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7/29/2019 Lecture 4. Refrigerants
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1
Refrigerants
Lecture 4
Refrigeration and Air-conditioning
(MEng 4711)
Technology CollegeMechanical Engineering
Department
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Introduction
Thursday, March 14, 20132
Any body or susbstance that acts as a cooling medium by
extracting heat from another body or substance.
In a closed cycle systems, refrigerant is any working fluid
that undergoes cyclic changes during system operation.
A refrigerant is a substance that picks up latent heat when
the substance evaporates from a liquid to a gas. This is
done at a low temperature and pressure.
A refrigerant expels latent heat when it condenses from a
gas to a liquid at a high pressure and temperature. The
refrigerant cools by absorbing heat in one place anddischarging it in another area.
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Introduction
Thursday, March 14, 20133
Properties of an ideal refrigerantA high latent heat of vaporization
Non-toxic, non-flammable and non-corrosive
Compatible with component materials
Not mix with oil since compressors are lubricated.
Operate at moderate pressures to reduce compressor
work and leakage.
Be relatively cheap to produce and store.
Ease of leak detection
Environmental friendly
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Classification of Refrigerants
Thursday, March 14, 20134
Fluids suitable for refrigeration purposes can be classifiedinto primary and secondary refrigerants.
Primary refrigerants are those fluids which are useddirectly as working fluids, for example in vaporcompression and vapour absorption refrigeration systems.
When used in compression or absorption systems, thesefluids provide refrigeration by undergoing a phase changeprocess in the evaporator.
Secondary refrigerants are those liquids which are used
for transporting thermal energy from one location toanother. Secondary refrigerants are also known under thename brines or antifreezes.
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Thursday, March 14, 20135
If the operating temperatures are above 0oC, then purewater can also be used as secondary refrigerant, for
example in large air conditioning systems.
Antifreezes or brines are used when refrigeration is
required at sub-zero temperatures. Unlike primary refrigerants, the secondary refrigerants do
not undergo phase change as they transport energy from
one location to another.
The commonly used secondary refrigerants are thesolutions of water and ethylene glycol, propylene glycol or
calcium chloride. These solutions are known under the
general name of brines.
Classification of Refrigerants
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Thursday, March 14, 20136
The primary refrigerants are further classified into the following four
groups: Halo-carbon Refrigerants
Azeotropic and Zeotropic Refrigerants
Inorganic Refrigerants and
Hydro-carbon Refrigerants
Halo-carbon refrigerants: The American Society of Heating,
Refrigeration and Air-conditioning Engineers (ASHRAE) identifies 42
halo-carbon compounds as refrigerants, but only a few of them are
commonly used for e.g. R-12,R-22, R-114 etc.
Azeotropic Refrigerants: The term 'azeotrope' refers to a stable
mixture of refrigerants whose vapour and liquid phases retain identical
compositions over a wide range of temperatures. However, these
mixtures usually have properties that differ from either of their
components. The example of Azeotrope Refrigerants are R-500 (73.8%
R-12 & 26.2% R-152), R-502, R-152 etc.
Classification of Refrigerants
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Azeotropic Refrigerants
A stable mixture of two or several refrigerants whose
vapour and liquid phases retain identical compositions over
a wide range of temperatures.
Examples : R-500 : 73.8% R12 and 26.2% R152
R-502 : 8.8% R22 and 51.2% R115
R-503 : 40.1% R23 and 59.9% R13
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Zeotropic Refrigerants
A zeotropic mixture is one whose composition in liquidphase differs to that in vapour phase. Zeotropic refrigerants
therefore do not boil at constant temperatures unlike
azeotropic refrigerants.
Examples: R404a : R125/143a/134a (44%,52%,4%)R407c : R32/125/134a (23%, 25%, 52%)
R410a : R32/125 (50%, 50%)
R413a : R600a/218/134a (3%, 9%, 88%)
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Thursday, March 14, 20139
Inorganic Refrigerants: The inorganic refrigerants wereexclusively used before the introduction of halocarbon
refrigerants. These refrigerants are still in use due to their
inherent thermodynamic and physical properties; for
example Ammonia R-717, Air R-729, CO2 R-744 etc. Hydro-carbon refrigerants: Most of the hydro-carbon
refrigerants are successfully used in industrial and
commercial installations. They possess satisfactory
thermodynamic properties but are highly flammable and
explosive e.g. Ethane R-170,Propane R-290,Propylene R-
1270 etc.
Classification of Refrigerants
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CFC Refrigerants
Thursday, March 14, 201310
The first halogen-based refrigerants (fluorinated
hydrocarbons) were developed over sixty years ago
These refrigerants are composed of chlorine, fluorine, and
carbon, and are called chlorofluorocarbons (CFCs).
These refrigerants are low in toxicity, noncorrosive, andcompatible with other materials. They are not flammable or
explosive with, but sizable quantities must not be released
where there is a flame or electric heating element. They are
particularly harmful to the respiratory system.
Common CFC refrigerants include R-11, R -12, R -113,R -
114,R -115, R-500, R-502, and R-503.
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Thursday, March 14, 201311
R-500, R-502, and R-503 are azeotropic mixtures but are
classified as CFCS by the American Society of Heating,
Refrigeration, and Air Conditioning Engineers (ASHRAE).
CFCs are thought to be one of the major causes of ozone
depletion. By international agreement, they have not been
manufactured since 1995. However, they are still widely
used in existing residential units
CFC Refrigerants
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HCFC Refrigerants
Thursday, March 14, 201312
Hydrochlorofluorocarbons (HCFCS) are moleculescomposed of methane or ethane in combination with a
halogen. This makes up a new molecule that is considered
to be partially halogenated.
The HCFCs have shorter lives and cause less ozonedepletion than the fully halogenated CFCS. Therefore,
they have reduced potential for global warming.
HCFCS such as R-22 and R-123 are considered to be
interim refrigerants. They will be used until suitable
replacements are available.
The EPA requires the phase out of HCFCs by the year
2030.
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HFC Refrigerants
Thursday, March 14, 201313
Hydrofluorocarbons (HFCs) include suchrefrigerants as R-134a and R-23.
They are different from chlorofluorocarbons-they
contain one or more hydrogen atoms and no
chlorine atoms.
HFCS are considered to have zero potential for
ozone depletion.
They have only a slight effect on global warming.
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Refrigerant Blends(Azeotropic- Zeotropic)
Thursday, March 14, 201314
Another more recent category is that of refrigerant blends,commonly referred to as "azeotopic" and "zeotropic."
The use of refrigerant blends is increasing. Azeotropic
blends do not change or separate in composition when
used in Refrigeration systems. Zeotropic refrigerants are also blends composed of various
refrigerants. when used in a refrigeration system, their
volumetric composition and saturation temperature do not
change.
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Refrigerant Selection Criteria
Thursday, March 14, 201315
In order to select the a correct refrigerant, it isnecessary that it should satisfy those properties
which make it ideal to be used for a particular
application. The considered properties are:
Thermodynamic properties,
Chemical properties,
Physical properties
Environmental and safety properties/concerns &Cost
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Refrigerant development
Thursday, March 14, 201316
Refrigerant development can be devided into three
phases:1. Early refrigerants (prior to CFCs)
2. Chloro-fluoro-carbon (CFC) based refrigerants
3. Refrigerants afterMontreal protocol
1. Early Refrigerants
Ethyl etheris the first refrigerant to be used by Jacob Perkinsin 1835.
Ether is liquid at ambient conditions
Ether boiling point is 34C0 at 1atm: for low temperatueconditions, the evaporatorshould work at vacuum.
Possibility forleakage and explosive mix Ether is toxic
Alexander Twinning proposed the use of ammonia and CO2 in1850.
Ammonia is important refrigerant in todays applications
It has good thermal properties, easily available,inexpensive, easy to handle
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Charles Tellier used dimethyl ether as refrigerant in 1864.
it is toxic Raoul Pictet used SO2as refrigerant in 1874.
It is not flammable: it is flame detergent.
Acts as auto-lubricant!
In the presence of water, it forms acid which is toxic and corrosive to
the system.
Linde builed a system based on NH3as refrigerant in 1877.
Imporant land mark in refrigerant development!
Excellent thermodynmic and thermophysical property!
But is toxic, strong smell and slightly flammable
Windhausen used CO2as refrigerant in 1885.
Non toxic and non flamable thus safe!
Imporant application in marine refrigeration and air conditioning.
It needs high operating pressure.
Thursday, March 14, 201317
Refrigerant development
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Problems with Early Refrigerants Toxicity (eg. Ethers, Ammonia)
Flammability (eg. Hydrocarbons)
Material compatibility (eg. Ammonia)
Chemical stability (eg. SO2)
Operating Pressure (eg. CO2)
Limited temperature range (eg. All)
Developments of refrigerants which are non-toxic,
non-flamable, material compatible, chemicallystable!!
Chloro-Flouro-Carbon (CFCs) refrigerants invented!!!Thursday, March 14, 201318
Refrigerant development
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Chloro-fluoro-carbon (CFC) based refrigerants
Thomas midgley and his associates take up the task of
developing refrigerants that are free from problems associated
with early refrigerants in 1928 in USA.
CFCs are synthesized by replacement
hydrocarbons!!
Hydrocarbon
A series of refrigerant family are formed!!!Thursday, March 14, 201319
Refrigerant development
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Chloro-fluoro-carbon (CFC) based refrigerants
CFCs in the trade name ofFREONS enter themarket in 1930s!!
Freon-12 (CCl2F2) is introduced in 1931 and widelyused in domestic refrigeration!!!
Freon-11 (CCl3F) is introduced in 1932 and widelyused in air conditioning in large plants!!!
Freon-22 (CHClF3) and other CFCs aredeveloped!!!
A numbering system is developed for identifyingthe different drived refrigerants!
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Refrigerant development
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Early refrigerants vs. CFCs
Compared to the early refrigeratnts, CFCs havesolved the previous problems!!!
non-toxic
Non-flammable
Chemically stable
Compatable with common materials
Avaialble for a wide refrigeration temperature
Becuase of the favorable properties, CFC refrigeratntsbecame popular and get extensive application!!
Thursday, March 14, 201321
Refrigerant development
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IMPACT OF CFCs
All early refrigerants except ammonia are replacedby various CFCs!
Rapid growth in refrigeration due to the widespreaduse of CFCs!
Refrigeration enters Households in the form ofdomestic refrigerators and air conditioners, thanks
to CFCs! Production and consumption of CFCs increased
exponentially!!
Thursday, March 14, 201322
Refrigerant development
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Ozone layer depletion
Ozone is imporant to protect life on earth from UV radiation.
UV is harmful to life on earth!
Ozone layer depletion consequences
For human beings, increased instances of :
Skin cancer
Weakened immune systems
Damages DNA structure
cataracts
Adverse effect on crop yield
Adverse effects on terrestrial and aquatic ecosystem
Thursday, March 14, 201324
Refrigerant development
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Ozone layer depletion
In 1974, Rowland and Molina propose thetheory ofOzone Layer Depletion due to CFCs
released into atmosphere!
Subsequent studies show Ozone depletingpotential (ODPs) of CFCs and related
substances!
o R-11 (CFCl3) as a reference! =1ODP
o Example: R-12 = 1 ODPo R-114 = 0.8 ODP
o R-22 = 0.055 ODP
Thursday, March 14, 201325
Refrigerant development
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CFCs and Global Warming
CFCs act as greenhouse gases and hence contributesignificantly to Global warming!
Atmoshperic blanket keeps the earth warm and this is essential
for life on earth!
The atmoshperic blancket consists of several gases
(greenhouse gases) such as CO2 N2, H2O!!
Thursday, March 14, 201326
Refrigerant development
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CFCs and Global Warming
Solar radiation mainly consists of long and shortwave radiation.
Atmoshperic blanket with greenhouse gases allows
short wave radiation to pass and reach the earth,
while absorbing the long wave radiations. The earth surface absorbs these shortwave
radiations and keep warm!
The earth also emmits long wave radiations and
these are absorbed at the atmoshpere (by thegreenhouse gases)!!
absorb longwave radiation and transmit short wave
radiations!!
The earth is kept warm!! Without GHG: T = -Thursday, March 14, 201327
Refrigerant development
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CFCs and Global Warming
The temperature condition in the atmoshpere with
out any additives is balanced for this situation!
With the presence of large scale CFCs, the balance
of global warming is disturbed!
CFCs are capable of absorbing much more long
wave radiations compared to the conventional
greenhouse gases such as CO2!!
Global temperature increase!!
Thursday, March 14, 201328
Refrigerant development
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Refrigerants after Montreal protocol
(3rd generation of refrigerants)
Replacements for CFCs should be:
Non-ozone depleting
Have as low GWP as possible
Several Synthetic and natural refrigerants are found toreplace CFCs
Some of the early refrigerants such as CO2 make a
comeback!
CFCs and Replacements
Thursday, March 14, 201330
Refrigerant development
Application CFCs
Domestic refrigerators CFC 12 HFC 134a, HCs
Air conditioning CFC 11, CFC 12, HCFC22
HFC 134a, HCs, CO2, and mixtures
Cold storages HCFC 22, R 502 Ammonia, HFC mixtures
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Designation of refrigerants
Thursday, March 14, 201331
Before the invention of chlorofluorocarbons (CFCs),
refrigerants were called by their chemical names. Because of the complexity of these names, especially the
CFCs the fully halogenated CFCs, and
hydrochlorofluorocarbons (HCFCs), the not fully
halogenated HCFCs, a numbering system was developed forhydrocarbons and halocarbons and is used widely in the
refrigeration industry.
From the number one can get some useful information about
the type of refrigerant, its chemical composition, molecularweight etc.
The refrigerants are internationally designated as 'R'
followed by certain numbers such as R-11, R-12, R-114 etc.
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Thursday, March 14, 201334
Inorganic refrigerants
These are designated by number 7 followed by the
molecular weight of the refrigerant (rounded-off).
Examples:
Ammonia: Molecular weight is 17, the designation is R 717 Carbon dioxide: Molecular weight is 44, the designation is
R744
Water: Molecular weight is 18, the designation is R 718
Designation of refrigerants
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Thursday, March 14, 201335
Mixtures
Azeotropic mixtures are designated by 500 series, whereaszeotropic refrigerants (e.g. non-azeotropic mixtures) are
designated by 400 series.
Examples
R500, R502, R503, R404A, R407A
Designation of refrigerants
Hydrocarbons
Propane (C3H8) : R290
n-butane (C4H10) : R600
iso-butane (C4H10) : R600a
Unsaturated Hydrocarbons: R1150 (C2H4)
R1270 (C3H6)
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Seminar Assignment
Thursday, March 14, 201336
Major Equipment of Vapor-Compression RefrigerationSystems:
Group 1: Compressors
Group 2: Condensers
Group 3: EvaporatorsGroup 4: Expansion Devices (Flow Control Devices)
Assessment (10%)
Report (5%)
Presentation (5%)
Report and presentation should include Types, Principle of
operation, Performance Analysis.
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Grouping
Thursday March 14 201337
Group 1: (Ecaporator)
1. Yoftahe
2. Redia
3. Tadesse
Group 2: (condeser)
1. Acham
2. Dereje
3. G/Medhin
Group 3: (Compressor)1. Asehafi
2. Andualem
3. Chalachew
Group 4: (Exapansion
Device)
1. Lijalem
2. Zinabu3. Mengestab