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THEORY For molecules of a liquid to evaporate, they must be located near the surface, they have to be

moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase

intermolecular forces.[1] When only a small proportion of the molecules meet these criteria, the rate

of evaporation is lo. !ince the kinetic energy of a molecule is proportional to its temperature,

evaporation proceeds more quickly at higher temperatures. "s the faster-moving molecules escape,

the remaining molecules have loer average kinetic energy, and the temperature of the liquid

decreases. #his phenomenon is also called evaporative cooling. #his is hy

evaporating seat cools the human body. $vaporation also tends to proceed more quickly ith

higher flo rates beteen the gaseous and liquid phase and in liquids ith higher  vapor pressure.

For e%ample, laundry on a clothes line ill dry &by evaporation' more rapidly on a indy day than on

a still day. #hree key parts to evaporation are heat, atmospheric pressure &determines the percent

humidity' and air movement.

(n a molecular level, there is no strict boundary beteen the liquid state and the vapor state.

)nstead, there is a *nudsen layer , here the phase is undetermined. +ecause this layer is only a

fe molecules thick, at a macroscopic scale a clear phase transition interface can be seen.

iquids that do not evaporate visibly at a given temperature in a given gas &e.g., cooking oil at

room temperature' have molecules that do not tend to transfer energy to each other in a pattern

sufficient to frequently give a molecule the heat energy necessary to turn into vapor. oever, these

liquids are evaporating. )t is ust that the process is much sloer and thus significantly less visible.

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EVAPORATIVEEQUILIBRIUM

/apor pressure of ater vs. temperature. 02 #orr  3 1 atm.

)f evaporation takes place in an enclosed area, the escaping molecules accumulate asa vapor  above the liquid. 4any of the moleculesreturn to the liquid, ith returning molecules

becoming more frequent as the density and pressure of the vapor increases. When the process of 

escape and return reaches an equilibrium,[1]  the vapor is said to be 5saturated5, and no further 

change in either vapor pressure and density or liquid temperature ill occur. For a system consisting

of vapor and liquid of a pure substance, this equilibrium state is directly related to the vapor pressure

of the substance, as given by the 6lausius76lapeyron relation8

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here P 1, P 9 are the vapor pressures at temperatures T 1, T 9 respectively, :H vap is the enthalpy of 

vapori;ation, and R  is the universal gas constant. #he rate of evaporation in an open system is

related to the vapor pressure found in a closed system. )f a liquid is heated, hen the vapor 

pressure reaches the ambient pressure the liquid ill boil.

#he ability for a molecule of a liquid to evaporate is based largely on the amount of kinetic

energy an individual particle may possess. $ven at loer temperatures, individual molecules of 

a liquid can evaporate if they have more than the minimum amount of kinetic energy required for 

vapori;ation.

FACTORS INFLUENCING THE

RATE OF EVAPORATION  :-Concentration of the substance evaporating in the air :-

)f the air already has a high concentration of the substance evaporating, then the given

substance ill evaporate more sloly.

 Concentration of other substances in the air :-

)f the air is already saturated ith other substances, it can have a loer capacity for the

substance evaporating.

 Flow rate of air :-

#his is in part related to the concentration points above. )f 5fresh5 air &i.e., air hich is neither 

already saturated ith the substance nor ith other substances' is moving over the

substance all the time, then the concentration of the substance in the air is less likely to go

up ith time, thus encouraging faster evaporation. #his is the result of theboundary layer  at

the evaporation surface decreasing ith flo velocity, decreasing the diffusion distance in

the stagnant layer.

Inter-molecular forces :-

#he stronger the forces keeping the molecules together in the liquid state, the more energy

one must get to escape. #his is characteri;ed by the enthalpy of vapori;ation.

Pressure :-

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$vaporation happens faster if there is less e%ertion on the surface keeping the molecules

from launching themselves.

Surface area :-

 " substance that has a larger surface area ill evaporate faster, as there are more surface

molecules per unit of volume that are potentially able to escape.

Temperature of the substance :-

#he higher the temperature of the substance the greater the kinetic energy of the molecules

at its surface and therefore the faster the rate of their evaporation.

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THERMODYNAMICS$vaporation is an endothermic process, in that heat is absorbed during

evaporation.)n thermodynamics, the term endothermic process describes a process or reaction in

hich the system absorbs energy from its surroundings< usually, but not alays, in the form of heat.

#he term as coined by 4arcellin +erthelot from the =reek roots endo-, derived from the ord 5endon5

& >?@>' meaning 5ithin5 and the root 5therm5 &ABCD-' meaning 5hot.5 #he intended sense is that of aἔ

reaction that depends on absorbing heat if it is to proceed. #he opposite of an endothermic process is

an e%othermic process, one that releases, 5gives out5 energy in the form of &usually, but not alays'

heat. #hus in each term &endothermic E e%othermic' the prefi% refers to here heat goes as the

reaction occurs, though in reality it only refers to here the energy goes, ithout necessarily being inthe form of heat.

  #he concept is frequently applied in physical sciences to, for e%ample, chemical reactions,

here thermal energy &heat' is converted to chemical bond energy.

  $ndothermic &and e%othermic' analysis only accounts for the enthalpy change &' of a

reaction. #he full energy analysis of a reaction is the =ibbs free energy &=', hich includes

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an entropy &!' and temperature term in addition to the enthalpy. " reaction ill be a  spontaneous

process at a certain temperature if the products have a loer =ibbs free energy &an e%ergonic reaction'

even if the enthalpy of the products is higher. $ntropy and enthalpy are different terms, so the change

in entropic energy can overcome an opposite change in enthalpic energy and make an endothermic

reaction favorable.

EXAMPLES :-• Ghotosynthesis

• 4elting ice

• 6racking of alkanes

• /aporising rubbing alcohol

• #hermal decomposition reactions

• Hissolving ammonium chloride in ater 

• igh-energy neutrons can produce tritium from lithium-0 in an endothermic reaction,

consuming 9.I 4e/. #his as discovered hen the 1JKI 6astle +ravo nuclear test produced

an une%pectedly high yield.7

3 Li 

+ n  →4

2 He 

+3

1T

+ n

ATMOMETER

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Figure :- ATMOMETER

 "n atmometer  or evaporimeter  is a scientific instrument used for measuring the rate of ater

evaporation from a et surface to the atmosphere. "tmometers are mainly used by farmers and

groers to measure evapotranspiration &$#' rates of crops at any field location.[1] $vapotranspiration is

a measure of all of the ater that evaporates from land surfaces plus the ater that transpires from

plant surfaces.[9] +ased on the amount of ater that does evaporate and transpire, the user can ater

crops correspondingly, hich results in less ater use and possibly increased crop yields. 6ompanies

that currently sell atmometers include 6E4 4eteorological !upply and 6alsense. "n atmometer

consists of a porous, ceramic plate connected to a ater reservoir by a glass or plastic tube. #hedevice stands around 1.K79 ft &2.I72.1 m' tall ith a diameter of L7I in &07129 mm' #he electronic

model eliminates possible human error that could occur from reading the gauge, but costs

appro%imately MJ22 hile the manual model costs appro%imately ML22.

APPLICATIONS :-  PAGE NO. 23BY:-ROHIT AGRAWAL

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• )ndustrial applications include many printing and coating processes< recovering salts from

solutions< and drying a variety of materials such as lumber, paper, cloth and chemicals.

• #he use of evaporation to dry or concentrate samples is a common preparatory step for

many laboratory analyses such as spectroscopy and chromatography. !ystems used for this

purpose include rotary evaporators and centrifugal evaporators.

• When clothes are hung on a laundry line, even though the ambient temperature is belo the

boiling point of ater, ater evaporates. #his is accelerated by factors such as lo humidity,

heat &from the sun', and ind. )n a clothes dryer , hot air is blon through the clothes, alloing

ater to evaporate very rapidly.

• #he 4atkiN4atka, a traditional )ndian porous clay container used for storing and cooling

ater and other liquids.

• #he botio, a traditional !panish porous clay container designed to cool the contained aterby evaporation.

• $vaporative coolers, hich can significantly cool a building by simply bloing dry air over a

filter saturated ith ater.

COMBUSTION VAPORIZATION :-

Fuel droplets vapori;e as they receive heat by mi%ing ith the hot gases in the combustion chamber.

eat &energy' can also be received by radiation from any hot refractory all of the combustion

chamber.

PRE-COMBUSTION VAPORIZATION :-

)nternal combustion engines rely upon the vapori;ation of the fuel in the cylinders to form a fuelNair

mi%ture in order to burn ell. #he chemically correct airNfuel mi%ture for total burning of gasoline has

been determined to be 1K parts air to one part gasoline or 1KN1 by eight. 6hanging this to a volume

ratio yields O222 parts air to one part gasoline or O,222N1 by volume.

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FILM DEPOSITION :-

#hin films may be deposited by evaporating a substance and condensing it onto a substrate, or by

dissolving the substance in a solvent, spreading the resulting solution thinly over a substrate, and

evaporating the solvent.

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HEATING EFFECT OF

EVAPORATION 

#emperature-dependency of the heats of vapori;ation for ater, methanol,

ben;ene, and acetone.

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#he enthalpy of vaporization, &symbol vap' also knon as the latent! heat of 

vaporization or heat of evaporation, is theenthalpy change required to transform a given quantity

of a substance from a liquid into a gas at a given pressure &oftenatmospheric pressure, as in !#G'.

)t is often measured at the normal boiling point of a substance< although tabulated values are usually

corrected to 9JO *, the correction is often smaller than the uncertainty in the measured value.

#he heat of vapori;ation is temperature-dependent, though a constant heat of vapori;ation can be

assumed for small temperature ranges and for reduced temperature #r PP1.2. #he heat of 

vapori;ation diminishes ith increasing temperature and it vanishes completely at the critical

temperature &#r 31' because above the critical temperature the liquid and vapor  phases no longer 

e%ist, since the substance is a supercritical fluid.

UNITS :-/alues are usually quoted in QNmol or kQNmol &molar enthalpy of vapori;ation', although kQNkg or QNg

&specific heat of vapori;ation', and older units like kcalNmol, calNg and +tuNlb are sometimes still

used, among others.

PHYSICAL MODEL FOR

EVAPORIZATION

 " simple physical model for the liquid7gas phase transformation as proposed in 922J by Qo;sef

=arai.[1] )t is suggested that the energy required to free an atom from the liquid is equivalent to the

energy needed to overcome the surface resistance of the liquid. #he model allos calculating the

latent heat by multiplying the ma%imum surface area covering an atom &Fig. 1' ith the surface

tension and the number of atoms in the liquid. #he calculated latent heat of vapori;ation values for

the investigated IK elements agrees ell ith e%periments. "nother model hich utili;es the data

set from Qo;sef =araiRs model shos that the liquid7gas phase change can be e%plained in terms ofkinetic theory by considering that the energy required for vapori;ation is e%tracted from all si% of the

vapori;ing moleculeRs neighbours. #his includes a required rethink of the probability of vapori;ation,

and has consequences to the 6lausius-6lapeyron equation. 4oreover, it does resolve the issue of

the latent heat of vapori;ation being significantly greater than the thermal energy e%changed

beteen molecules, i.e. at boiling point the latent heat for ater is appro%imately 1L.9

times k# &+olt;mannRs factor multiplied by boiling temperature.' PAGE NO. 23

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ENTHALPY OF

CONDENSATION

#he enthalpy of condensation &or heat of condensation' is by definition equal to the enthalpy of 

vapori;ation ith the opposite sign8 enthalpy changes of vapori;ation are alays positive &heat is

absorbed by the substance', hereas enthalpy changes of condensation are alays negative &heat

is released by the substance'.

THERMODYNAMIC

BACKGROUND :-

#he enthalpy of vapori;ation can be ritten as

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)t is equal to the increased internal energy of the vapor phase compared ith the liquid phase, plus

the ork done against ambient pressure. #he increase in the internal energy can be vieed as the

energy required to overcome theintermolecular interactions  in the liquid &or solid, in the case

of sublimation'. ence helium has a particularly lo enthalpy of vapori;ation, 2.2OIK kQNmol, as

the van der Waals forces beteen helium atoms are particularly eak. (n the other hand,the molecules in liquid ater  are held together by relatively strong hydrogen bonds, and its enthalpy

of vapori;ation, I2.K kQNmol, is more than five times the energy required to heat the same quantity

of ater from 2 S6 to 122 S6 &c p 3 0K.L Q *T1 molT1'. 6are must be taken, hoever, hen using

enthalpies of vapori;ation to measure the strength of intermolecular forces, as these forces may

persist to an e%tent in the gas phase &as is the case ith hydrogen fluoride', and so the calculated

value of the bond strength ill be too lo. #his is particularly true of metals, hich often

form covalently bonded molecules in the gas phase8 in these cases, the enthalpy of 

atomi;ation must be used to obtain a true value of the bond energy.

 "n alternative description is to vie the enthalpy of condensation as the heat hich must be

released to the surroundings to compensate for the drop in entropy hen a gas condenses to a

liquid. "s the liquid and gas are in equilibrium at the boiling point &T b', :vG 3 2, hich leads to8

 "s neither entropy nor enthalpy vary greatly ith temperature, it is normal to use the tabulated

standard values ithout any correction for the difference in temperature from 9JO *. " correction

must be made if the pressure is different from 122 kGa, as the entropy of a gas is proportional to its

pressure &or, more precisely, to its fugacity'8 the entropies of liquids vary little ith pressure, as

the compressibility of a liquid is small.

#hese to definitions are equivalent8 the boiling point is the temperature at hich the increased

entropy of the gas phase overcomes the intermolecular forces. "s a given quantity of matter alays

has a higher entropy in the gas phase than in a condensed phase & is alays positive', and

from

,

the =ibbs free energy change falls ith increasing temperature8 gases are favored at higher

temperatures, as is observed in practice.

#he enthalpy of fusion also knon as latent! heat of fusion is the change in enthalpy resulting

from heating a given quantity of a substance to change its state from a solid to a liquid. #he

temperature at hich this occurs is the melting point.

#he RenthalpyR of fusion is a latent heat, because during melting the introduction of heat cannot be

observed as a temperature change, as the temperature remains constant during the process. #he

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latent heat of fusion is the enthalpy change of any amount of substance hen it melts. When the

heat of fusion is referenced to a unit of mass, it is usually called the specific heat of fusion, hile

the molar heat of fusion refers to the enthalpy change per amount of substance in moles.

#he liquid phase has a higher internal energy than the solid phase. #his means energy must be

supplied to a solid in order to melt it and energy is released from a liquid hen it free;es, because

the molecules in the liquid e%perience eaker intermolecular forces and so have a higher potential

energy &a kind of bond-dissociation energy for intermolecular forces'.

When liquid ater is cooled, its temperature falls steadily until it drops ust belo the line of free;ing

point at 2 S6. #he temperature then remains constant at the free;ing point hile the ater

crystalli;es. (nce the ater is completely fro;en, its temperature continues to fall.

VAPORIZATION ENTHALPY OFELECTROLYTE SOLUTIONS

$stimation of the enthalpy of vapori;ation of electrolyte solutions can be simply carried out using

equations based on the chemical thermodynamic models, such as Git;er model or #6G6 model.

COOLING EFFECT OF

EVAPORATIONiquid evaporating from a surface has a cooling effect. "nd different liquids have this effect to different

degrees. For e%ample, rubbing alcohol has more of an evaporative cooling effect than does ater.

 "lcohol is hat is called a volatile liquid, meaning simply that it evaporates comparatively more quickly

than ater. +ut regardless of the liquid, the principle of evaporative cooling is the same. #he idea is that

in its liquid state, the substanceUhether ater or alcoholUhas a certain heat content. 6ritical to this are

to of the three basic phases of matter8 liquid and vapor. &#he solid phase is, of course, the third.'

 $vaporation is the conversion of ater to vapour at a temperature belo boiling point.

Water has a R/apour GressureR at any temperature belo 122S6 at atmospheric pressure. &"t the boiling

point, ater is V(# evaporating, itRs /aporising. $vaporation takes place belo the boiling temperature'.

#he molecules leaving the ater as vapour are moved aay by any movement of air above the ater and

therefore cannot return to the ater. #he $nergy required to evaporate the ater is called Ratent eatR

and takes place by removing the necessary heat from the ater as R!ensible eatR thereby decreasing

the ater temperature.

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&#his principle is also used by the body on a arm day.

#he body gets hot, it seats, the seat evaporates off the skin and the body cools don'.

 "nd, #humbs Honer, as )Rve orked in the (il and =as )ndustry for over K2 years, donRt try to tell me

about $vaporation, /aporisation and, eat and #emperature &hich as you probably donRt kno, are V(#

the same thing'. "lso eat $%change Grinciples and $quipment.

Wh! " #$%&$' (")*+", $, /*#0&# 0*!(+, 1+*/ ,h #$%&$' )h" ,* ,h (")*+)h" "!' 0") 1+*/ ,h &+1"0. Wh", '+$( ,h$ )+*0 $ h",. I! *+'+ 1*+

,h /*#0&# ,* #"( ,h #$%&$' &+1"0 "!' 0") " " (")*+ $, /&, ," h",

!+4 5$,h $,. Th h", ,h", $, ," 5$,h $, 0*/ 1+*/ ,h &+1"0 1+*/ 5h$0h $,

(")*+",'. S$!0 ,h /*#0&# $ ,"$! h", 5$,h $, " $,6 #"($! ,h$ h" "

0**#$! 70, *! ,h &+1"0 #1, 8h$!'.

Human Perspiration "n e%ample of evaporated cooling is that of human perspiration. We have pores in our skin from

hich liquid ater internal to our skin is escaping and converting to ater vapor in the air. "s thishappens, there is a cooling effect on our skin surface. #his is almost alays happening to one

degree or another. When e are e%posed to an environment that is hotter than hat is comfortable

for us, the degree of perspiration or evaporation increases. "nd it follos that the cooling effect

increases. #he more ater molecules that are escaping from the liquid phase from our skin surface

and from our pores, the more cooling effect there is. "gain, it is because the liquid molecules, as

they escape and become vapor, require heat and they take it ith them..

IND INCREASES EVAPORATION

P#"!, '* */,h$! $/$#"+. I! )#"!, ,h )+*0 $ 0"##' ,+"!)$+",$*!.

P#"!, +**, 9'+$!9 5",+ 1+*/ ,h *$# "!' ,+"!)*+, $, &) ,h+*&h ,h ,/

,* ,h #"(. P#"!, #"( h"( ,+&0,&+ 0"##' ,*/",". Th "+

!,$"##4 )*+ ,h", 4*& 0"! ,h$! *1 " 0*/)"+"8# ,* ,h )*+ $! *&+

$!.

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O! *1 ,h /"$! 1&!0,$*! *1 ,h$ )+*0 $! )#"!, $ ,* ,+"!)*+, 5",+!'' 84 )#"!, ,$& $! *,h+ )"+, *1 ,h )#"!, 8$' ,h +**,. B&,

"!*,h+ 1&!0,$*! 1*+ ,h )#"!, $ (")*+",$( 0**#$!. Th$ ) ,h )#"!,

5h$0h /$h, (+4 5## 8 ;)*' ,* '$+0, $!,! &!#$h,1+*/

*(+h",$!. A!' ,h$ $ )"+,#4 "#* 5h4 *! " h*, '"4 $1 5 !,+ " 1*+,'

"+" 5 1# 0*!$'+"8#4 0**#+. P"+, *1 ,h", $ '& ,* ,h h"' 8&, )"+, $

"#* '& ,* (")*+",$( 0**#$! 1+*/ ,h ,+ ,h+*&h ,h$ )+*0 *1 

,+"!)$+",$*!.W$!' $!0+" ,h 70, *1 (")*+",$( 0**#$! "!' ,h$ $ "

1"/$#$"+ 0*!0),. A!4*! 5h*< (+ 8! 5$//$! "!' h" 0*/ *&, *1 

,h 5",+ $!,* " 0"#/ !($+*!/!, (+& *! ,h",< 5$!'4 0"! ",,, ,* $,

1#$! 0*#'+ $! ,h 5$!'. Th$ $ 80"& ,h 5$!' $ $!0+"$! ,h

(")*+",$*! +", *1 ,h #$%&$' 5",+ 1+*/ *&+ $! &+1"0 "!' "00#+",$!

,h "/*&!, ,h",< 8$! 0*!(+,' ,* (")*+.

  i!"-C#i$$F%&'(r

I!0$'!,"##4 ,h$ $ "#* ,h 0"& *1 *-0"##' 5$!' 0h$##. E(! $! 0*#'+0*!'$,$*! 5h! 5<+ *&,$' "!' *&+ $! $ ;)*' ,* ,h #/!,

,h+6 " 0+,"$! "/*&!, *1 )+)$+",$*! h"))!$!. Wh! $,< 5$!'4 ,h+ $

/*+ (")*+",$( 0**#$! ,"$! )#"0 1+*/ ;)*' $! Th$ $ ,h 8"$ 1*+

,h *-0"##' 5$!'-0h$## 1"0,*+.

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  E)AMPLE TO SHO

EVAPORATION CAUSE HEATING

 "ny evaporation system includes a vacuum pump. )t also includes an energy source that evaporatesthe material to be deposited. 4any different energy sources e%ist8

• )n the thermal  method, metal material &in the form of ire, pellets, shot' is fed onto

heated semimetal &ceramic' evaporators knon as 5boats5 due to their shape. " pool of melted

metal forms in the boat cavity and evaporates into a cloud above the source. "lternatively the

source material is placed in a crucible, hich is radiatively heated by an electric filament, or the

source material may be hung from the filament itself &filament evaporation'.

• 4olecular beam epita%y is an advanced form of thermal evaporation.

• )n the electron-beam method, the source is heated by an electron beam ith an energy up to

1K ke/.

• )n flash evaporation, a fine ire of source material is fed continuously onto a hot ceramic

bar, and evaporates on contact.

•   Resistive evaporation is accomplished by passing a large current through a resistive ire or 

foil containing the material to be deposited. #he heating element is often referred to as an

5evaporation source5. Wire type evaporation sources are made from tungsten ire and can beformed into filaments, baskets, heaters or looped shaped point sources. +oat type evaporation

sources are made from tungsten, tantalum, molybdenum or ceramic type materials capable of 

ithstanding high temperatures.

!ome systems mount the substrate on an out-of-plane planetary mechanism. #he mechanism

rotates the substrate simultaneously around to a%es, to reduce shadoing.

 "n important e%ample of an evaporative process is the production of alumini;ed G$# film packaging

film in a roll-to-roll eb system. (ften, the aluminum layer in this material is not thick enough to be

entirely opaque since a thinner layer can be deposited more cheaply than a thick one. #he main

purpose of the aluminum is to isolate the product from the e%ternal environment by creating a barrier 

to the passage of light,o%ygen, or ater vapor.$vaporation is commonly used in microfabrication to

deposit metal films$vaporated materials deposit nonuniformly if the substrate has a rough surface

&as integrated circuits often do'. +ecause the evaporated material attacks the substrate mostly from

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a single direction, protruding features block the evaporated material from some areas. #his

phenomenon is called 5shadoing5 or 5step coverage.5

When evaporation is performed in pure vacuum or close to atmospheric pressure, the resulting

deposition is generally non-uniform and tends not to be a continuous or smooth film. ather, the

deposition ill appear fu;;y .

SEVEN E)AMPLES TO

SHO EVAPORATION CAUSE

COOLING

1. During hot summers,the water is usually kept in the earthern potto keep it cool.Water is cooled in the pot since the surface of the pot

contains large pores and water seeps via these pores to outside of

 pot. This water evaporates and takes the latent heat for vaporisation

hence retaining the water inside pot to be cooled.

 2. Especially in villages,people often sprinkle water on the ground

in front of their homes during hot summers.

3. Water vaporisation from leaves of trees also cools the

surroundings.

4. A desert cooler cools better on a hot and dry day.

5. It is a common observation that we are able to sip hot tea(or milk)

faster from a saucer than from a cup.

6. Wearing cotton clothes in summer days to keep the body cool and

comfortable.

7. Put a little of spirit on your hand and wave around, the spirit

evaporates rapidly and our hands feels cooler.

 "n evaporative cooler  &also swamp cooler , desert cooler  and wet air cooler ' is a device that

cools air through the evaporation of ater. $vaporative cooling differs from typical air

conditioning systems hich use vapor-compression or absorption refrigeration cycles. $vaporative

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cooling orks by employing aterRs large enthalpy of vapori;ation. #he temperature of dry air can be

dropped significantly through the phase transition of liquid ater to ater vapor &evaporation', hich

can cool air using much less energy than refrigeration. )n e%tremely dry climates, evaporative

cooling of air has the added benefit of conditioning the air ith more moisture for the comfort of

building occupants.

#he cooling potential for evaporative cooling is dependent on the et bulb depression, the difference

beteen dry-bulb temperature andet-bulb temperature. )n arid climates, evaporative cooling canreduce energy consumption and total equipment for conditioning as an alternative to compressor-

based cooling. )n climates not considered arid, indirect evaporative cooling can still take advantage

of the evaporative cooling process ithout increasing humidity. Gassive evaporative cooling

strategies offer the same benefits of mechanical evaporative cooling systems ithout the comple%ity

of equipment and ductork.

ABSTRACT :-  When e get hot, e seat. #he physiological role of seat is to cool us don. When the

ater evaporates, it removes energy from our bodies. #his sort of evaporative cooling  can also beused to cool homes, using hat are referred to as swamp coolers. $vaporative cooling is also a

potential source of energy aste in the kitchen because it increases the time it takes to heat ater.

)n this chemistry science fair proect, you ill study ho a variety of things cool don, hether for 

better or orse, using the process of evaporation.

"vaporation is the process by hich molecules in a liquid escape into the gas phase. )n any liquid,

such as a glass of ater at room temperature, the molecules in the liquid are moving. #hey bump

into each other as they meander about the liquid. #he speed ith hich they move depends on the

temperatureUin hotter liquids, the molecules move faster. #he average speed depends on

temperature, but around this average speed, there ill be some molecules moving faster &more

energetically', and some moving sloer. When the more-energetic molecules are near the liquidRs

surface, they can escape into the gas above. "s more and more of the most energetic molecules

evaporate into the gas, the average energy of the molecules left behind decreases, so the liquid

cools.

#he rate of cooling caused by evaporation depends on the rate at hich molecules can escape from

the liquid. Xou might have noticed that hen you pour rubbing alcohol on your skin, it cools your skin

more than hen you pour ater on it. #his reflects the greater volatility# or tendency to evaporate,

of the rubbing alcohol.

#he $%perimental Grocedure for this science fair proect has three sections. #hey might seemunconnected at first, but each is related by the underlying concept of evaporative cooling$ )n the

first section of the $%perimental Grocedure, you ill compare evaporative cooling caused by ater,

rubbing alcohol, and cooking oil. #he cooling effect studied in this part of the procedure is the basis

for swamp coolers$ )n these cooling devices, outside air is blon over a et surface and then into

the home. Xou are familiar ith the principle if you have ever had et clothes on ith a bree;e

bloingUthe evaporation of ater cools you off, ust as it cools the et surface in the samp cooler.

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#hermal energy in the hot air is 5e%tracted5 and used to convert some of the liquid ater into ater 

vapor. +ecause energy is used to evaporate ater, the air is cooled after passing over the et

surface. #he cool air is then circulated around the interior of the building.

)n the second section of the procedure, you ill look at the temperature change that occurs hen

ater &seat' evaporates off of skin. !eating is a physiological response that uses evaporative

cooling as a mechanism to remove e%cess heat.

)n the third section, you ill look at evaporative cooling in the kitchen. When heat is applied to ater 

to make it boil, some of the energy can be lost to evaporative cooling. Xou ill investigate ho

evaporative cooling affects boiling time by comparing ho long it takes to boil a pot of ater both

ith and ithout a lid.

E)PERIMENT :-

O8=0,$( :-TO DETERMINE HOW EVAPORATIONEE!T" ON HEATING AND !OOLING

M%'eri%$* %!" E+ui,e!'

re+uire" :- 

%easuring cup

  &ater 

  'ubbing alcohol

 

Coo(ing oil# such as olive oil

 

Plastic plates# disposable )!

  Paper towels *+!

  Clear tape

  ,allpoint pen

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  Infrared thermometer 

 

Stopwatch

  Small fan if you do not have a small fan# you will need an e.tra plate$

 

Pots to boil water# identical# +-/t$ size or larger# with lids +! you can use one potrepeatedly if you do not have identical pots$

  Stovetop

  0 helper 

  1ab noteboo(

 

2raph paper 

E.,erie!'%$Pr(&e"ure :-

E(")*+",$( C**#$! $!

B&$#'$! :-*$ Fill a measuring cup with tap water and allow it to come to room temperature$

a$ The rubbing alcohol and the oil should also be at room temperature$

b$ This step is 3ust to ensure that the li/uids are at the same temperature at the start

of the e.periment$

+$ Place four disposable plastic plates# with the up sides down# on a wor( surface$

a$ 4se a waterproof surface such as tile or laminate! since you will be using alcohol

that could damage wood finish$

5$ Fold each paper towel in half twice# so that each has four layers$

)$ Place a folded paper towel on top of each plate$

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a$ The plates (eep the towels from being in contact with the wor( surface# which

would affect their temperature$ 6ou could also use StyrofoamT% or other insulating

material$

7$ Tape the edges of the paper towels to the plates$

8$ 1abel the paper towels *9)$

a$ In the ne.t step# the paper towels will be treated as follows:

  *: no li/uid

 

+: water 

  5: rubbing alcohol

  ): oil

$ Start the stopwatch$

;$ Ta(e the temperature of the paper towels with the infrared thermometer$

a$ Ta(e three readings of each paper towel$

b$ <eep the direction and distance between the thermometer and each plate the

same$

c$ 'ecord the temperatures and times in a data table in your lab noteboo($

=$ Pour water on paper towel >+# 3ust enough to wet it$

*?$ Pour rubbing alcohol on paper towel >5# 3ust enough to wet it$

**$ Pour oil on paper towel >)# 3ust enough to wet it$

*+$ Ta(e the temperature of each paper towel# and record the temperature and time in your lab

noteboo($

*5$ 'epeat the temperature readings three more times# at +-minute intervals$

*)$ &hich paper towel has the lowest temperature@ &hat was the largest temperature

difference between two paper towels that you noted@ 'ecord all observations in your lab

noteboo($

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*7$ 'epeat steps *-*) two more times# with fresh paper towels# but you can rinse and reuse

the plates$ 0verage the results in your final report$

*8$ 'epeat steps *-*7 three more times# only for these trials# with the fan gently blowing over

the paper towels$ If you do not have a fan# use a paper plate as a fan$ 6our helper can fan

as you ta(e and record the temperature at +-minute intervals$ Aid the fan change the

results@ &hy@

E(")*+",$( C**#$! *! S$! :-In this section# you will loo( at the cooling effect of evaporation on human s(in$

*$ %ar( a small spot on your arm with a ballpoint pen$

+$ %easure the temperature of the s(in on your forearm near the pen mar($

a$ 0s in the section before# ta(e two more readings and average them$

5$ Pour some room-temperature water on your arm$

)$ Ta(e the temperature of your s(in near the mar($ 'ecord all data in your lab noteboo($

7$ Ta(e a temperature reading every minute until your arm dries$

8$ 'epeat steps *-7 two more times$

$ Bow repeat steps *-8 of this section three times# this time using the fan or helper with thepaper plate to blow air on your arm$ 0verage all the results$

;$ 2raph your results$

=$ &hat temperature change did you see@

*?$ 'epeat steps *-= of this section using rubbing alcohol$ &hat is the difference in the

temperatures between water and alcohol@

E(")*+",$( C**#$! Wh!B*$#$! W",+ :-

 6ou have loo(ed at two beneficial aspects of evaporative coolingone used to cool buildings and

one used to cool people$ In this section# you will loo( at a situation where evaporative cooling is a

source of energy waste and thus# something to avoid$

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*$ 0dd + /t$ ; cups! of tap water to each pot$

+$ Chec( the starting temperature of the water with the infrared thermometer$ 'ecord the

time and temperatures in your lab noteboo($

5$ Start two burners on your stovetop$ They should be set to the same setting$

)$ Cover one of the pots with a lid# but not the other$

7$ Put the pots on the burners$

8$ 4se the infrared thermometer to record the temperature of the water every 5 minutes$

o %easure the temperature of the open pot by pointing the thermometer at the

surface of the water$

o %easure the temperature of the covered pot by briefly removing the lid and

pointing the thermometer at the surface of the water$

$ Aetermine how long it ta(es for the water in each pot to come to a boil$

;$ Stop ta(ing the temperature of a pot when it is at a full boil$ 4se your 3udgment as to when

this point is reached$

=$ 'epeat two more times and average your results$

*?$ 2raph your results$ Put DCoveredD and D4ncoveredD on the .-a.is# and DTime to boilD on

the y-a.is$ &hat was the time-to-boil difference between the two pots# in minutes and in

percent change

VARIATIONS :-

 

Try other li/uids for the first section# such as

sugar or salt solutions# nail polish remover# etc$

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If you have access to a sensitive scale# weigh the

paper towel with the alcohol during the course of the procedure$ Find a relationship between weightchange and temperature$ For e.ample# Don

average# * gram g! of alcohol was evaporatedevery minute to (eep the paper towel 5 degreescooler than room temperature$D

  Aemonstrate how a swamp cooler wor(s in a

model house made out of cardboard$ 1oo( upsome design ideas online$ 'emember# the air coming in from the fan needs an open window or 

door to escape out of$ This is a consideration for real houses with swamp coolers$

 

Ao some research on the energy used by your 

stove and calculate how much energy you used toboil the water on your stovetop with and withoutthe lid$ 6ou might loo( at the gas meter to

estimate how much gas is used$ %a(e somerough guesses to come up with an estimate of how much energy could be saved nationally if everyone used a lid on a pot of water set to boil$

 

Aevise a method for reliably measuring small

changes in temperature due to evaporation of low-volatility li/uids# such as oil$

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BIBLIOGRAPHY :-

OR !OMPLETING THI" PRO#E!T $O%R

BA!&GRO%ND RE"EAR!H' WE TA&E HELP O THE

OLLOWING ARE :-

  REEREN!E" :-()ALL IN ONE )

  *)PRADEEP)

  INTERNET WEB"ITE" :-()WWW)"LIDE "HARE)!OM

  *) WWW)"!IEN!E B%DDIE")!OM  +) WWW)"EMINAR"

ONLY)!OM

  TEA!HER"

  RIEND"

  N)!)E)R)T BOO&"

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