report refrigeration systems

8/12/2019 Report Refrigeration Systems

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Port-Siad University

Faculty of Engineering

Mechanical Power Engineering Dept.

Postgraduate Level

Report !out

REFRIGERATION SYSTEMS

Prepared By

Eng/ Ahmed Mohamed Salman Salem

Presented To

Dr / Nasser Shelil

"#$% & "#$'


2/22

Table of Contents

CH (! INTRO"#CTION AN" RE$ERSE" CARNOT CYC%E

$. (ntroduction

". Reversed )arnot )ycle

CH (&! $APOR COMPRESSION REFRIGERATION TECHNO%OGIES

$. *he (deal +apor-)o,pression Refrigeration )ycle

". *he ctual +apor-)o,pression Refrigeration )ycle

%. Effect of perating *e,peratures on the Perfor,ance of Refrigeration Unit

%.$ Effect of Evaporation *e,perature

%." Effect of )ondensing *e,perature

CH ('! ABSORPTION REFRIGERATION TECHNO%OGIES

$. (ntroduction

". Principle of operation

%. or/ing fluid for a!sorption refrigeration syste,s

'. Effects of 0enerator *e,perature 1*02 and Environ,ent *e,perature 1*E2 on )oefficient of

Perfor,ance 1)P2 for !sorption Refrigeration )ycle

3. +arious designs of a!sorption refrigeration cycles

3.$. Single-effect a!sorption syste,

3.". !sorption heat transfor,er

3.%. Multi-effect a!sorption refrigeration cycle

3.'. !sorption refrigeration cycle with 04

3.3. !sorption refrigeration cycle with an a!sor!er-heat-recovery

3.5. 6alf-effect a!sorption refrigeration cycle

3.7. )o,!ined vapor a!sorption-co,pression cycle

3.8. Dual-cycle a!sorption refrigeration

REFERENCES


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)6 1$2

(9*RDU)*(9 9D RE+ERSED )R9* ):)LE

Introd)*t+on

Refrigeration can !e defined as the !ranch of engineering science that deals with the study of a!sor!ingheat fro, a certain space to reduce is te,perature and ,aintain it constant at low value. *o acco,plish this;

heat ,ust re,oved fro, the space or a !ody !eing refrigerated and transferred to another space or another!ody. *he cooled space ,ay !e li6is the ,agnitude of the heat re?ected to the war, space at

te,perature *6; and net;in is the net wor/ input to the refr+,erator.

nother device that transfers heat fro, a low-te,perature ,ediu, to a high-te,perature one is the

-eat p).p. Refrigerators and heat pu,ps are essentially the sa,e devices@ they differ in their o!?ectives

only. *he o!?ective of a refrigerator is to ,aintain the refrigerated space at a low te,perature !y re,ovingheat fro, it. Discharging this heat to a higher-te,perature ,ediu, is ,erely a necessary part of theoperation; not the purpose. *he o!?ective of a heat pu,p; however; is to ,aintain a heated space at a high

te,perature. *his is acco,plished !y a!sor!ing heat fro, a low-te,perature source; such as well water or

cold outside air in winter; and supplying this heat to a war,er ,ediu, such as a house 1Fig. $$&$!2.

*he perfor,ance of refrigerators and heat pu,ps is eApressed in ter,s of the *oeff+*+ent of perfor.an*e

1)P2; defined asB


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*he cooling capacity of a refrigeration syste,Cthat is; the rate of heat re,oval fro, the refrigerated space is

often eApressed in ter,s of tons of refr+,erat+on *he capacity of a refrigeration syste, that can free=e $ ton

1"### l!,2 of li


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)6 1"2

+PR )MPRESS(9 REFR(0ER*(9 S:S*EM

T-e Ideal $apor0Co.press+on Refr+,erat+on Cy*leMany of the i,practicalities associated with the reversed )arnot cycle can !e eli,inated !y vapori=ing

the refrigerant co,pletely !efore it is co,pressed and !y replacing the tur!ine with a throttling device; such

as an eApansion valve or capillary tu!e. *he cycle that results is called the +deal/apor0*o.press+onrefr+,erat+on *y*le1 and it is shown sche,atically and on a T-s diagra, in Fig. $$&%. *he vapor-co,pressionrefrigeration cycle is the ,ost widely used cycle for refrigerators; air-conditioning syste,s; and heat pu,ps.

(t consists of four processesB

$-" (sentropic co,pression in a co,pressor"-% )onstant-pressure heat re?ection in a condenser

%-' *hrottling in an eApansion device

'-$ )onstant-pressure heat a!sorption in an evaporator

(n an ideal vapor-co,pression refrigeration cycle; the refrigerant enters the co,pressor at state $ assaturated vapor and is co,pressed isentropically to the condenser pressure. *he te,perature of the refrigerant

increases during

this isentropic co,pression process to well a!ove the te,perature of the surrounding ,ediu,. *he refrigerantthen enters the condenser as superheated vapor at state " and leaves as saturated li


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is loered.

nother diagra, fre


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&T-e A*t)al $apor0Co.press+on Refr+,erat+on Cy*len actual vapor-co,pression refrigeration cycle differs fro, the ideal one in several ways; owing

,ostly to the irreversi!ilities that occur in various co,ponents. *wo co,,on sources of irreversi!ilities are

fluid friction 1causes pressure drops2 and heat transfer to or fro, the surroundings. *he T-s diagra, of an

actual vapor-co,pression refrigeration cycle is shown in Fig. $$&7.

(n the ideal cycle; the refrigerant leaves the evaporator and enters the co,pressor assaturated vapor. (npractice; however; it ,ay not !e possi!le to control the state of the refrigerant so precisely. (nstead; it is easier

to design the syste, so that the refrigerant is slightly superheated at the co,pressor inlet. *his slightoverdesign ensures that the refrigerant is co,pletely vapori=ed when it enters the co,pressor. lso; the lineconnecting

the evaporator to the co,pressor is usually very long@ thus the pressure drop caused !y fluid friction and heat

transfer fro, the surroundings to the refrigerant can !e very significant. *he result of superheating; heat gain

in the connecting line; and pressure drops in the evaporator and the connecting line is an increase in thespecific volu,e; thus an increase in the power input re


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'Effe*t of Operat+n, Te.perat)res on t-e Perfor.an*e of Refr+,erat+on #n+t*he perfor,ance of the vapor co,pression refrigeration syste, varies with !oth evaporating and

condensing te,perature. So; any change of any of the, will affect the perfor,ance of the unit. *he

para,eters; those ,ay !e affected !y any change of the operating conditions areB refrigeration capacity;

power re


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Effect of Evaporation Temperature on the performance of refrigeration unit

3.2 Effect of Condensing Temperature

Figure shown represents the 1P-i2 diagra, for the si,ple refrigeration syste, when the condensing unitis changing. *he effect of increasing the su,,ari=ed in the followingB

$- *he refrigeration effect decreases.

"- *he ,ass flow rate per unit *.R increases.

%- *he R.) of the unit decreases.

'- *he specific power re


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)6 1%2

GSRP*(9 REFR(0ER*(9 *E)69L0(ES

Introd)*t+on

Most of industrial process uses a lot of ther,al energy !y !urning fossil fuel to produce stea, or heatfor the purpose. fter the processes; heat is re?ected to the surrounding as waste. *his waste heat can !e

converted to useful refrigeration !y using a heat operated refrigeration syste,; such as an a!sorptionrefrigeration cycle. Electricity purchased fro, utility co,panies for conventional vapor co,pression

refrigerators can !e reduced. *he use of heat operated refrigeration syste,s help reduce pro!le,s related to

glo!al environ,ental; such as the so called greenhouse effect fro, )" e,ission fro, the co,!ustion of

fossil fuels in utility power plants.

nother difference !etween a!sorption syste,s and conventional vapor co,pression syste,s is the

wor/ing fluid used. Most vapor co,pression syste,s co,,only use chlorofluorocar!on refrigerants 1)F)s2;

!ecause of their ther,o-physical properties. (t is through the restricted use of )F)s; due to depletion of the

o=one layer that will ,a/e a!sorption syste,s ,ore pro,inent. 6owever; although a!sorption syste,s see,

to provide ,any advantages; vapor co,pression syste,s still do,inate all ,ar/et sectors. (n order topro,ote the use of a!sorption syste,s; further develop,ent is re


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henever the solution cannot continue with the a!sorption process !ecause of saturation of the

refrigerant; the refrigerant ,ust !e separated out fro, the diluted solution. 6eat is nor,ally the /ey for thisseparation process. (t is applied to the right vessel in order to dry the refrigerant fro, the solution as shown

in Fig. $1!2.

*he refrigerant vapor will !e condensed !y transferring heat to the surroundings. ith these processes;

the refrigeration effect can !e produced !y using heat energy.

6owever; the cooling effect cannot !e produced continuously as the process cannot !e done

si,ultaneously. *herefore; an a!sorption refrigeration cycle is a co,!ination of these two processes asshown in Fig. ". s the separation process occurs at a higher pressure than the a!sorption process; a

circulation pu,p is re


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4. Effects of Generator Temperature (TG!and Environment Temperature (TE!on Coefficient

of Performance (COP!for Absorption Refrigeration Cyce!

4 $ar+o)s des+,ns of absorpt+on refr+,erat+on *y*les

".1. #inge$effect absorption system

single-effect a!sorption refrigeration syste, is the si,plest and ,ost co,,only used design. *here

are two design configurations depending on the wor/ing fluids used. Fig. % shows a single-effect syste,using non-volatility a!sor!ent such as LiGrwater.


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6igh te,perature heat supplied to the generator is used to evaporate refrigerant out fro, the solution1re?ected out to the surroundings at the condenser2 and is used to heat the solution fro, the a!sor!er

te,perature 1re?ected out to the surroundings at the a!sor!er2. *hus; an irreversi!ility is caused as high

te,perature heat at the generator is wasted out at the a!sor!er and the condenser. (n order to reduce thisirreversi!ility; a solution heat eAchange is introduced as show in Fig. %. *he heat eAchanger allows the

solution fro, the a!sor!er to !e preheated !efore entering the generator !y using the heat fro, the hot

solution leaving the generator. *herefore; the )P is i,proved as the heat input at the generator is reduced.

Moreover; the si=e of the a!sor!er can !e reduced as less heat is re?ected. EAperi,ental studies shows that)P can !e increased up to 5#Q when a solution heat eAchanger is used %7.

hen volatility a!sor!ent such as water96% is used; the syste, re


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Fig. ' shows a sche,atic diagra, of an a!sorption heat transfor,er. *his cycle has si,ilar

co,ponents as a single-effect a!sorption cycle. *he difference is that an eApansion device installed !etweenthe condenser and the evaporator is su!stituted !y a pu,p. aste heat at a relatively low te,perature is

supplied to the generator

for refrigerant separation in the usual ,anner. Li


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the first-effect generator is $)Psingle. For any single-effect a!sorption syste,; it ,ay !e assu,ed that the

heat re?ected fro, the condenser is approAi,ately e


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dou!le-effect a!sorption syste,. Several types of ,ulti-effect a!sorption cycle has !een analy=ed such as the

tripleeffect a!sorption cycle 1Fig. 72 58 and the


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".". Absorption refrigeration cyce 'it% an absorber$%eat$recovery

(t is already ,entioned earlier that the use of a solution heat eAchanger i,proves the syste, )P.

Rich-refrigerant solution fro, the a!sor!er can !e preheated !efore entering the generator !y transferring

heat fro, hot solution co,ing fro, the generator. Gy introducing an a!sor!er-heat-recovery; te,perature ofthe rich-refrigerant solution can !e further increased.

Si,ilar to the 04 syste,; the a!sor!er is divided into two sections. 6eat is re?ected out at a differentte,perature. *he lower te,perature section re?ects heat out to the surroundings as usual. 6owever; the

higher te,perature section is used

to preheat rich-refrigerant solution as shown in Fig. N. *herefore; the heat input to the generator is reduced

causing the )P to increase. *his syste, was studied theoretically !y using various wor/ing fluids@water96% and Li9%96% 7N;8#. *he cycle with an a!sor!er-heat-recovery was found to have $#Q

i,prove,ent in )P. 6owever; the ,achine !ased on this a!sor!er design has not yet !een !uilt.

".). *af$effect absorption refrigeration cyce

(t ,ust !e noted that; any a!sorption refrigeration syste, can !e operated only when the solution in thea!sor!er is richer in refrigerant than that in the generator. hen the te,perature increases or the pressure

reduces; the fraction of refrigerant contained in the solution is reduced; and vice versa. hen the generatorte,perature is dropped; the solution circulation rate will !e increased causing the )P to drop. (f it is toolow; the syste, can !e no longer operated.

*he half-effect a!sorption syste, was introduced for an application with a relatively low-te,perature

heat source 8$. Fig. $# shows a sche,atic diagra, of a half-effect a!sorption refrigeration cycle. *he

syste, configuration is eAactly the sa,e as the dou!le-effect a!sorption syste, using water96% 1as shownin Fig. 52 eAcept the heat flow directions are different. Referring to Fig. $#; high te,perature heat fro, an

eAternal source transfers to !oth generators. Goth a!sor!ers re?ect heat out to the surroundings. !sor!er ((

and generator ( are operated at an inter,ediate pressure level. *herefore; the circulation rate !etweengenerator ( and a!sor!er ( and !etween generator (( and a!sor!er (( can !e ,aintained at accepta!le levels. (t


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,ust !e noted that )P of the half-effect a!sorption syste, is relatively low as it re?ects ,ore heat than a

single-effect a!sorption cycle around 3#Q 8". 6owever; it can !e operated with the relatively lowte,perature heat source.

".+. Combined vapor absorption$compression cyce

*his syste, is usually /nown as an a!sorption-co,pression syste,. sche,atic diagra, of a typicala!sorptionco,pression cycle is shown in Fig. $$1a2. (t can !e seen that; a condenser and an evaporator of a

conventional vapor-co,pression syste, are replaced with a resor!er 1vapor a!sor!er2 and a desor!er 1vapor

generator2. For given surrounding te,perature and refrigerating te,perature; the pressure differential acrossthe co,pressor is ,uch lower than a conventional vapor-co,pression syste,.

*hus; the )P is eApected to !e !etter than a conventional vapor-co,pression syste,. lten/irch did

the first investigation in $N3# and proposed a potential for energy-saving 8". *he cycle can !e configured


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as a heat pu,p cycle. Machielsen 8% developed a heat pu,p cycle as shown in Fig. $$1!2. n interesting

configuration is a dou!le-effect vapor a!sorptionco,pression cycle

as shown in Fig. $". *he re?ected first-stage a!sor!er heat is supplied to the generator of the second-stage. *he transfer of heat is done internally which overco,es the large te,perature difference at the

,oderate pressure ratio. *his concept has !een shown successfully in several studies; 8%&83.

nother configuration of the vapor a!sorptionco,pression cycle; proposed !y )acciola et al. 85 is

shown sche,atically in Fig. $% and e,ploys two co,!inations of wor/ing fluids; water96% andT6water. *his is a co,pro,ise of the water96% cycle and T6water cycle. *he highest syste,

pressure is reduced and the rectifier of water96% syste, is a!stained. *his cycle can !e operated with an

a,!ient te,perature lower than #) without free=ing or crystalli=ation pro!le,s.

*he first eAperi,ental results of an a!sorptionco,pression cycle with direct


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".,. -ua$cyce absorption refrigeration

*he concept of a dual-cycle a!sorption syste, is si,ilar to a parallel-dou!le-effect a!sorption syste,.

6owever; this syste, consists of two co,pletely separated cycles using different /inds of wor/ing fluid.

6anna et al. 88 invented a dual-cycle a!sorption refrigeration and heat pu,p as shown in Fig. $3. *hissyste, consists of two single-effect a!sorption cycles using water96% and LiGrwater. *he 96% syste, is

driven !y heat o!tained fro, an eAternal heat source. *he heat re?ect fro, its a!sor!er and condenser is used

as a driving heat for the LiGrwater syste,. *he LiGrwater syste, re?ects heat out to the surrounding at thecondenser and the a!sor!er as usual. *he cooling effect can !e o!tained fro, !oth evaporators.


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REFERE9)ES

$- *her,odyna,ics n Engineering pproach; Fifth edition; :unus .)engel.

"- Fro, lectureKs notes fro, the we!.

%- review of a!sorption refrigeration *echnologies; Pongsid Sri/hirin ; Satha

phornratana; Supachart )hungpai!ulpatana; Renewa!le and Sustaina!le Energy

Reviews 3 1"##$2 %'%&%7".

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