in" the liquid more strongly when a second molecule is present. An example is a mixture of trichloromethane (chloroform) and 2-propanone (acetone), which boils above the boiling point of either pure component.partial pressure In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume.

In chemistry, the partial pressure of a gas in a mixture of gases is defined as above. The partial pressure of a gas dissolved in a liquid is the partial pressure of that gas which would be generated in a gas phase in equilibrium with the liquid at the same temperature. The partial pressure of a gas is a measure of thermodynamic activity of the gas's molecules. Gases will always flow from a region of higher partial pressure to one of lower pressure; the larger this difference, the faster the flow.Vapor pressure is the pressure of a vapor in equilibrium with its non-vapor phases (i.e., liquid or solid). Most often the term is used to describe a liquid's tendency to evaporate. It is a measure of the tendency of molecules and atoms to escape from a liquid or a solid. A liquid's boiling point corresponds to the point where its vapor pressure is equal to the surrounding atmospheric pressure.Gases dissolve, diffuse, and react according to their partial pressures, and not necessarily according to their concentrations in a gas mixture.

Dalton's law of partial pressuresThe pressure of an ideal gas in a mixture is equal to the pressure it would exert if it occupied the same volume alone at the same temperature. This is because ideal gas molecules are so far apart that they don't interfere with each other at all. Actual real-world gases come very close to this ideal.A consequence of this is that the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the individual gases in the mixture as stated by Dalton's law.

Equilibrium constants of reactions involving gas mixturesIt is possible to work out the equilibrium constant for a chemical reaction involving a mixture of gases given the partial pressure of each gas and the overall reaction formula. For reversible reactions, changes in the total pressure, temperature or reactant concentrations will shift the equilibrium so as to favor either the right or left side of the reaction in accordance with Le Chatelier's Principle. However, the reaction kinetics may either oppose or enhance the equilibrium shift. In some cases, the reaction kinetics may be the over-riding factor to consider.

Henry's Law and the solubility of gasesThe form of the equilibrium constant shows that the concentration of a solute gas in a solution is directly proportional to the partial pressure of that gas above the solution. This statement is known as Henry's Law and the equilibrium constant k is quite often referred to as the Henry's Law constant. Henry's Law is an approximation that only applies for dilute, ideal solutions and for solutions where the liquid solvent does not react chemically with the gas being dissolved.

Partial pressure in diving breathing gasesIn recreational diving and professional diving the richness of individual component gases of breathing gases is expressed by partial pressure.

Using diving terms, partial pressure is calculated as:partial pressure = total absolute pressure x volume fraction of gas component

For the component gas "i":ppi = P x Fi

For example, at 50 metres (165 feet), the total absolute pressure is 6 bar (600 kPa) (i.e., 1 bar of atmospheric pressure + 5 bar of water pressure) and the partial pressures of the main components of air, oxygen 21% by volume and nitrogen 79% by volume are:

ppN2 = 6 bar x 0.79 = 4.7 bar absolute ppO2 = 6 bar x 0.21 = 1.3 bar absolute

where:

ppi = partial pressure of gas component i = Pi in the terms used in this article

P = total pressure = P in the terms used in this article

Fi = volume fraction of gas component i = mole fraction, xi, in the terms used in this article

Heat-Transfer Fluids for Solar Water Heating SystemsHeat-transfer fluids carry heat through solar collectors and a heat exchanger to the heat storage tanks in solar water heating systems. When selecting a heat-transfer fluid, you and your solar heating contractor should consider the following criteria:

Coefficient of expansion – the fractional change in length (or sometimes in volume, when specified) of a material for a unit change in temperature

Viscosity – resistance of a liquid to sheer forces (and hence to flow) Thermal capacity – the ability of matter to store heat Freezing point – the temperature below which a liquid turns into a solid Boiling point – the temperature at which a liquid boils Flash point – the lowest temperature at which the vapor above a liquid can be ignited

in air. For example, in a cold climate, solar water heating systems require fluids with low freezing points. Fluids exposed to high temperatures, as in a desert climate, should have a high boiling point. Viscosity and thermal capacity determine the amount of pumping energy required. A fluid with low viscosity and high specific heat is easier to pump, because it is less resistant to flow and transfers more heat. Other properties that help determine the effectiveness of a fluid are its corrosiveness and stability.

Types of Heat-Transfer FluidsThe following are some of the most commonly used heat-transfer fluids and their

properties:

AirAir will not freeze or boil, and is non-corrosive. However, it has a very low heat capacity, and tends to leak out of collectors, ducts, and dampers.

WaterWater is nontoxic and inexpensive. With a high specific heat, and a very low viscosity, it's easy to pump. Unfortunately, water has a relatively low boiling point and a high freezing point. It can also be corrosive if the pH (acidity/alkalinity level) is not maintained at a neutral level. Water with a high mineral content (i.e., "hard" water) can cause mineral deposits to form in collector tubing and system plumbing.

Glycol/water mixturesGlycol/water mixtures have a 50/50 or 60/40 glycol-to-water ratio. Ethylene and propylene glycol are "antifreezes." Ethylene glycol is extremely toxic and should only be used in a double-walled, closed-loop system. You can use food-grade propylene glycol/water mixtures in a single-walled heat exchanger, as long as the mixture has been certified as nontoxic. Make sure that no toxic dyes or inhibitors have been added to it. Most glycols deteriorate at very high temperatures. You must check the pH value, freezing point, and concentration of inhibitors annually to determine whether the mixture needs any adjustments or replacements to maintain its stability and effectiveness.

Hydrocarbon oilsHydrocarbon oils have a higher viscosity and lower specific heat than water. They require more energy to pump. These oils are relatively inexpensive and have a low freezing point. The basic categories of hydrocarbon oils are synthetic hydrocarbons, paraffin hydrocarbons, and aromatic refined mineral oils. Synthetic hydrocarbons are relatively nontoxic and require little maintenance. Paraffin hydrocarbons have a wider temperature range between freezing and boiling points than water, but they are toxic and require a double-walled, closed-loop heat exchanger. Aromatic oils are the least viscous of the hydrocarbon oils.

Refrigerants/phase change fluidsThese are commonly used as the heat transfer fluid in refrigerators, air conditioners, and heat pumps. They generally have a low boiling point and a high heat capacity. This enables a small amount of the refrigerant to transfer a large amount of heat very efficiently. Refrigerants respond quickly to solar heat, making them more effective on cloudy days than other transfer fluids. Heat absorption occurs when the refrigerant boils (changes phase from liquid to gas) in the solar collector. Release of the collected heat takes place when the now-gaseous refrigerant condenses to a liquid again in a heat exchanger or condenser. For years chlorofluorocarbon (CFC) refrigerants, such as Freon, were the primary fluids used by refrigerator, air-conditioner, and heat pump manufacturers because they are nonflammable, low in toxicity, stable, noncorrosive, and do not freeze.

However, due the negative effect that CFCs have on the earth's ozone layer, CFC production is being phased out, as is the production of hydrochlorofluorocarbons (HCFC). The few companies that produced refrigerant-charged solar systems have either stopped manufacturing the systems entirely, or are currently seeking alternative refrigerants. Some companies have investigated methyl alcohol as a replacement for refrigerants.If you currently own a refrigerant-charged solar system and it needs servicing, you should contact your local solar or refrigeration service professional. Since July 1, 1992, intentional venting of CFCs and HCFCs during service and maintenance or disposal of the equipment containing these compounds is illegal and punishable by stiff fines. Although production of CFCs ceased in the U.S. 1996, a licensed refrigeration technician can still service your system. You may wish to contact your service professional to discuss the possible replacement of the CFC refrigerant with methyl alcohol or some other heat transfer fluid.Ammonia can also be used as a refrigerant. It's commonly used in industrial applications. Due to safety considerations it's not used in residential systems. The refrigerants can be aqueous ammonia or a calcium chloride ammonia mixture.

SiliconesSilicones have a very low freezing point, and a very high boiling point. They are noncorrosive and long-lasting. Because silicones have a high viscosity and low heat capacities, they require more energy to pump. Silicones also leak easily, even through microscopic holes in a solar loop.

Freezing Point The freezing point of a pure (unmixed) liquid is essentially the same as the melting point of the same substance in its solid form and may be regarded as the temperature at which the solid and liquid states of the substance are in equilibrium. If heat is applied to a mixture of liquid and solid substance at its freezing point, the temperature of the substance remains constant until it has become completely liquefied, because the heat is absorbed not in warming the substance but in providing the latent heat of fusion. Similarly, if heat is abstracted from a mixture of liquid and solid substance at its freezing point, the substance will remain at the same temperature until it has become completely solid, because heat is given off by the substance in its change from the liquid to the solid state. Hence, the freezing point or melting point of a pure substance may also be defined as the temperature at which freezing or melting continues once it has commenced. All solids melt when heated to their melting points, but most liquids can remain liquid even though cooled below their freezing points. A liquid may remain in this super cooled state for some time. This phenomenon is explained by molecular theory, which conceives the molecules of a solid as being well ordered and the molecules of a liquid as being disordered. To solidify, a liquid must have a nucleus (a point of molecular orderliness) around which the disordered molecules can crystallize. The formation of a nucleus is a matter of chance, but once a nucleus forms, the super cooled liquid will solidify rapidly. The freezing point of a solution is lower than the freezing point of the pure solvent before introduction of the solute (substance dissolved). The amount that the freezing point is lowered depends on the molecular concentration of the solute and on whether the solution

is an electrolyte. Nonelectrolytic solutions have higher freezing points for a given concentration of solute than do electrolytes. The molecular weight of an unknown or unidentified substance may be determined by measuring the amount by which the freezing point of a solvent is lowered when a known amount of the unidentified substance is dissolved in it. This process of determining molecular weights is called cryoscopy. In mixed substances and alloys, the freezing point of the mixture may be much lower than the freezing points of any of its individual components. The freezing point of most substances is increased by increase of pressure. In substances, however, that expand on freezing (for example, water) pressure lowers the freezing point. An example of this effect can be observed if a heavy object is placed on a block of ice. The area immediately underneath the object will begin to turn to liquid and will refreeze, without any change in temperature, when the object is removed. This process is known as regulation.Boiling point The boiling point of a liquid is the temperature at which the liquid and vapor phases are in equilibrium with each other at a specified pressure. Therefore, the boiling point is the temperature at which the vapor pressure of the liquid is equal to the applied pressure on the liquid. The boiling point at a pressure of 1 atmosphere is called the normal boiling point.For a pure substance at a particular pressure P, the stable phase is the vapor phase at temperatures immediately above the boiling point and is the liquid phase at temperatures immediately below the boiling point. The liquid-vapor equilibrium line on the phase diagram of a pure substance gives the boiling point as a function of pressure. Alternatively, this line gives the vapor pressure of the liquid as a function of temperature. The vapor pressure of water is 1 atm (101.325 kilopascals) at 100°C (212°F), the normal boiling point of water. The vapor pressure of water is 3.2 kPa (0.031 atm) at 25°C (77°F), so the boiling point of water at 3.2 kPa is 25°C. The liquid-vapor equilibrium line on the phase diagram of a pure substance begins at the triple point (where solid, liquid, and vapor coexist in equilibrium) and ends at the critical point, where the densities of the liquid and vapor phases have become equal. For pressures below the triple-point pressure or above the critical-point pressure, the boiling point is meaningless. Carbon dioxide has a triple-point pressure of 5.11 atm (518 kPa), so carbon dioxide has no normal boiling point. See also Triple point; Vapor pressure.The normal boiling point is high for liquids with strong intermolecular attractions and low for liquids with weak intermolecular attractions. Helium has the lowest normal boiling point, 4.2 K (−268.9°C). Some other normal boiling points are 111.1 K (−162°C) for CH4, 450°C (842°F) for n-C30H62, 1465°C (2669°F) for NaCl, and 5555°C (10031°F) for tungsten.The rate of change of the boiling-point absolute temperature Tb of a pure substance with pressure is given by the equation below. ΔHvap,m is the molar enthalpy (heat) of vaporization, and ΔVvap,m is the molar volume change on vaporization. The quantity ΔHvap,m/Tb is ΔSvap,m, the molar entropy of vaporization. The molar entropy of vaporization at the normal boiling point (nbp) is given approximately by Trouton's rule: ΔSvap,m,nbp ≈ 87 J/mol K (21 cal/mol K). Trouton's rule fails for highly polar liquids (especially hydrogen-bonded liquids). It also fails for liquids boiling at very low or very

high temperatures, because the molar volume of the vapor changes with temperature and the entropy of a gas depends on its volume.When a pure liquid is boiled at fixed pressure, the temperature remains constant until all the liquid has vaporized. When a solution is boiled at fixed pressure, the composition of the vapor usually differs from that of the liquid, and the change in liquid composition during boiling changes the boiling point. Thus the boiling process occurs over a range of temperatures for a solution. An exception is an azeotrope, which is a solution that boils entirely at a constant temperature because the vapor in equilibrium with the solution has the same composition as the solution. In fractional distillation, the variation of boiling point with composition is used to separate liquid mixtures into their components.

Vapor PressureConceptsA phase change may be written as a chemical reaction. The transition from liquid water to steam, , may be written as

H2 (l) .>H2 (g) The equilibrium constant for this reaction (the vaporization reaction) is

K = Pw

where Pw is the partial pressure of the water in the gas phase when the reaction is at equilibrium. This pressure is often called the vapor pressure. The vapor pressure is literally the partial pressure of the compound in the gas.This equilibrium may be established at any temperature. Because vaporization reactions are endothermic, an increase in temperature will shift the equilibrium to the right. Thus at low temperatures the vapor pressure of the liquid is very low and at high temperatures the vapor pressure is quite large.At what temperature will the liquid boil?The boiling point corresponds to the temperature at which the vapor pressure of the liquid equals the atmospheric pressure. If the liquid is open to the atmosphere (that is, not in a sealed vessel), it is not possible to sustain a pressure greater than the atmospheric pressure, because the vapor will simply expand until its pressure equals that of the atmosphere.The temperature at which the vapor pressure exactly equals one atm is called the normal boiling point.In a sealed vessel, where the vapor cannot expand and thus the pressure can build up, it is possible to establish the vaporization equilibrium at temperatures in excess of the normal boiling point.The van't Hoff equation provides a relationship between an equilibrium constant and temperature.

ln K = - ΔHvap

R T+

ΔSvap

R

For this reaction, the equilibrium constant is simply the vapor pressure, P, which when substituted into the above equation yields the Claussius-Clapeyron equation.

ln P = - ΔHvap

R T+

ΔSvap

R

The normal boiling point, Tbpo, corresponds to the temperature at which both the reactant

and the product are in the standard state. A pure liquid under 1 atm pressure is in the standard state. A pure gas at 1 atm pressure is also in the standard state. Thus in the

standard state P = 1 atm. This relation allows the Claussius-Clapeyron equation to be rewritten as

ln P = - ΔHvap

R

1

T

- 1

Tbpo

and

Tbpo =

- ΔHvap

ΔSvap

As these equations illustrate, experiment data for the vapor pressure of a liquid as a function of temperature enables the calculation of both the normal boiling point (or

indeed any boiling point), the standard enthalpy of vaporization, and the standard entropy of vaporization.

chemical formula A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. A chemical formula is also a short way of showing how a chemical reaction occurs. For molecular compounds, it identifies each constituent element by its chemical symbol and indicates the number of atoms of each element found in each discrete molecule of that compound. If a molecule contains more than one atom of a particular element, this quantity is indicated using a subscript after the chemical symbol (although 19th-century books often used superscripts). For ionic compounds and other non-molecular substances, the subscripts indicate the ratio of elements in the empirical formula.

Molecular and structural formulaFor example methane, a simple molecule consisting of one carbon atom bonded to four hydrogen atoms has the chemical formula:

CH4 and glucose with six carbon atoms, twelve hydrogen atoms and six oxygen atoms has the chemical formula:

C6H12O6.

A chemical formula may also supply information about the types and spatial arrangement of bonds in the chemical, though it does not necessarily specify the exact isomer. For example ethane consists of two carbon atoms single-bonded to each other, with each carbon atom having three hydrogen atoms bonded to it. Its chemical formula can be rendered as CH3CH3. If there were a double bond between the carbon atoms (and thus each carbon only had two hydrogens), the chemical formula may be written: CH2CH2, and the fact that there is a double bond between the carbons is assumed. However, a more explicit and correct method is to write H2C:CH2 or H2C=CH2. The two dots or lines indicate that a double bond connects the atoms on either side of them.A triple bond may be expressed with three dots or lines, and if there may be ambiguity, a single dot or line may be used to indicate a single bond.Molecules with multiple functional groups that are the same may be expressed in the following way: (CH3)3CH. However, this implies a different structure from other molecules that can be formed using the same atoms (isomers). The formula (CH3)3CH implies a chain of three carbon atoms, with the middle carbon atom bonded to another carbon: and the remaining bonds on the carbons all leading to hydrogen atoms. However, the same number of atoms (10 hydrogens and 4 carbons, or C4H10) may be used to make a straight chain: CH3CH2CH2CH3.

PolymersFor polymers, parentheses are placed around the repeating unit. For example, a hydrocarbon molecule that is described as: CH3(CH2)50CH3, is a molecule with 50 repeating units. If the number of repeating units is unknown or variable, the letter n may be used to indicate this: CH3(CH2)nCH3.

IonsFor ions, the charge on a particular atom may be denoted with a right-hand superscript. For example Na+, or Cu2+. The total charge on a charged molecule or a polyatomic ion may also be shown in this way. For example: hydronium, H3O+ or sulfate, SO4

2-.

IsotopesAlthough isotopes are more relevant to nuclear chemistry or stable isotope chemistry than to conventional chemistry, different isotopes may be indicated with a left-hand superscript in a chemical formula. For example, the phosphate ion containing radioactive phosphorus-32 is 32PO4

3-. Also a study involving stable isotope ratios might include 18O:16O.A left-hand subscript is sometimes used to indicate redundantly, for convenience, the atomic number.

Empirical formulaIn chemistry, the empirical formula of a chemical is a simple expression of the relative number of each type of atom or ratio of the elements in the compound. Empirical formulas are the standard for ionic compounds, such as CaCl2, and for macromolecules, such as SiO2. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The term empirical refers to the process of elemental analysis, a technique of analytical chemistry used to determine the relative percent composition of a pure chemical substance by element.For example hexane has a molecular formula of C6H14, or structurally CH3CH2CH2CH2CH2CH3, implying that it has a chain structure of 6 carbon atoms, and 14 hydrogen atoms. However, the empirical formula for hexane is C3H7. Likewise the empirical formula for hydrogen peroxide, H2O2, is simply HO expressing the 1:1 ratio of component elements.

specific gravityThe term specific gravity, symbolized sp gr, refers to the ratio of the density of a solid or liquid to the density of water at 4 degrees Celsius. The term can also refer to the ratio of the density of a gas to the density of dry air at standard temperature and pressure, although this specification is less often used. Specific gravity is a dimensionless quantity; that is, it is not expressed in units. To find the sp gr of a solid or liquid, you must know its density in kilograms per meter cubed (kg/m3) or in grams per centimeter cubed (g/cm3). Then, divide this density by the density of pure water in the same units. If you use kg/m3, divide by 1000. If you use g/cm3, divide by 1 (that is, leave the number alone). It is important to use the same units in the numerator and denominator. Water has a specific gravity equal to 1. Materials with a specific gravity less than 1 are less dense than water, and will float on the pure liquid; substances with a specific gravity more than 1 are more dense than water, and will sink. An object with a density of 85 kg/m3 has a specific gravity of 0.085, and will float high on the surface of a body of water. An object with a density of 85 g/cm3 has a specific gravity of 85, and will sink rapidly. To find the specific gravity of a gas, you must know its density in kilograms per meter cubed (kg/m3). Then, divide this density by the density of dry air at standard temperature and pressure. This value is approximately 1.29 kg/m3. Gases with a specific gravity less than 1 will rise in the atmosphere at sea level; gases with a specific gravity greater than 1 will sink and seek regions of low elevation at the earth's surface. Also see kilogram, meter, density In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as:

where, in SI units:ρ (rho) is the density of the substance, measured in kg·m-3

m is the mass of the substance, measured in kg V is the volume of the substance, measured in m3

Measurement of densityFor a homogeneous object, the formula Mass/Volume may be used. The mass is normally measured with an appropriate scale; the volume may be measured directly (from the geometry of the object) or by the displacement of a liquid. A very common instrument for the direct measurement of the density of a liquid is the hydrometer. A less common device for measuring fluid density is a pycnometer, a similar device for measuring the absolute density of a solid is a gas pycnometer.The density of a solid material can be ambiguous, depending on exactly how it is defined, and this may cause confusion in measurement. A common example is sand: if gently filled into a container, the density will be small; when the same sand is compacted into the same container, it will occupy less volume and consequently carry a greater density. This is because "sand" contains a lot of air space in between individual grains; this overall density is called the bulk density, which differs significantly from the density of an individual grain of sand.

Changes of densityIn general density can be changed by changing either the pressure or the temperature. Increasing the pressure will always increase the density of a material. Increasing the temperature generally decreases the density, but there are notable exceptions to this generalisation. For example, the density of water increases between its melting point at 0 °C and 4 °C and similar behaviour is observed in silicon at low temperatures.The effect of pressure and temperature on the densities of liquids and solids is small so that a typical compressibility for a liquid or solid is 10-6 bar-1 (1 bar=0.1 MPa) and a typical thermal expansivity is 10-5 K-1.In contrast, the density of gases is strongly affected by pressure. Boyle's law says that the density of an ideal gas is given bywhere R is the universal gas constant, P is the pressure, m the molar mass, and T the absolute temperature.This means that a gas at 300 K and 1 bar will have its density doubled by increasing the pressure to 2 bar or by reducing the temperature to 150 K.

Density of water

Temperature Density (at 1 atm)

°C °F kg/m³

0.0 32.0 999.8425

4.0 39.2 999.9750

15.0 59.0 999.1026

20.0 68.0 998.2071

Density of air

T in °C ρ in kg/m³ (at 1 atm)

−10 1.341

−5 1.316

0 1.293

5 1.269

10 1.247

15 1.225

20 1.204

25 1.184

30 1.164

DensityDensity is defined as an objects mass per unit volume. Mass is a property.

Mass and Weight - the Difference! - What is weight and what is mass? An explanation of the difference between weight and mass.

The density can be expressed asρ = m / V = 1 / vg (1)whereρ = density (kg/m3)m = mass (kg)V = volume (m3)

vg = specific volume (m3/kg)The SI units for density are kg/m3. The imperial (BG) units are lb/ft3 (slugs/ft3). While people often use pounds per cubic foot as a measure of density in the U.S., pounds are really a measure of force, not mass. Slugs are the correct measure of mass. You can multiply slugs by 32.2 for a rough value in pounds.

Unit converter for other units The higher the density, the tighter the particles are packed inside the substance. Density is a physicalproperty constant at a given temperature and density can help to identify a substance.

Densities and material properties for common materials Example - Use the Density to Identify the Material:An unknown liquid substance has a mass of 18.5 g and occupies a volume of 23.4 ml. (milliliter).The density can be calculated as

ρ = [18.5 (g) / 1000 (g/kg)] / [23.4 (ml) / 1000 (ml/l) 1000 (l/m3) ]= 18.5 10-3 (kg) / 23.4 10-6 (m3)= 790 kg/m3

If we look up densities of some common substances, we can find that ethyl alcohol, or ethanol, has a density of 790 kg/m3. Our unknown liquid may likely be ethyl alcohol!Example - Use Density to Calculate the Mass of a VolumeThe density of titanium is 4507 kg/m3 . Calculate the mass of 0.17 m3 titanium!

m = 0.17 (m3) 4507 (kg/m3) = 766.2 kg

Specific WeightSpecific Weight is defined as weight per unit volume. Weight is a force.

Mass and Weight - the difference! - What is weight and what is mass? An explanation of the difference between weight and mass.

Specific Weight can be expressed asγ = ρ g (2)whereγ = specific weight (kN/m3)ρ = density (kg/m3)g = acceleration of gravity (m/s2)

The SI-units of specific weight are kN/m3. The imperial units are lb/ft3. The local acceleration g is under normal conditions 9.807 m/s2 in SI-units and 32.174 ft/s2 in imperial units.

Example - Specific Weight WaterSpecific weight for water at 60 oF is 62.4 lb/ft3 in imperial units and 9.80 kN/m3 in SI-units.

Specific GravityThe Specific Gravity - SG - is a dimensionless unit defined as the ratio of density of the material to the density of water at a specified temperature. Specific Gravity can be expressed as

SG = = ρ / ρH2O (3)whereSG = specific gravityρ = density of fluid or substance (kg/m3)ρH2O = density of water (kg/m3)

It is common to use the density of water at 4 oC (39oF) as reference - at this point the density of water is at the highest - 1000 kg/m3 or 62.4 lb/ft3.

Thermal Properties of Water Density, Freezing temperature, Boiling temperature, Latent heat of melting, Latent heat of evaporation, Critical temperature ...

Since Specific Weight is dimensionless it has the same value in the metric SI system as in the imperial English system (BG). At the reference point the Specific Gravity has same numerically value as density.Example - Specific GravityIf the density of iron is 7850 kg/m3, 7.85 grams per cubic centimeter (cm3), 7.85 kilograms per liter, or 7.85 metric tons per cubic meter - the specific gravity of iron is:

SG = 7850 kg/m3/ 1000 kg/m3 = 7.85

(the density of water is 1000 kg/m3)The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. Negative work of the same magnitude would be required to return the body to a state of rest from that velocity.

Kinetic energy of systemsFor a single point, or a rigid body that is not rotating, the kinetic energy goes to zero when the body stops.However, for systems containing multiple independently moving bodies, which may exert forces between themselves, and may (or may not) be rotating; this is no longer true.This energy is called 'internal energy'.The kinetic energy of the system at any instant in time is simply the sum of the kinetic energies of the masses- including the kinetic energy due to the rotations.

An example would be the solar system. In the center of mass frame of the solar system, the Sun is (almost) stationary, but the planets and planetoids are in motion about it. Thus even in a stationary center of mass frame, there is still kinetic energy present.However, recalculating the energy from different frames would be tedious, but there is a trick. The kinetic energy of the system from a different inertial frame can be calculated simply from the sum of the kinetic energy in the center of mass frame and adding on the energy that the total mass of bodies in the center of mass frame would have if it were moving at the relative speed between the two frames

Specific Heat The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between heat and temperature change is usually expressed in the form shown below where c is the specific heat. The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change the temperature. The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other common substance. As a result, water plays a very important role in temperature regulation. The specific heat per gram for water is much higher than that for a metal, as described in the water-metal example. For most purposes, it is more meaningful to compare the molar specific heats of substances.

EntropyIn 1854, German physicist Rudolf Clausius defined the second fundamental theorem (the second law of thermodynamics) in the mechanical theory of heat (thermodynamics): "if two transformations which, without necessitating any other permanent change, can mutually replace one another, be called equivalent, then the generations of the quantity of heat Q from work at the temperature T, has the equivalence-value.

In 1865, he came to define this ratio as entropy symbolized by S, such that, for a closed, stationary system:

and thus, by reduction, quantities of heat δQ (an inexact differential) are defined as quantities of TdS (an exact differential):

In other words, the entropy function S facilitates the quantification and measurement of heat flow through a thermodynamic boundary.

DefinitionsIn modern terms, heat is concisely defined as energy in transit. Scottish physicist James Clerk Maxwell, in his 1871 classic Theory of Heat, was one of the first to enunciate a modern definition of “heat”. In short, Maxwell outlined four stipulations on the definition

of heat. One, it is “something which may be transferred from one body to another”, as per the second law of thermodynamics. Two, it can be spoken of as a “measurable quantity”, and this treated mathematically like other measurable quantities. Third, it “can not be treated as a substance”; for it may be transformed into something which is not a substance, e.g. mechanical work. Lastly, it is “one of the forms of energy”. Similar such modern, succinct definitions of heat are as follows:

In a thermodynamic sense, heat is never regarded as being stored within a body. Like work, it exists only as energy in transit from one body to another; in thermodynamic terminology, between a system and its surroundings. When energy in the form of heat is added to a system, it is stored not as heat but as kinetic and potential energy of the atoms and molecules making up the system.

The noun heat is defined only during the process of energy transfer by conduction or radiation.[5]

Heat is defined as any spontaneous flow of energy from one object to another, caused by a difference in temperature between two objects.[6]

Heat may be defined as energy in transit from a high temperature object to a lower temperature object.[7]

Heat is an interaction between two closed systems without exchange of work is a pure heat interaction when the two systems, initially isolated and in a stable equilibrium, are placed in contact. The energy exchanged between the two systems is then called heat.[8]

Heat is a form of energy possessed by a substance by virtue of the vibrational movement, i.e. kinetic energy, of its molecules or atoms.[9]

Heat is the transfer of energy between substances of different temperatures.

Thermodynamics

Internal energyHeat is related to the internal energy U of the system and work W done by the system by the first law of thermodynamics: which means that the energy of the system can change either via work or via heat flows across the boundary of the thermodynamic system. In more detail, Internal energy is the sum of all microscopic forms of energy of a system. It is related to the molecular structure and the degree of molecular activity and may be viewed as the sum of kinetic and potential energies of the molecules; it is comprised of the following types of energies:[10]The transfer of heat to an ideal gas at constant pressure increases the internal energy and

performs boundary work (i.e. allows a control volume of gas to become larger or smaller), provided the volume is not constrained. Returning to the first law equation and separating thework term into two types, "boundary work" and "other" (e.g. shaft work

performed by a

compressor fan), yields the following:This combined quantity ΔU + Wboundary is enthalpy, H, one of the thermodynamic potentials. Both enthalpy, H, and internal energy, U are state functions. State functions return to their initial values upon completion of each cycle in cyclic processes such as that of a heat engine. In contrast, neither Q nor W are properties of a system and need not sum to zero over the steps of a cycle. The infinitesimal expression for heat, δQ, forms an inexact differential for processes involving work. However, for processes involving no change in volume, applied magnetic field, or other external parameters, δQ, forms an exact differential. Likewise, for adiabatic processes (no heat transfer), the expression for work forms an exact differential, but for processes involving transfer of heat it forms an inexact differential.

Heat capacityFor a simple compressible system such as an ideal gas inside a piston, the changes in enthalpy and internal energy can be related to the heat capacity at constant pressure and volume respectively. constrained to have constant volume, the heat, Q, required to change its temperature from an initial temperature, T0, to a final temperature, Tf Removing the volume constraint and allowing the system to expand or contract at constant pressureFor incompressible substances, such as solids and liquids, the distinction between the two types of heat capacity disappears as no work is performed. Heat capacity is an extensive quantity and as such is dependent on the number of molecules in the system. It can be represented as the product of mass, m , and specific heat capacity, or is dependent on the number of moles and the molar heat capacity, according to:

The molar and specific heat capacities are dependent upon the internal degrees of freedom of the system and not on any external properties such as volume and number of molecules.The specific heats of monatomic gases (e.g., helium) are nearly constant with temperature. Diatomic gases such as hydrogen display some temperature dependence, and triatomic gases (e.g., carbon dioxide) still more.In liquids at sufficiently low temperatures, quantum effects become significant. An example is the behavior of bosons such as helium-4. For such substances, the behavior of heat capacity with temperature is discontinuous at the Bose-Einstein condensation point.The quantum behavior of solids is adequately characterized by the Debye model. At temperatures well below the characteristic Debye temperature of a solid lattice, its specific heat will be proportional to the cube of absolute temperature. For low-temperature metals, a second term is needed to account for the behavior of the conduction electrons, an example of Fermi-Dirac statistics.

Changes of phaseThe boiling point of water, at sea level and normal atmospheric pressure and temperature, will always be at nearly 100 °C no matter how much heat is added. The extra heat changes the phase of the water from liquid into water vapor. The heat added to change the phase of a substance in this way is said to be "hidden," and thus it is called latent heat (from the Latin latere meaning "to lie hidden"). Latent heat is the heat per unit mass necessary to change the state of a given substance, andNote that as pressure increases, the L rises slightly. Here, Mo is the amount of mass initially in the new phase, and M is the amount of mass that ends up in the new phase. Also,L generally does not depend on the amount of mass that changes phase, so the equation can normally be written:

Q = LΔm. Sometimes L can be time-dependent if pressure and volume are changing with time, so that the integral can be written as:

Latent heatFrom Wikipedia, the free encyclopediaIn thermochemistry, latent heat is the amount of energy in the form of heat released or absorbed by a substance during a change of phase (i.e. solid, liquid, or gas), - also called a phase transition.The term was introduced around 1750 by Joseph Black as derived from the Latin latere, to lie hidden. The term is now obsolete, replaced by "enthalpy of transformation".Two latent heats (or enthalpies) are typically described: latent heat of fusion (melting), and latent heat of vaporization (boiling). The names describe the direction of heat flow from one phase to the next: solid → liquid → gas.The change is endothermic, i.e. the system absorbs energy, when the change is from solid to liquid to gas. It is exothermic (the process releases energy) when it is in the opposite direction. For example, in the atmosphere, when a molecule of water evaporates from the surface of any body of water, energy is transported by the water molecule into a lower temperature air parcel that contains more water vapor than its surroundings. Because energy is needed to overcome the molecular forces of attraction between water particles, the process of transition from a parcel of water to a parcel of vapor requires the input of energy causing a drop in temperature in its surroundings. If the water vapor condenses back to a liquid or solid phase onto a surface, the latent energy absorbed during evaporation is released as sensible heat onto the surface. The large value of the enthalpy of condensation of water vapor is the reason that steam is a far more effective heating medium than boiling water, and is more hazardous.

Latent Heat EquationThe equation for latent heat is:Q = mLwhere:

Q is the amount of energy required to change the phase of the substance,m is the mass of the substance,L is the specific latent heat for a particular substance.

Phases - Gas, liquid and solidGas, liquid, and solid are known as the three states of matter or material, but each of solid and liquid states may exist in one or more forms. Thus, another term is required to describe the various forms, and the term phase is used. Each distinct form is called a phase, but the concept of phase defined as a homogeneous portion of a system, extends beyond a single material, because a phase may also involve several materials. For example, a homogeneous solution of any number of substances is a one-phase system. Phase is a concept used to explain many physical and chemical changes (reactions). A solid has a definite shape and volume. A liquid has a definite volume but it takes the shape of a container whereas a gas fills the entire volume of a container. You already know that diamond and graphite are solids made up of the element carbon. They are two phases of carbon, but both are solids. Solids are divided into subclasses of amorphous (or glassy) solids and crystalline solids. Arrangements of atoms or molecules in crystalline solids are repeated regularly over a very long range of millions of atoms, but their arrangements in amorphous solids are somewhat random or short range of say some tens or hundreds of atoms. In general, there is only one liquid phase of a material. However, there are two forms of liquid helium, each have some unique properties. Thus, the two forms are different (liquid) phases of helium. At a definite temperature and pressure, the two phases co-exist. So far, all gases behave alike as do mixtures of gases. Thus, a gas is usually considered as a phase.

The Concept of Phase A phase is a distinct and homogeneous state of a system with no visible boundary separating it into parts. Conversion between these states is called a phase transition. Water, H2O, is the most common substance that its gas (steam), liquid (water), and solid (ice) phases are widely known. An ice water mixture has two phases, so are systems containing ice-and-vapour, and water-and-vapour. To recognize the vapour system in these system may require a keen observation, because the vapour usually blends with air, and is not detected directly. You probably also know that several solids may exist for a substance, and each of the solid form is also called a phase. Diamond and graphite being the most quoted examples. Graphite and diamond are both solid carbon. They have different crystal shapes, colors, and structures. They represent two different phases of carbon. Under 1 atm, ice has hexagonal symmetry, while cubic ice is formed under high pressure. In fact, there are at least 8 different types of ice, each being a solid phase. When you mix water and alcohol, regardless of the relative amounts that you use, they

are fully miscible. The resulting mixture has only one phase (a solution). However, water and oil are normally immiscible, and their boundary of separation is visible. They form a two-phase system. Sometimes you cannot "see" the boundary, and you will need scientific reasoning to realize the number of phases present in system. Well, there is so much concept packed into one term that we can not make the definition any simpler for you. However, the term is useful because it can be used to explain many phenomena. There is no substitute for it. Learn it and use it to explain physical changes.

Phase Transitions A state change of any material due to temperature or pressure change is a phase transition. A phase transition is a physical change (or reaction). The following diagram illustrates the key phase transitions: You should know the names of the process for these phase transitions. sublimation deposition SOLID ============> GAS ==============> SOLID

melting freezing SOLID ============> LIQUID =============> SOLID (solidfication)

condensation vaporization GAS =============> LIQUID =============> GAS

OverviewAPI RP 14C, published by the American Petroleum Institute, specifies the requirements for the analysis, design, installation and testing of surface safety systems for offshore production platforms. While the document is a "recommended practice", adherence to its recommendations in U.S. waters is mandated by regulatory requirements. In short, API RP 14C specifies the minimum safety devices to be installed to protect personnel, the environment, and the production facility from threats to safety caused by the production process. As stated in Paragraph 3.2 of API RP 14C, "The release of hydrocarbons is a factor in almost all threats to safety. Thus, the major objective of the safety system should be to prevent the release of hydrocarbons from the process and to minimize the adverse effects of such releases if they occur." The basic premise prescribed by API RP 14C is that the safety system should provide two levels of protection to prevent or minimize the impact of piping or equipment failure that can result in the release of hydrocarbons from the process. The two levels of protection should be independent of and supplemental to devices used for normal process operation, and should be provided by functionally different types of safety devices. Section 4.2 of API RP 14C lists several undesirable events that can occur in the process, along with potential causes, effects, detectable abnormal conditions and

devices typically used to provide primary and secondary protection against the occurrence and escalation of the event. Expanding on the concepts listed in Section 4.2, Appendix A of the document presents a complete safety analysis of each basic process component normally used in an offshore platform production system. For each basic process component (i.e. flow line, pressure vessel, pump, etc), a list of the required safety devices is provided. This list of required safety devices initially considers each component separate from the rest of the process. The Safety Analysis Checklist (SAC) for individual components is then used to justify elimination of safety devices where protection is afforded by virtue of the service conditions or by other redundant devices either upstream or downstream in the process. In this course, the student will review API RP 14C Recommended Practice for Analysis, Design, Installation, and Testing of Basic Surface Safety Systems for Offshore Production Platforms. Note that the API RP 14C document is not provided as part of the purchase price for this course. It must be obtained separately by the student. You will need to purchase a copy of the document using the link provided below: API RP 14C (Seventh Edition)Alternately, you may be able to borrow a copy from your employer or one of your colleagues. Most companies working in the oil & gas sector have at least one copy of API RP 14C in their reference library. Note that the quiz was developed based on the Seventh Edition of API RP 14C (March, 2001). However, the quiz material is backwards compatible to all previous revisions.The student must take a multiple-choice quiz consisting of thirty (30) questions at the end of the course to obtain PDH credits. Specific Knowledge or Skill AttainedThis course teaches the following specific knowledge and skills:

Recommended safety device symbols and equipment identification tags for offshore production platforms

The major objective and premises for the basic analysis and design of an offshore production platform safety system

Undesirable events that can occur in process components, as well as the causes, effects, detectable abnormal conditions, and protection methods associated with each event

Emergency support systems (ESS) used to minimize the effects of escaped hydrocarbons on offshore production platforms, including ESD, fire detection systems, combustible gas detection systems, and containment systems

The methodology used to perform a safety analysis, including Safety Analysis Tables (SAT), Safety Analysis Checklists (SAC) and Safety Analysis Function Evaluation (SAFE) Charts.

Complete safety analysis of each basic process component normally used on an offshore production platform, including wellheads, flow lines, pressure vessels, pumps, heat exchangers, compressors, and pipelines.

Performance testing and reporting procedures for safety devices Hydrogen sulfide gas detection system design criteria

Cyclone SeparatorsDefinition

A cyclone separator is a type of centrifuge designed to separate solid particles or mist from gases or liquid streams within a conical cylinder using centrifugal acceleration. The

centrifugal separating force or acceleration may range from five times gravity in very large diameter, low resistance cyclones to 2500 times gravity in very small, high resistance units ( Perry and Chilton, 1973 ). Mc Cabe et al. ( 1985 ), described the

cyclone as a piece of equipment consisting of a vertical cylinder with a conical bottom with a tangential inlet near the top, and an outlet for removal of the separated fraction at

the bottom of the cone.

Operating PrinciplesThe design principle for a cyclone separator is extremely simple yet unique. The entire

process is driven by the fluid or vapor and the contaminants themselves, coupled with an applied force to pressurize the fluid or vapors. The pressures range from 90 to 140 psi

(Singh and Eckhoff 1995) where the fluid is forced into the separator in liquid hydrocyclones for starch separation

The flow stream enters the body of the separator tangentially through the inlet at the top. The mixture of solids and fluid or vapor begins to swirl due to the circular design of the chamber and continues swirling as it begins to work its way down the funnel until it reaches the bottom. Materials that are denser than the carrier medium are separated from the stream during this downward flow and can be removed through the outlet at the bottom of the cone.

As the mixture is circulating down the funnel it creates a "whirlpool effect" in the middle of the cone. This causes a vortex in the center of the cone through which the lighter flow stream rises.

As the fluid or vapor reaches the top of the vortex, it is passing by the difference in pressure through a tube that sticks down into the center of the funnel. This tube is called a vortex finder. This is needed so that the vortex fluid will not mix with the incoming mixture of fluid and pollutants. The cleaned fluid or vapor is then either expunged into the atmosphere or returned to the system for reuse.

ApplicationsCyclone separators can be used for a variety of purposes including the removal of particulate material from flue gas emissions, dust removal and dried food particle separation from air streams, liquid clarification, the classification of solids based on size or density, and other separation processes. They are inexpensive to construct and operate, and are low in maintenance requirements.

Cyclones have been operated at higher temperatures and pressures than 1000 C and 500 atm respectively. In some cases, when the dust content of the gas shows a high degree of agglomeration or concentration greater than 100 g. / cu. ft., cyclones can remove dusts having a much smaller particle size (Figure 3 and 4). The efficiency may be higher than 98 % for particles between 0.1 and 2.0 micrometers (microns) in size, as a consequence of the predominant effect of agglomeration.In special cases two or more cyclones may be used in series or parallel. Larger particles

(> 100 microns ) are removed in the first unit and finer ones in the second. Batteries of four or more parallel cyclones are very effective in removing fine particles.

According to Farral ( 1976 ), the efficiency of separation of a cyclone unit is dependent upon the product, the cyclone design, the size of the particle to be removed, and its density. A very simple test of the efficiency of a separator in operation may be made by placing a receptacle filled with water on the roof of the building under the outlet of the separator. The receptacle will catch particles of more than 1 micron in diameter.

Sizing and SelectionAccording toGillum (1993 ), the industry standard for air requirements is 3000 cfm. This requirement can seriously inhibit the ability to stack or series cyclone separators for increased cleaning. Because of the flow required, the amount of horsepower needed to generate these flows can be cost prohibitive.

This idea of stacking or series placement of separators and the cost associated brings us back once again to the idea of system design and the importance of proper design. In a recent report, Columbus (1993) showed an increase in the reduction of emissions from cotton gins when a second cyclone was used in series. The cut size of particles removed also decreases with added cyclones (Svarovsky 1984). From 1950s up to now, the LD(large diameter), 2D2D, 1D3D (see Figure 3) and their different treatments have been used in many different kinds of requirements. For the selection of cyclones, the collection efficiency is the main factor considered . The collection efficiency is affected by the particle diameter and velocity of the gas. For example, the 2D2D cyclone collected 100% of particles greater than 20 microns at an optimum inlet velocity of 15.24 m/s (3000 ft./min.); and the particle diameter for 1D3D is 4.5 microns and for LD is 7.7 microns . Using this principle, we can select different cyclones for different usage (Geankoplis, 1978).

emulsionAn emulsion is a mixture of two immiscible (unblendable) substances. One substance (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include butter and margarine, espresso, mayonnaise, semen, the photo-sensitive side of photographic film, and cutting fluid for metalworking. In butter and margarine, a continuous liquid phase surrounds droplets of water (water-in-oil emulsion). Emulsification is the process by which emulsions are prepared.Emulsions tend to have a cloudy appearance, because the many phase interfaces (the boundary between the phases is called the interface) scatter light that passes through the emulsion. Emulsions are unstable and thus do not form spontaneously. Energy input through shaking, stirring, homogenizers, or spray processes are needed to form an emulsion. Over time, emulsions tend to revert to the stable state of oil separated from water. Surface active substances (surfactants) can increase the kinetic stability of emulsions greatly so that, once formed, the emulsion does not change significantly over years of storage. Homemade oil and vinegar salad dressing is an example of an unstable emulsion that will quickly separate unless shaken continuously. This phenomenon is called coalescence, and happens when small droplets recombine to form bigger ones.

Fluid emulsions can also suffer from creaming, the migration of one of the substances to the top of the emulsion under the influence of buoyancy or centripetal force when a centrifuge is used.Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion tends to imply that both the dispersed and the continuous phase are liquid.There are three types of emulsion instability: flocculation, where the particles form clumps; creaming, where the particles concentrate towards the surface (or bottom, depending on the relative density of the two phases) of the mixture while staying separated; and breaking and coalescence where the particles coalesce and form a layer of liquid.

EmulsifierAn emulsifier (also known as an emulgent or surfactant) is a substance which stabilizes an emulsion. Examples of food emulsifiers are egg yolk (where the main emulsifying chemical is the phospholipid lecithin), and mustard, where a variety of chemicals in the mucilage surrounding the seed hull act as emulsifiers; proteins and low-molecular weight emulsifiers are common as well. In some cases, particles can stabilize emulsions as well through a mechanism called Pickering stabilization. Both mayonnaise and hollandaise sauce are oil-in-water emulsions stabilized with egg yolk lecithin. Detergents are another class of surfactant, and will chemically interact with both oil and water, thus stabilising the interface between oil or water droplets in suspension. This principle is exploited in soap to remove grease for the purpose of cleaning. A wide variety of emulsifiers are used in pharmacy to prepare emulsions such as creams and lotions.Whether an emulsion turns into a water-in-oil emulsion or an oil-in-water emulsion depends on the volume fraction of both phases and on the type of emulsifier. Generally, the Bancroft rule applies: emulsifiers and emulsifying particles tend to promote dispersion of the phase in which they do not dissolve very well; for example, proteins dissolve better in water than in oil and so tend to form oil-in-water emulsions (that is they promote the dispersion of oil droplets throughout a continuous phase of water).Emulsion TreatmentThe problemDuring production or refining of oil, emulsions are formed. These emulsions are caused by oil adhering to fine particles or solids. These solids become a portion of the water phase and the natural separation of oil and water does not occur. This emulsion—or cuff layer as if is commonly referred to—requires significant storage and has no value.The solutionEveready’s Deb Scott, aware of the problem, and with input from our customers, designed a system which incorporates the services of several contractors into one single modular, mobile skid unit. This emulsion treatment system features two large disc stack centrifuges, two grit removers, two steam-powered spiral heat exchangers, as well as feed, additive and discharge pumps. The process is extremely efficient at separating liquids so that product can be recovered and waste reduced. In addition to slop oil treatment, it is also effective in cleaning diluents and glycol tanks.

The Eveready advantageThis is a value added process. It means it’s possible for you to recover a sellable product from a waste stream and it reduces the waste in storage tanks or caverns. This innovative approach of treating waste oils is the result of Eveready personnel going the extra mile to provide our customers with efficient and cost-effective solutions to their problems. Our safety commitmentWe have an outstanding safety rating and we strive hard to maintain our safety record. Ourprocess technicians are always supported with comprehensive training on an continuing basis.Wastewater treatment plant Wastewater treatment plant also called wastewater treatment worksSewage treatment – treatment and disposal of human waste. Industrial wastewater treatment – the treatment of wet wastes from manufacturing industry and commerce including mining, quarrying and heavy industries. Agricultural wastewater treatment – treatment and disposal of liquid animal waste, pesticide residues etc. from agriculture. Radioactive waste treatment – the treatment and containment of radioactive waste. Fractionation is a separation process in which a certain quantity of a mixture (solid, liquid, solute or suspension) is divided up in a large number of smaller quantities (fractions) in which the composition changes according to a gradient. Fractions are collected based on differences in a specific property of the individual components. Common trait in fractionations is the need to find an optimum between the amount of fractions collected and the desired purity in each fraction. Fractionation makes it possible to isolate more than two components in a mixture in a single run. This property sets it apart from other separation techniques.Fractionation is widely employed in many branches of science and technology. Mixtures of liquids and gases are separated by fractional distillation by difference in boiling point. Fractionation of components also takes place in column chromatography by a difference in affinity between stationary phase and the mobile phase. In fractional crystallization and fractional freezing chemical substances are fractionated based on difference in solubility at a given temperature. In cell fractionation, cell components are separated by difference in mass.turboexpander A turboexpander, also referred to as a turbo expander, expansion turbine or simply expander, is a centrifugal or axial flow turbine through which a high pressure gas is expanded to produce work that is typically used to drive a compressor. Because work is extracted from the expanding high pressure gas, the expansion is isentropic and the low pressure exhaust gas from the turbine is at a very low temperature, often as low as 200 K (-100 °F) or less.[1] Turbo expanders are very widely used as sources of refrigeration in industrial processes such as: the extraction of ethane as well as natural gas liquids (NGLs) from natural gas[2]; the liquefaction of gases and other low-temperature processes

heat exchanger A heat exchanger is a device built for efficient heat transfer from one fluid to another, whether the fluids are separated by a solid wall so that they never mix, or the fluids are directly contacted. They are widely used in petroleum refineries, chemical plants, petrochemical plants, natural gas processing, refrigeration, power plants, air conditioning and space heating. One common example of a heat exchanger is the radiator in a car, in which a hot engine-cooling fluid, like antifreeze, transfers heat to air flowing through the radiator.

Heat exchangers may be classified according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is most efficient, in that it can transfer the most heat. See countercurrent exchange. In a cross-flow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger.For efficiency, heat exchangers are designed to maximize the surface area of the wall between the two fluids, while minimizing resistance to fluid flow through the exchanger. The exchanger's performance can also be affected by the addition of fins or corrugations in one or both directions, which increase surface area and may channel fluid flow or induce turbulence.The driving temperature across the heat transfer surface varies with position, but an appropriate mean temperature can be defined. In most simple systems this is the log mean temperature difference (LMTD). Sometimes direct knowledge of the LMTD is not available and the NTU method is used.

Types of heat exchangersShell and Tube heat exchangerA typical heat exchanger, usually for higher-pressure applications, is the shell and tube heat exchanger which consists of a series of tubes, through which one of the fluids runs. The second fluid runs over the tubes to be heated or cooled. The set of tubes is called tube bundle, and may be composed by several types of tubes,: plain, logitudinally finned, etc.

Plate heat exchangerAnother type of heat exchanger is the plate heat exchanger. One is composed of multiple, thin, slightly-separated plates that have very large surface areas and fluid flow passages for heat transfer. This stacked-plate arrangement can be more effective, in a given space, than the shell and tube heat exchanger. Advances in gasket and brazing technology have made the plate type heat exchanger increasingly practical. In HVAC applications, large heat exchangers of this type are called plate-and-frame; when used in open loops, these heat exchangers are normally of the gasketed type to allow periodic disassembly, cleaning, and inspection. There are many types of permanently-bonded plate heat

exchangers such as dip-brazed and vacuum-brazed plate varieties, and they are often specified for closed-loop applications such as refrigeration. Plate heat exchangers also differ in the types of plates that are used, and the configurations of those plates. Some plates may be stamped with "chevron" or other patterns, where others may have machined fins and/or grooves.

Regenerative heat exchangerA third type of heat exchanger is the regenerative heat exchanger. In this, the heat from a process is used to warm the fluids to be used in the process, and the same type of fluid is used either side of the heat exchanger. (These heat exchangers can be either plate and frame or shell and tube construction.) Also see: Countercurrent exchange, Regenerator, Economizer

Adiabatic Wheel heat exchangerA fourth type of heat exchanger uses an intermediate fluid or solid store to hold heat, which is then moved to the other side of the heat exchanger to be released. Two examples of this are adiabatic wheels, which consist of a large wheel with fine threads rotating through the hot and cold fluids, and fluid heat exchangers. This type is used when it is acceptable for a small amount of mixing to occur between the two streams.

Fluid heat exchangersThis is a heat exchanger with a gas passing upwards through a shower of fluid (often water), and the water then taken elsewhere before being cooled. This is commonly used for cooling gases whilst also removing certain impurities, thus solving two problems at once. It's widely used in espresso machines as an energy-saving method of cooling super-heated water to be used in the extraction of espresso.

Dynamic Scraped surface heat exchangerAnother type of heat exchanger is called dynamic heat exchanger or scraped surface heat exchanger. This is mainly used for heating or cooling with high viscosity products, crystallization processes, evaporation and high fouling applications. Long running times are achieved due to the continuous scraping of the surface, thus avoiding fouling and achieving a sustainable heat transfer rate during the process.

Phase-change heat exchangersIn addition to heating up or cooling down fluids in just a single phase, heat exchangers can be used either to heat a liquid to evaporate (or boil) it or used as condensers to cool a vapor to condense it back to a liquid. In chemical plants and refineries, reboilers used to heat incoming feed for distillation towers are often heat exchangers. Distillation set-ups typically use condensers to condense distillate vapors back into liquid.Power plants which have steam-driven turbines commonly use heat exchangers to boil

water into steam. Heat exchangers or similar units for producing steam from water are often called boilers. In the nuclear power plants called pressurized water reactors, special large heat exchangers which pass heat from the primary (reactor plant) system to the secondary (steam plant) system, producing steam from water in the process, are called steam generators. All power plants, fossil-fueled and nuclear, using large quantities of steam have large condensers to recycle the water back to liquid form for re-use.In order to conserve energy and cooling capacity in chemical and other plants, regenerative heat exchangers can be used to transfer heat from one stream that needs to be cooled to another stream that needs to be heated, such as distillate cooling and reboiler feed pre-heating.This term can also refer to heat exchangers that contain a material within their structure that has a change of phase. This is usually a solid to liquid phase due to the small volume difference between these states. This change of phase effectively acts as a buffer because it occurs at a constant temperature but still allows for a the heat exchanger to accept additional heat. One example where this has been investigated if for use in high power aircraft electronics.

HVAC air coilsOne of the widest uses of heat exchangers is for air conditioning of buildings and vehicles. This class of heat exchangers is commonly called air coils, or just coils due to their often-serpentine internal tubing. Liquid-to-air, or air-to-liquid HVAC coils are typically of modified crossflow arrangement. In vehicles, heat coils are often called heater cores.On the liquid side of these heat exchangers, the common fluids are water, a water-glycol solution, steam, or a refrigerant. For heating coils, hot water and steam are the most common, and this heated fluid is supplied by boilers, for example. For cooling coils, chilled water and refrigerant are most common. Chilled water is supplied from a chiller that is potentially located very far away, but refrigerant must come from a nearby condensing unit. When a refrigerant is used, the cooling coil is the evaporator in the vapor-compression refrigeration cycle. HVAC coils that use this direct-expansion of refrigerants are commonly called DX coils.On the air side of HVAC coils a significant difference exists between those used for heating, and those for cooling. Due to psychrometrics, air that is cooled often has moisture condensing out of it, except with extremely dry air flows. Heating some air increases that airflow's capacity to hold water. So heating coils need not consider moisture condensation on their air-side, but cooling coils must be adequately designed and selected to handle their particular latent (moisture) as well as the sensible (cooling) loads. The water that is removed is called condensate.For many climates, water or steam HVAC coils can be exposed to freezing conditions. Because water expands upon freezing, these somewhat expensive and difficult to replace thin-walled heat exchangers can easily be damaged or destroyed by just one freeze. As such, freeze protection of coils is a major concern of HVAC designers, installers, and operators.The heat exchangers in direct-combustion furnaces, typical in many residences, are not

'coils'. They are, instead, gas-to-air heat exchangers that are typically made of stamped steel sheet metal. The combustion products pass on one side of these heat exchangers, and air to be conditioned on the other. A cracked heat exchanger is therefore a dangerous situation requiring immediate attention because combustion products are then likely to enter the building.

SelectionDue to the many variables involved, selecting optimal heat exchangers is challenging. Hand calculations are possible, but many iterations are typically needed. As such, heat exchangers are most often selected via computer programs, either by system designers, who are typically engineers, or by equipment vendors.

Heat exchangers in natureHeat exchangers occur naturally in the circulation system of whales. Arteries to the skin carrying warm blood are intertwined with veins from the skin carrying cold blood causing the warm arterial blood to exchange heat with the cold venous blood. This reduces overall heat loss by the whale when diving in cold waters. Wading birds use a similar system to limit heat losses from their body through their legs into the water.In species that have external testes (such as humans), the artery to the testis is surrounded by a mesh of veins called the pampiniform plexus. This cools the blood heading to the testis, while reheating the returning blood.surge tank (engineering) A standpipe or storage reservoir at the downstream end of a closed aqueduct or feeder pipe, as for a water wheel, to absorb sudden rises of pressure and to furnish water quickly during a drop in pressure. Also known as surge drum. An open tank to which the top of a surge pipe is connected so as to avoid loss of water during a pressure surgecirculator pump A circulator pump is a specific type of pump used to circulate gases, liquids, or slurries in a closed circuit. They are commonly found circulating water in a hydronic heating or cooling system. Because they only circulate liquid within a closed circuit, they only need to overcome the friction of a piping system (as opposed to lifting a fluid from a point of lower potential energy to a point of higher potential energy).Circulator pumps as used in hydronic systems are usually electrically powered centrifugal pumps. As used in homes, they are often small, sealed, and rated at a fraction of a horsepower, but in commercial applications they range in size up to many horsepower and the electric motor is usually separated from the pump body by some form of mechanical coupling. The sealed units used in home applications often have the motor rotor, pump impeller, and support bearings combined and sealed within the water circuit. This avoids one of the principal challenges faced by the larger, two-part pumps: maintaining a water-tight seal at the point where the pump drive shaft enters the pump body.

Small- to medium-sized circulator pumps are usually supported entirely by the pipe flanges that join them to the rest of the hydronic plumbing. Large pumps are usually pad-mounted.Pumps that are used solely for closed hydronic systems can be made with cast iron components as the water in the loop will either become de-oxygenated or be treated with chemicals to inhibit corrosion. But pumps that have a steady stream of oxygenated, potable water flowing through them must be made of more expensive materials such as bronze.

Use with domestic hot waterBronze pumps are often used to circulate domestic hot water so that a faucet will provide hot water instantly upon demand. In regions where water conservation issues are rising in importance with a rapidly expanding population, and a record economic expansion that has consumers looking for comfort, so-called Energy-saving Hot Water Recirculation (HWR) pumps can aid in water conservation at a relatively small expense in added energy use. In typical one-way plumbing without a circulation pump, water is simply piped from the water heater through the pipes to the tap. Once the tap is shut off, the water remaining in the pipes cools producing the familiar wait for hot water the next time the tap is opened. By adding a circulator pump and constantly circulating a small amount of hot water through the pipes from the heater to the furthest fixture and back to the heater, the water in the pipes is always hot, and no water is wasted during the wait. The tradeoff is the energy wasted in operating the pump and the heat lost from the constantly-hot pipes. Thermal insulation applied to the pipes helps mitigate this second loss and minimize the amount of water that must be pumped to keep hot water constantly available.The traditional hot water recirculation system uses a dedicated return line from the point of use located farthest from the hot water tank back to the hot water tank. In homes where this return line was not installed the cold water line is used as a return line with a temperature control device closing the connection between the hot and cold lines at a set temperature. Compared to a dedicated return line, using the cold water line as a return has the disadvantage of heating the cold water pipe (and the contained water). Technological advancements within the industry allowed for incorporating timers to limit the operations during specific hours of the day to reduce energy waste by only operating when occupants where likely to use hot water. Additional advancements in technology include pumps which cycle on and off to maintain hot water temperature versus a continuously operating pump which consumes more electrical energy. Utilizing "normally closed" crossover valves have been shown to further reduce energy consumption by preventing undesired siphoning of water from a hot water line during cold water usage which lowers the cold water lines water pressure allowing the higher pressured water in the hot water lines to pass through a "normally open" crossover valve increasing the energy demand on the water heater.How is natural gas made? Background

Natural gas is a mixture of combustible gases formed underground by the decomposition of organic materials in plant and animal. It is usually found in areas where oil is present, although there are several large underground reservoirs of natural gas where there is little or no oil. Natural gas is widely used for heating and cooking, as well as for a variety of industrial applications.Raw MaterialsRaw natural gas is composed of several gases. The main component is methane. Other components include ethane, propane, butane, and many other combustible hydrocarbons. Raw natural gas may also contain water vapor, hydrogen sulfide, carbon dioxide, nitrogen, and helium.During processing, many of these components may be removed. Some—such as ethane, propane, butane, hydrogen sulfide, and helium—may be partially or completely removed to be processed and sold as separate commodities. Other components—such as water vapor, carbon dioxide, and nitrogen—may be removed to improve the quality of the natural gas or to make it easier to move the gas over great distances through pipelines.The resulting processed natural gas contains mostly methane and ethane, although there is no such thing as a "typical" natural gas. Certain other components may be added to the processed gas to give it special qualities. For example, a chemical known as mercaptan is added to give the gas a distinctive odor that warns people of a leak.The Manufacturing ProcessThe methods used to extract, process, transport, store, and distribute natural gas depend on the location and composition of the raw gas and the location and application of the gas by the end users. Here is a typical sequence of operations used to produce natural gas for home heating and cooking use.Extracting

Some underground natural gas reservoirs are under enough internal pressure that the gas can flow up the well and reach Earth's surface without additional help. However, most wells require a pump to bring the gas (and oil, if it is present) to the surface. The most common pump has a long rod attached to a piston deep in the well. The rod is alternately pulled upward and plunged back into the well by a beam that slowly rocks up and down on top of a vertical support. This configuration is often called a horse head pump because the shape of the pulling mechanism on the end of the rocking beam resembles a horse's head.

When the raw natural gas reaches the surface, it is separated from any oil that might be present and is piped to a central gas processing plant nearby. Several hundred wells may all feed into the same plant.

ProcessingAbout 75% of the raw natural gas in the United States comes from underground

reservoirs where little or no oil is present. This gas is easier to process than gas from oil wells. Regardless of the source, most raw natural gas contains dirt, sand, and water vapor, which must be removed before further processing to prevent contamination and corrosion of the equipment and pipelines. The dirt and sand are

removed with filters or traps near the well. The water vapor is usually removed by passing the gas through a tower filled with granules of a solid desiccant, such as alumina or silica gel, or through a liquid desiccant, such as a glycol. After it has been cleaned and dried, the raw gas may be processed further or it may be sent directly to a compressor station and pumped into a main transportation pipeline.

If the raw natural gas contains a large amount of heavier hydrocarbon gases, such as propane and butane, these materials are removed to be sold separately. The most common method is to bubble the raw gas up through a tall, closed tower containing a cold absorption oil, similar to kerosene. As the gas comes in contact with the cold oil, the heavier hydrocarbon gases condense into liquids and are trapped in the oil. The lighter hydrocarbon gases, such as methane and ethane, do not condense into liquid and flow out the top of the tower. About 85% of the propane and almost all of the butane and heavier hydrocarbons are trapped this way. The absorption oil is then distilled to remove the trapped hydrocarbons, which are separated into individual components in a fractionation tower.

At this point, the natural gas contains methane, ethane, and a small amount of propane that wasn't trapped. It may also contain varying amounts of carbon dioxide, hydrogen sulfide, nitrogen, and other materials. A portion of the ethane is sometimes removed to be used as a raw material in various chemical processes. To accomplish this, the water vapor in the gas is further reduced using one of several methods, and the gas is then subjected to repeated compression and expansion cycles to cool the ethane and capture it as a liquid.

Some natural gas contains a high percentage of carbon dioxide and hydrogen sulfide. These chemicals can react with the remaining water vapor in the gas to form an acid, which can cause corrosion. They are removed by flowing the gas up through a tower while a spray of water mixed with a solvent, such as monoethanolamine, is injected at the top. The solvent reacts with the chemicals, and the solution is drained off the bottom of the tower for further processing.

Some natural gas also contains a high percentage of nitrogen. Because nitrogen does not burn, it reduces the heating value of the natural gas. After the carbon dioxide and hydrogen sulfide have been removed, the gas goes through a low-temperature distillation process to liquefy and separate the nitrogen. Together, the processes in steps 6 and 7 are sometimes called "upgrading" the gas because the natural gas is now cleaner and will burn hotter.

If helium gas is to be captured, it is done after the nitrogen is removed. This involves a complex distillation and purification process to isolate the helium from other gases. Natural gas is the primary source of industrial helium in the United States.

TransportingMercaptan is injected into the processed natural gas to give it a distinctive warning

odor, and the gas is piped to a compressor station where the pressure is increased to about 200-1,500 psi (1,380-10,350 kPa). The gas is then transported across country through one of several major pipelines installed underground. These pipelines range from 20 to 42 in (51 to 107 cm) in diameter. About every 100 mi (160 km), another compressor boosts the gas pressure to make up for small

pressure losses caused by friction between the gas and the pipe walls. This keeps the gas flowing.

When the pressurized natural gas reaches the vicinity of its final destination, it is sometimes injected back into the ground for storage. Depleted underground gas and oil reservoirs, porous rock layers known as aquifers, or subterranean salt caverns may be used to store the gas. This ensures a ready supply during the colder winter months.

DistributingWhen gas is needed, it is drawn out of underground storage and is transported

through pipelines at pressures up to 1,000 psi (6,900 kPa). These pipelines bring the gas into the city or area where it is to be used.

The pressure is reduced to below 60 psi (410 kPa), and the gas is distributed in underground pipes that run throughout the area. Before the gas is piped into each house or business, the pressure is further reduced to about 0.25 psi (1.7 kPa).

Quality ControlNatural gas burns readily in air and can explode violently if a large quantity is suddenly ignited. Entire buildings have been leveled by powerful blasts resulting from natural gas leaks. In other cases, people have suffocated in closed rooms that slowly filled with natural gas. Because natural gas is odorless, foul-smelling mercaptan is added to the gas so that even a small leak will be immediately noticeable. To protect high-pressure underground gas pipelines, a bright yellow plastic tape is buried in the ground a few feet above the pipeline to warn people who might be digging in the area. That way, they will uncover the tape before they actually strike the pipeline below. Warning signs are also placed at ground level along the entire length of the pipeline as an additional precaution.Compressor A machine that increases the pressure of a gas or vapor (typically air), or mixture of gases and vapors. The pressure of the fluid is increased by reducing the fluid specific volume during passage of the fluid through the compressor. When compared with centrifugal or axial-flow fans on the basis of discharge pressure, compressors are generally classed as high-pressure and fans as low-pressure machines.Compressors are used to increase the pressure of a wide variety of gases and vapors for a multitude of purposes. A common application is the air compressor used to supply high-pressure air for conveying, paint spraying, tire inflating, cleaning, pneumatic tools, and rock drills. The refrigeration compressor is used to compress the gas formed in the evaporator. Other applications of compressors include chemical processing, gas transmission, gas turbines, and construction. See also Gas turbine; Refrigeration.Compressor displacement is the volume displaced by the compressing element per unit of time and is usually expressed in cubic feet per minute (cfm). Where the fluid being compressed flows in series through more than one separate compressing element (as a cylinder), the displacement of the compressor equals that of the first element. Compressor capacity is the actual quantity of fluid compressed and delivered, expressed in cubic feet per minute at the conditions of total temperature, total pressure, and composition prevailing at the compressor inlet. The capacity is always expressed in terms of air or gas

at intake (ambient) conditions rather than in terms of arbitrarily selected standard conditions.Air compressors often have their displacement and capacity expressed in terms of free air. Free air is air at atmospheric conditions at any specific location. Since the altitude, barometer, and temperature may vary from one location to another, this term does not mean air under uniform or standard conditions. Standard air is at 68°F (20°C), 14.7 lb/in.2

(101.3 kilopascals absolute pressure), and a relative humidity of 36%. Gas industries usually consider 60°F (15.6°C) air as standard.Compressors can be classified as reciprocating, rotary, jet, centrifugal, or axial-flow, depending on the mechanical means used to produce compression of the fluid, or as positive-displacement or dynamic-type, depending on how the mechanical elements act on the fluid to be compressed. Positive-displacement compressors confine successive volumes of fluid within a closed space in which the pressure of the fluid is increased as the volume of the closed space is decreased. Dynamic-type compressors use rotating vanes or impellers to impart velocity and pressure to the fluid.gas compressor A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume. Compression of a gas naturally increases its temperature.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible, so the main action of a pump is to transport liquids.there are many different types of gas compressors. The two primary categories are:

Positive displacement compressors with two sub-categories: Reciprocating Rotary

Dynamic compressors also with two sub-categories: Centrifugal Axial

The more important types in each of the four sub-categories are discussed below.

Centrifugal compressors use a vaned rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants. Their application can be from 100 hp (75 kW) to thousands of horsepower. With multiple staging, they can achieve extremely high output pressures greater than 10,000 psi (69 MPa).Many large snow-making operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression

stage of medium sized gas turbines.Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to the axial direction. The diagonal compressor has a lower diameter diffuser than the equivalent centrifugal compressor.Axial-flow compressors use a series of fan-like rotating rotor blades to progressively compress the gasflow. Stationary stator vanes, located downstream of each rotor, redirect the flow onto the next set of rotor blades. The area of the gas passage diminishes through the compressor to maintain a roughly constant axial Mach number. Axial-flow compressors are normally used in high flow applications, such as medium to large gas turbine engines. They are almost always multi-staged. Beyond about 4:1 design pressure ratio, variable geometry is often used to improve operation.Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors up to 1000 hp are still commonly found in large industrial applications, but their numbers are declining as they are replaced by various other types of compressors. Discharge pressures can range from low pressure to very high pressure (>5000 psi or 35 MPa). In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, and are typically larger, noisier, and more costly than comparable rotary units.[1]Rotary screw compressors use two meshed rotating positive-displacement helical screws to force the gas into a smaller space. These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 hp (2.24 kW) to over 500 hp (375 kW) and from low pressure to very high pressure (>1200 psi or 8.3 MPa). They are commonly seen with roadside repair crews powering air-tools. This type is also used for many automobile engine superchargers because it is easily matched to the induction capacity of a piston engine.A scroll compressor, also known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump or compress fluids such as liquids and gases. The vane geometry may be involute, archimedean spiral, or hybrid curves. They operate more smoothly, quietly, and reliably than other types of compressors.Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid between the scrolls.

A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in touch with the gas being compressed.

Diaphragm compressors are used for hydrogen and compressed natural gas (CNG) as well as in a number of other applications.

MiscellanyAir compressors sold to and used by the general public are often attached on top of a tank for holding the pressurized air. Oil-lubricated and oil-free compressors are available. Oil-free compressors are desirable because without a properly designed separator, oil can make its way into the air stream. In a given use, for example as a diving air compressor, even minimal oil may be unacceptable.

TemperatureCharles's law says "when a gas is compressed, temperature is raised". There are three possible relationships between temperature and pressure in a volume of gas undergoing compression:

Isothermal - gas remains at constant temperature throughout the process. In this cycle, internal energy is removed from the system as heat at the same rate that it is added by the mechanical work of compression. Isothermal compression or expansion is favored by a large heat exchanging surface, a small gas volume, or a long time scale (i.e., a small power level). With practical devices, isothermal compression is usually not attainable. For example, even a bicycle tire-pump gets hot during use.

Adiabatic - In this process there is no heat transfer to or from the system, and all supplied work is added to the internal energy of the gas, resulting in increases of temperature and pressure. Theoretical temperature rise is T2 = T1·Rc

((k-1)/k)), with T1 and T2 in degrees Rankine or kelvins, and k = ratio of specific heats (approximately 1.4 for air). The rise in air and temperature ratio means compression does not follow a simple pressure to volume ratio. This is less efficient, but quick. Adiabatic compression or expansion is favored by good insulation, a large gas volume, or a short time scale (i.e., a high power level). In practice there will always be a certain amount of heat flow, as to make a perfect adiabatic system would require perfect heat insulation of all parts of a machine.

Polytropic - This assumes that heat may enter or leave the system, and that input shaft work can appear as both increased pressure (usually useful work) and increased temperature above adiabatic (usually losses due to cycle efficiency). Cycle efficiency is then the ratio of temperature rise at theoretical 100 percent (adiabatic) vs. actual (polytropic).

Staged compressionSince compression generates heat, the compressed gas is to be cooled between stages making the compression less adiabatic and more isothermal. The inter-stage coolers cause condensation meaning water separators with drain valves are present. The compressor flywheel may drive a cooling fan.For instance in a typical diving compressor, the air is compressed in three stages. If each stage has a compression ratio of 7 to 1, the compressor can output 343 times atmospheric pressure (7 x 7 x 7 = 343 Atmospheres).

Prime moversThere are many options for the "prime mover" or motor which powers the compressor:

gas turbines power the axial and centrifugal flow compressors that are part of jet engines

steam turbines or water turbines are possible for large compressors electric motors are cheap and quiet for static compressors. Small motors suitable for

domestic electrical supplies use single phase alternating current. Larger motors can only be used where an industrial electrical three phase alternating current supply is available.

diesel engines or petrol engines are suitable for portable compressors and support compressors used as superchargers from their own crankshaft power. They use exhaust gas energy to power turbochargers

ApplicationsGas compressors are used in various applications where either higher pressures or lower volumes of gas are needed:

in pipeline transport of purified natural gas to move the gas from the production site to the consumer.

in petroleum refineries, natural gas processing plants, petrochemical and chemical plants, and similar large industrial plants for compressing intermediate and end product gases.

in refrigeration and air conditioner equipment to move heat from one place to another in refrigerant cycles: see Vapor-compression refrigeration.

in gas turbine systems to compress the intake combustion air in storing purified or manufactured gases in a small volume, high pressure cylinders

for medical, welding and other uses. in many various industrial, manufacturing and building processes to power all types

of pneumatic tools. as a medium for transferring energy, such as to power pneumatic equipment. in pressurised aircraft to provide a breathable atmosphere of higher than ambient

pressure. in some types of jet engines (such as turbojets and turbofans) to provide the air

required for combustion of the engine fuel. The power to drive the combustion air compressor comes from the jet's own turbines.

in SCUBA diving, hyperbaric oxygen therapy and other life support devices to store breathing gas in a small volume such as in diving cylinders .

in submarines to store air for later use as buoyancy. in turbochargers and superchargers to increase the performance of internal

combustion engines by concentrating oxygen. in rail and heavy road transport to provide compressed air for operation of rail vehicle

brakes or road vehicle brakes and various other systems (doors, windscreen wipers, engine/gearbox control, etc).

in miscellaneous uses such as providing compressed air for filling pneumatic tires.

Refrigeration System Operating Characteristics GeneralRefrigeration systems must operate at all hours of the year, even when the building is unoccupied. Warmer weather tends to push refrigeration equipment to its capacity limit, thus creating a maximum operating kW and kWh. Evaporators - must be selected to provide the required cooling at all expected ambient conditions even with the maximum frost on the coils (i.e., just prior to defrosting). Evaporator coils used include two types of refrigeration systems: flooded evaporator and direct expansion. For direct expansion systems, two of the most commonly used refrigerant liquid metering devices are the capillary tube and the thermostatic expansion valve. In addition, proper provisions must be made for periodic defrosting of evaporator air-side surfaces. Defrosting may be accomplished using refrigerant compressor discharge hot-gas, water spray, or manually as selected to meet the user's objectives. Suitable drain connections should be provided to carry off the water resulting from defrost operations. Condensers must be selected to operate at all outdoor weather conditions in the area. Air-cooled condensers must be supplied with the proper controls to permit operation at low outdoor ambient conditions. Water-cooled condensers may require water regulating valves to keep condensing pressure high enough to enable the thermal expansion valves to function. The type of condenser selected depends largely on the size of the cooling load,

Refrigeration The cooling of a space or substance below the environmental temperature. Mechanical refrigeration is primarily an application of thermodynamics wherein the cooling medium, or refrigerant, goes through a cycle so that it can be recovered for reuse. The commonly used basic cycles, in order of importance, are vapor-compression, absorption, steam-jet or steam-ejector, and air. Each cycle operates between two pressure levels, and all except the air cycle use a two-phase working medium which alternates cyclically between the liquid and vapor phases.The term “refrigeration” is used to signify cooling below the environmental temperature to lower than about 150 K (−190°F; −123°C). The term “cryogenics” is used to signify cooling to temperatures lower than 150 K. See also Cryogenics.Vapor-compression cycleThe vapor-compression cycle consists of an evaporator in which the liquid refrigerant

boils at low temperature to produce cooling, a compressor to raise the pressure and temperature of the gaseous refrigerant, a condenser in which the refrigerant discharges its heat to the environment, usually a receiver for storing the liquid condensed in the condenser, and an expansion valve through which the liquid expands from the high-pressure level in the condenser to the low-pressure level in the evaporator. This cycle may also be used for heating if the useful energy is taken off at the condenser level instead of at the evaporator level. See also Heat pump.Absorption cycleThe absorption cycle accomplishes compression by using a secondary fluid to absorb the refrigerant gas, which leaves the evaporator at low temperature and pressure. Heat is applied, by means such as steam or gas flame, to distill the refrigerant at high temperature and pressure. The most-used refrigerant in the basic cycle is ammonia; the secondary fluid is then water. This system is used for the lower temperatures. Another system is lithium bromide-water, where the water is used as the refrigerant. This is used for higher temperatures. Due to corrosion, special inhibitors must be used in the lithium bromide-water system. The condenser, receiver, expansion valve, and evaporator are essentially the same as in any vapor-compression cycle. The compressor is replaced by an absorber, generator, pump, heat exchanger, and controlling-pressure reducing valve.

Steam-jet cycleThe steam-jet cycle uses water as the refrigerant. High-velocity steam jets provide a high vacuum in the evaporator, causing the water to boil at low temperature and at the same time compressing the flashed vapor up to the condenser pressure level. Its use is limited to air conditioning and other applications for temperatures above 32°F (0°C).Air cycleThe air cycle, used primarily in airplane air conditioning, differs from the other cycles in that the working fluid, air, remains as a gas throughout the cycle. Air coolers replace the condenser, and the useful cooling effect is obtained by a refrigerator instead of by an evaporator. A compressor is used, but the expansion valve is replaced by an expansion engine or turbine which recovers the work of expansion. Systems may be open or closed. In the closed system, the refrigerant air is completely contained within the piping and components, and is continuously reused. In the open system, the refrigerator is replaced by the space to be cooled, the refrigerant air being expanded directly into the space rather than through a cooling coil.RefrigerantsThe working fluid in a two-phase refrigeration cycle is called a refrigerant. A useful way to classify refrigerants is to divide them into primary and secondary. Primary refrigerants are those fluids (pure substances, azeotropic mixtures which behave physically as a single pure compound, and zeotropes which have temperature glides in the condenser and evaporator) used to directly achieve the cooling effect in cycles where they alternately absorb and reject heat. Secondary refrigerants are heat transfer or heat carrier fluids.

Refrigeration

The cooling of a space or substance below the environmental temperature. Mechanical refrigeration is primarily an application of thermodynamics wherein the cooling medium, or refrigerant, goes through a cycle so that it can be recovered for reuse. The commonly used basic cycles, in order of importance, are vapor-compression, absorption, steam-jet or steam-ejector, and air. Each cycle operates between two pressure levels, and all except the air cycle use a two-phase working medium which alternates cyclically between the liquid and vapor phases.The term “refrigeration” is used to signify cooling below the environmental temperature to lower than about 150 K (−190°F; −123°C). The term “cryogenics” is used to signify cooling to temperatures lower than 150 K. See also Cryogenics.Vapor-compression cycleThe vapor-compression cycle consists of an evaporator in which the liquid refrigerant boils at low temperature to produce cooling, a compressor to raise the pressure and temperature of the gaseous refrigerant, a condenser in which the refrigerant discharges its heat to the environment, usually a receiver for storing the liquid condensed in the condenser, and an expansion valve through which the liquid expands from the high-pressure level in the condenser to the low-pressure level in the evaporator. This cycle may also be used for heating if the useful energy is taken off at the condenser level instead of at the evaporator level. See also Heat pump.Absorption cycleThe absorption cycle accomplishes compression by using a secondary fluid to absorb the

refrigerant gas, which leaves the evaporator at low temperature and pressure. Heat is applied, by means such as steam or gas flame, to distill the refrigerant at high temperature and pressure. The most-used refrigerant in the basic cycle is ammonia; the secondary fluid is then water. This system is used for the lower temperatures. Another system is lithium bromide-water, where the

water is used as the refrigerant. This is used for higher temperatures. Due to corrosion, special inhibitors must be used in the lithium bromide-water system. The condenser, receiver, expansion valve, and evaporator are essentially the same as in any vapor-compression cycle. The compressor is replaced by an absorber, generator, pump, heat exchanger, and controlling-pressure reducing valve.Steam-jet cycleThe steam-jet cycle uses water as the refrigerant. High-velocity steam jets provide a high vacuum in the evaporator, causing the water to boil at low temperature and at the same time compressing the flashed vapor up to the condenser pressure level. Its use is limited to air conditioning and other applications for temperatures above 32°F (0°C).

Air cycleThe air cycle, used primarily in airplane air conditioning, differs from the other cycles in that the working fluid, air, remains as a gas throughout the cycle. Air coolers replace the condenser, and the useful cooling effect is obtained by a refrigerator instead of by an evaporator. A compressor is used, but the expansion valve is replaced by an expansion engine or turbine which recovers the work of expansion. Systems may be open or closed. In the closed system, the refrigerant air is completely contained within the piping and components, and is continuously reused. In the open system, the refrigerator is replaced by the space to be cooled, the refrigerant air being expanded directly into the space rather than through a cooling coil.Refrigerants

The working fluid in a two-phase refrigeration cycle is called a refrigerant. A useful way to classify refrigerants is to divide them into primary and secondary. Primary refrigerants are those

Water-cooled condensers require cooling water from an external cooling tower, or from a lake, well, river or other similar source. Once-through use of city water for condensing purposes is prohibited in most locations. Air-cooled condensers are the most popular since they avoid other problems of water acquisition, treatment and disposal. The trade-off may be higher electrical consumption. As seen here, the evaporative condenser is a combination of a water cooled condenser and an air-cooled condenser that rejects heat through the evaporation of water into an airstream traveling across a condenser coil. Compressors - must be sized to meet the varying needs of each application. Provision must be made to protect the compressor from liquid carry over from the evaporator, in addition to the normal safety controls (high and low pressure cutout. oil pressure, etc.). The most common type of compressor used for commercial refrigeration systems is the reciprocating compressor. Reciprocating compressor types include single-stage (booster or high state), internally compounded, and open, hermetic or semi-hermetic.