exp 1 - refrigeration unit

8/13/2019 Exp 1 - Refrigeration Unit

1/33

1. Abstract

This experiment was conducted using the refrigeration apparatus system with

typical operating conditions in evaluating the performance of a refrigeration cycle.

Refrigerator works by the transfer of heat from a lower temperature region to a higher

temperature one. The working fluid used in the refrigeration cycle is called refrigerant.

This experiment was done in four parts in which the first part was to determine the

power input, heat output, and coefficient of performance (CO!. The second part was

to determine the production of heat pump over a range of source and delivery

temperature and the third part was to determine the production of vapour compression

cycle on p"h diagram and energy balance study. The fourth part was to determine the

compression ratio and volumetric efficiency. #or the first part, the results obtained

were, power input, 197 W; heat output, 45.576 kJ/minand CO is 0.47.#or the

second part, we plotted three($! graphs of CO vs. delivered water temperature, %&

vs. delivered water temperature, and compressor vs. delivered water temperature and

we have identified the relation of temperature with the performance of the cycle and

the heat released. 'n the third part, we plotted the p"h diagram for the cycle and also

the energy balance for condenser and compressor where from the graph plotted we

assumed that the cycle is not an ideal cycle. #or the last part, we obtained 0.699for

volumetric efficiency and 0.38for pressure ratio.

1


2/33

2. Introduction

The primary purpose of a refrigeration system is to remove heat energy at a low

temperature from a conditioned spacebody and transfer this heat energy into another

medium at a higher temperature. The e)uipment is compact, bench mounted and

instrumented. The heat pump consists of a hermetic compressor, a water cooled

condenser, a thermostatically controlled expansion valve and an air heated

evaporator. The arrangement of the components are in a manner similar to that used

for many domestic air"water heat pumps where they are visible from the front of the

unit.

*uring the operation, slightly superheated refrigerant (R+$a! vapour enters the

compressor from the evaporator and its pressure is increased. Thus, the

temperature rises and the hot vapour then enters the water cooled condenser. &eat is

given up to the cooling water and the refrigerant condenses to a li)uid before passing

to the expansion valve. -pon passing through the expansion valve the pressure of the

li)uid refrigerant is reduced. This causes the saturation temperature to fall to below

that of the atmosphere. Thus, as it flows through the evaporator, there is a

temperature difference between the refrigerant and the air being drawn across the

coils. The resulting heat transfer causes the refrigerant to boil, and upon leaving the

evaporator it has become slightly superheated vapour, ready to return to thecompressor.

2


3/33

The temperature at which heat is delivered in the condenser is controlled by the

water flow rate and its inlet temperature. The evaporating temperature is largely

determined by the ambient conditions. &owever, this can be limited, either by

restricting the air intake to the evaporator, or by directing warmed air towards the

intake. 'nstrumentations are all provided for the measurement of flow"rates of both therefrigerant and cooling water, power input to the compressor, and

all relevant temperatures.

3. !"or#

The vapor"compression refrigeration cycle is the ideal model for refrigeration

systems where the refrigerant is vaporied completely before it is compressed and it

is the most widely used cycle for refrigerators, air"conditioning systems, and heat

pumps. This cycle consists of four processes which are/ (Cengel, 0oles1 2334!

a. +"2 (compressor! 'sentropic compression

b. +"$ (condenser! Constant pressure heat re5ection

c. $" (expansion valve! throttling, isenthalpic

d. "+ (evaporator! constant pressure and temperature heat addition

3


4/33


5/33

#igure +/T"s diagram for ideal vapor"compression refrigeration cycle.

$om%r"ssor& The low"pressure saturated vapor refrigerant from the evaporator is

drawn into the compressor, where its pressure is increased and delivered to the

condenser. The compressor is of the diaphragm type and is directly coupled to an

electric motor.

$ond"ns"r& The condenser is a heat exchanger where the high"pressure vapor from

the compressor condenses as it transfers heat to the cooling water, which becomes

warmer.

!rott'"&7s the high"pressure high temperature li)uid refrigerant passes the throttling

valve seating, its pressure and temperature drop to that of the evaporator. The drop in

temperature is accompanied by the formation of 8flash vapor9, so a mixture of low"

pressure and temperature li)uid and vapor enter the evaporator.

()a%orator& The low"pressure li)uid and vapor refrigerant mixture enters the

evaporator and separate1 the li)uid stays in a 8pool9 for re"evaporation, while vapor

mixes with the other vapor passing to the compressor absorbing heat from the water.

5


6/33

*"asur"m"nt o+ %"r+ormanc"

The usual measure of performance of a refrigerator or heat pump is the Coefficient

of PerformanceCO which for a refrigerator CORis defined as/

E

R

heat absorbed at the lower temperatureCOP

compressor net work

Q

W= =

(+a!

#or a heat pump CO&/

C

H

heat rejected at the higher temperatureCOP

compressor net work

Q

W= =

(+b!

where :, C, R, & stand for :vaporator, Compressor, Refrigeration, and &eat pump

respectively.

(,%"rim"nt 1&

6apor compression cycle;s principle of operation is actually )uite simple. 7 working

fluid is boiled in an evaporator at a pressure and hence temperature, T


7/33

condensed the working fluid li)uid is then expanded (via an expansion valve! back into

the evaporator where it can again provide cooling at a low temperature.

To calculate the power input, heat output and coefficient of performance1 we used

the formulas given which are1

Coefficient of Performance;

Heat output per time;

-o"r in%ut;

(,%"rim"nt 2&

The heat delivered by a heat pump is theoretically the sum of the heat extracted

from the heat source and the energy needed to drive the cycle. The steady"state

performance of an electric compression heat pump at a given set of temperature

conditions is referred to as the coefficient of performance (CO!. 't is defined as the

ratio of heat delivered by the heat pump and the electricity supplied to the compressor.

The CO or :R of a heat pump is closely related to the temperature lift, i.e. the

difference between the temperature of the heat source and the output temperature of

the heat pump. The CO of an ideal heat pump is determined solely by the

condensation temperature and the temperature lift (condensation " evaporation

temperature!.

7


8/33

#igure below shows the CO for an ideal heat pump as a function of temperature

lift, where the temperature of the heat source is 3>C. 7lso shown is the range of actual

COs for various types and sies of real heat pumps at different temperature lifts.

The ratio of the actual CO of a heat pump and the ideal CO is defined as the

Carnot"efficiency. The Carnot"efficiency varies from 3.$3 to 3.? for small electric heat

pumps and 3.? to 3.4 for large, very efficient electric heat pump systems.

(,%"rim"nt 3&

ressure"enthalpy diagram defines the thermodynamic properties for the refrigerant

in use and the performance of e)uipment.

8


9/33

The region on the left is sub"cooled li)uid

The region inside the ;;dome@ is a li)uid"vapor mixture.

'f the li)uid is at the boiling point, but hasn;t begun to boil, it is defined as

saturated li)uid. 7dding any heat to this li)uid will vaporie some of it. #urther

addition of heat to the li)uid"vapor mixture eventually evaporates all of the

li)uid. 7t that precise point (A!, the vapor is fully saturated. 7dding any more

heat to the vapor will cause superheated vapor state.

Be use the data obtained from the experiment to calculate the enthalpy obtained

from steam table 7"+2. (may use interpolation!.

Carnot cycle is the most efficient heat engine cycle which consist of two isothermal

processes and two adiabatic processes. This cycle can be considered as the most

efficient heat engine cycle allowed by physical laws. Bhen the second law of

thermodynamics states that not all the supplied heat in a heat engine can be used to

do work, the Carnot efficiency sets the limiting value on the fraction of the heat which

can be so used.

'n order to approach the Carnot efficiency, the processes involved in the heat

engine cycle must be reversible andinvolve no change in entropy. This means that the

9


10/33

Carnot cycle is an idealiation, since no real engine processes are reversible and all

real physical processes involve some increase in entropy.

(,%"rim"nt 4&

'n determining the compression ratio, we use

and the formulae below to calculate the volumetric efficiency.

4. b"cti)"s

(,%"rim"nt 1&

To determine the power input, heat output and coefficient of performance of a vapour

compress on heat pump system.

10


11/33

(,%"rim"nt 2&

To produce the performance of heat pump over a range of source and temperature.

(,%"rim"nt 3&

To plot the vapour compression cycle on p"h diagram and energy balance study1

To perform energy balances for the condenser and the compressor.

(,%"rim"nt 4&

To determine the compression ratio and volumetric efficiency.

5. A%%aratus and *at"ria's

11


12/33

#igure +/ O


13/33

Tap water.

6. *"t!odo'o#

"n"ra' tartu% -roc"dur"s

+. The unit and all instruments were checked so that they are in proper condition.

2. 0oth the water source and drain were checked so that they are connected and

the water supply was opened and the cooling water flow rate was set at 3G.

$. The drain hose at the condensate collected was check so that they are

connected.

. The power supply was connected and the main power followed by main switch

at the control panel were switched on.

?. The refrigerant compressor was switched on. 7s soon as the temperature and

pressure are constant, the unit is ready for experiment.

(,%"rim"nt 1& "t"rmination o+ -o"r In%ut: "at ut%ut and $o"++ici"nt o+

-"r+ormanc".

+. The general start"up procedures was performed.

2. The cooling water flow rate was ad5usted to 3G.

$. The system was allowed to run for +? minutes.

13


14/33

. 7ll necessary readings were recorded into the experimental data sheet.

(,%"rim"nt 2& -roduction o+ "at -um% -"r+ormanc" $ur)"s )"r a an" o+

ourc"s and "'i)"r# "m%"ratur".

+. The general start"up procedures was performed.

2. The cooling water flow rate was ad5usted to E3G.

$. The system was allowed to run for +? minutes.

. 7ll necessary readings were recorded into the experimental data sheet.

?. The experiment was repeated with reducing water flow rate to D3G and 3G so

that the cooling water outlet temperature increases by about $3oC.

D. The experiment was repeated at different ambient temperature.

4. The performance curves for heat pump (coefficient of performance, heat

delivered, compressor power input! vs. temperature of water delivered was

plotted.

(,%"rim"nt 3& -roduction o+


15/33

$. 7ll necessary readings were recorded into the experimental data sheet.

(,%"rim"nt 4 & (stimation o+ t!" (++"ct o+ $om%r"ssor -r"ssur" atio on


16/33

(,%"rim"nt 1& "t"rmination o+ -o"r In%ut: "at ut%ut and $o"++ici"nt o+

-"r+ormanc".

$oo'in Wat"r >'o at": >1 ?@ 41.2

$oo'in Wat"r In'"t "m%"ratur": 5 o$@ 26.3

$oo'in Wat"r In'"t "m%"ratur": 6 o$@ 31.7

$om%r"ssor -o"r In%ut W@ 197

"at ut%ut kJ/min@ 45.576

$-- 0.47

.

(,%"rim"nt 2& -roduction o+ "at -um% -"r+ormanc" $ur)"s )"r a an" o+

ourc"s and "'i)"r# "m%"ratur".

im" minut"s@@ t 0 t15

$oo'in Wat"r >'o at":

>1 ?@80 60 40 80 60 40

$oo'in Wat"r In'"t

"m%"ratur": 5 [email protected] 26.8 26.8 26.8 26.8 26.7

$oo'in Wat"r ut'"t

"m%"ratur": 6 [email protected] 30.9 32.4 30.2 31.0 32.3

$om%r"ssor -o"r In%ut

W@198 199 200 196 197 200

16


17/33

(,%"rim"nt 3& -roduction o+ 'o at": >2 ?@ 18.8 18.9

"+ri"rant -r"ssur" o@ -1:barabs@ 3.2 3.1

"+ri"rant -r"ssur" i!@ -2:barabs@ 8.0 8.0

"+ri"rant "m%"ratur": 1 o$@ 7.3 6.3

"+ri"rant "m%"ratur": 2 o$@ 34.7 34.5

"+ri"rant "m%"ratur": 3 o$@ 31.4 31.2

"+ri"rant "m%"ratur": 4 o$@ 20.5 20.4

$oo'in Wat"r >'o at": >1 ?@ 40.3 40.4

$oo'in Wat"r In'"t "m%"ratur" o$@ 26.6 26.6

$oo'in Wat"r In'"t "m%"ratur" o$@ 32.4 32.2

$om%r"ssor -o"r In%ut W@ 201 200

(,%"rim"nt 4 & (stimation o+ t!" (++"ct o+ $om%r"ssor -r"ssur" atio on


18/33

"+ri"rant -r"ssur" o@ -1:barabs@ 3.1 3.1 3.1

"+ri"rant -r"ssur" i!@ -2:barabs@ 8.1 8.1 8.1

"+ri"rant "m%"ratur": 1 o$@ 6.4 6.5 6.4

8. am%'" $a'cu'ation

Hote / the cooling water and refrigerant water flow rate display is in percentage (G!.

0elow are the formula to convert cooling water and refrigerant flow rate to


19/3319


20/33

(,%"rim"nt 2&

Sample Calculation :Flow rate of 80%

20


21/33

$oo'in

Wat"r

>'o rat"

?@

In'"t

"m%"ratur

"

0$@

$-!%-o"r

W@kJ/min@ J@

80 26.8 4.9 196 57.4 861210

60 26.8 4.5 197 53.2 798120

40 26.7 3.9 200 47.3 709650

21


22/3322


23/33

(,%"rim"nt 3&

Sample Calculation :Flow rate of 40%

+.+3+$2? bar I +3+.$2? ka

+ I $.+ bar I $+3 ka

23


24/33

2 I E.+ bar I E+3 ka

o +ind t!" -sat&

Sample Calculation : TT ! "#$

o +ind "nt!a'%#: !+

Sample Calculation : TT ! "#$

"m%"ratur" ) -r"ssur" k-a@ (nt!a'%# kJ/k@

1 6.3 358.38 60.378

2 34.5 875.42 100.1325

24


25/33

3 31.2 797.79 95.32

4 20.4 579.31 79.884

Araph showing :xperimental ressure vs. :nthalpy of the results above

Araph showing 'deal ressure vs. :nthalpy of the results above

(n"r# ba'anc" on t!" cond"ns"r&

:inJ:outIK:system

25


26/33

#or ideal rankine cycle,condenser(wI3!

()in")out!L(win"wout!Ihf"hi

()in!L(win"wout!Ihf"hi

:nergy balance on the compressor/

teady flow,

(,%"rim"nt 4&

7t t I +? minutes1

+.+3+$2? bar I +3+.$2? ka

+ I $.+ bar I $+3 ka

2 I E.+ bar I E+3 ka

26


27/33

9. iscussion

The experiment was done to identify the applications of the refrigerator and heat

pump. Refrigerators and heat pumps both apply the vapour compression cycle.although the applications of these machines differ,but the components are essentially

the same. To complete the design of the evaporator unit, a thermodynamic analysis of

27


28/33

the refrigeration cycle must be performed. There are four ma5or components that are

involved in this cycle and that will have an affect on the performance of the system.

These components include the/ evaporator, compressor, condenser, and expansion

valves. The thermodynamic cycle that they create is shown below in the figure below.

7n actual vapor"compression refrigeration cycle differs from the ideal one in several

ways, owing mostly to the irreversibilities that occur in various components, mainly due

to fluid friction(causes pressure drops! and heat transfer to or from the surroundings.The CO decreases as a result of irreversibilities.

28


29/33

(,%"rim"nt 1&

#rom this experiment, we have identified the power input ,heat output and

coefficient of performance needed where the values are 197 W: 45.576 kJ/min:and0.47 respectively using the formulas of

and the ob5ective was achieved.

The coefficient of performance (CO! decrease with increasing temperature. o in

order to increase CO;s value, we should decrease the temperature. 7t the end of this

part, we managed to determine the power input, heat output and coefficient of

performance of a vapour compress on heat pump system.

(,%"rim"nt 2&

#rom the graphs in the calculation;s section, we can see that the energy efficiency

of the heat pump is greatly affected by the temperature of the water being heated. The

graph shown that the greater the temperature rise, the harder the work for the

compressor thus the lower the temperatures of the heated to be water, the higher the

energy efficiency becomes.

7fter the calculation of the COs values, we plotted the pump performance curves

of CO vs. delivered water temperature, %&vs. delivered water temperature, and

compressor vs. delivered water temperature. 0ased on our observation, in the first

graph of which CO vs. delivered water temperature, it shown that the CO&values

decrease with temperature which mean that the values depends on temperature. The

second graph of which %&vs. delivered water temperature, shown a similar pattern

29


30/33

with the first graph and it;s the same for the third graph showing that CO, %&and

compressor decreases with increasing temperature.

0y the end of this part of the experiment, we managed to produce the performanceof heat pump over a range of source and temperature using CO, %&and compressor.

(,%"rim"nt 3&

Comparing both diagrams in the theory section (experiment $!1 it clearly showed

that the experimental vs. h graph was way off from the ideal one probably due to

several factors contributing to it. The differences from the actual and the ideal results

of a refrigeration cycle are due to the assumptions made. Calculations with the ideal

refrigeration cycle include the following1

'rreversibilityMs within the evaporator, condenser, and compressor are ignored1

Nero frictional pressure drops1

&eat losses either from the pipes to the surroundings are not considered1

Compression process is isentropic 1

The calculations were made based on the experimental result1 but in which it does

not includes irreversibility, pressure drops due to friction, at variation of pressure

across the refrigeration unit. This is due to the non" ideal condition of the unit itself and

the fact that no machine can function at +33G efficiency. The experimental CO will

be less than the CO obtained for the ideal system. The conceptual value of the

Carnot cycle is that it establishes the maximum possible efficiency for an engine cycle

operating between T&and TC. 't is not a practical engine cycle because the heat

transfer into the engine in the isothermal process is too slow to be of practical value.

30


31/33

&owever in this experiment, the e)uation was not achieved due to irreversibilityMs.

This deviation from the theoretical e)uation above can be explained by several errors

on the experiment and also the condition of the apparatus.

(,%"rim"nt 4&

#rom the calculation made, we have identified the volumetric efficiency and the

compressor ratio which is 0.699 and0.38respectively. 6olumetric efficiencies of at

least 3.E are desirable and are achievable. (R7-, +F??! meaning we failed to achieve

the desirable efficiency of the cycle. The compression ratio and volumetric efficiency

were determined.

Bhile doing the experiment1 due to the irregular data obtained, our lab technicianhas told us that there were no more gases in the refrigeration unit we were using.

That probably would be one of the main cause that our data andor graphs plotted

differs much from the one any experimental cycle should be.

10.$onc'usion

#rom practising this experiment, we;ve concluded that the refrigeration unit that was

used doesn;t perform and never did produced any value that can be said to be near

the ideal cycle. The coefficient of performances produced was a bit off from the ideal

one and the volumetric efficiency also does not achieve the desire efficiency . Thus, it

mean that this unit with such condition is not suitable for daily usage either as

refrigerator or as a heat pump.

31


32/33

11."comm"ndation

The error involve in this experiment would be the apparatus conditions and

assumptions made of the e)uipment.

The reading must be made sure to stabilie before the experiment starts so that we

can minimalie the discrepancies in the data obtained1

To enable the unit operate as nearly the same as the ideal cycle, irreversibilityMs

such as pressure drop due to friction and heat output to the surrounding should be

minimal1

The heat output to the surrounding can be reduced by insulating the exposed pipes

especially the one connected to the condenser and evaporator1

7void the refrigeration unit from being exposed to open air in which it can cause

discrepancies in the calculation and data1

#ollowing the procedures precisely and not in a rush so that an accurate data can

be achieved.

12."+"r"nc"s

'. Cengal,unas, and =ichael 0oles. Thermodynamics/ 7n :ngineering

7pproach. &ighstown/ =cAraw &ill, +FFE.

''. mith, P. =., 6an Hess, &. C., 7bbott, =. =. 8'ntroduction to Chemical

:ngineering Thermodynamics9, =cAraw"&ill 0ook Company, ?th edition +FFD,

pp 2F?"$+.

32


33/33

'''. =ills, 7.#. 80asic &eat and =ass Transfer9, 'rwin, +FF?.

'6. =umovic *., antamouris =., @7 &andbook of ustainable 0uilding *esign and

:ngineering/ 7n 'ntegrated 7pproach to :nergy, &ealth and Operational

erformance@, Cromwell ress, 233F.

6. http/www.idhee.org.ukrenewablesheatpumps.html

6'. http/www.acr"news.commasterclassprint.aspQidIDD$

6''. http/www.heatpumpcentre.orgenaboutheatpumpsheatpumpperformanceid

ordefault.aspxF (,%"rim"nt 2& !"or#@

6'''. http/mariapolis.comfiles&eatpumpandRefrigertor.pdf

'S. corona, Porge. $ 7pril 2334.efrigeration e&periment# -nited tate 7merika /

an #rancisco tate -niversity chool Of :ngineering, $ 7pril 2334.

13.A%%"ndic"s

exp 1 - refrigeration unit

Documents