Refrigeration Unit.docx

7/23/2019 Refrigeration Unit.docx

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UNIVERSITI TEKNOLOGI MARA

FAKULTI KEJURUTERAAN KIMIA

ENGINEERING CHEMISTRY LABORATORY

(CPE453)

NO Title All!"te# M"$%&

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3 A11e/#i: 5TOTAL MARKS

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This experiment demonstrated the general operation of vapor compression heat pump.

In order to determine the power input and coefficient of performance of the heat pump, the

temperature and pressure of water and refrigerant are observed. The process cycle of heat

pump is clearly illustrated in pressure enthalpy diagram. The compressor pressure ratio and

volumetric efficiency are also calculated. The objectives of this experiment successfully

achieved. This experiment is successful achieved although the experiment do not produce a

good result since the execution of the procedure is not fully accurate.

.

INTRODUCTION.

A refrigeration unit is a unit composed of several machineries that can transfer heat

from a low-temperature region to a high-temperature region. Normally heat can only be

transfer from a high temperature region to low, so to reverse this process, a refrigerator is

needed. efrigerator consists of four main components which are! compressor, evaporator,

expansion valve and condenser. "ach component wor#s together to perform a series of

process. The process includes a cycle of refrigerant and a flow of cooling water.

In the experiment, the refrigeration unit used is $%&T"' (echanical )eap *ump

+(odel ")/0. The device is design to give understanding to the user on how refrigeration

process wor#ed.

The $%&T"' (echanical )eat *ump +(odel )"/0 is a bench top unit with all

components and instrumentations mounted on the sturdy base. The heat pump consists of a

hermetic compressor, a water-cooled plate heat exchanger, a thermostatic expansion valve

and a water heated plate heat exchanger. The arrangements of the components are in a

manner similar to many domestic air- water heat pumps where they are visible from the front

of the unit.

1uring the operation, slightly superheated refrigerant +-23a0 vapor enters the

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

and the hot vapor then enters the water cooled condenser. )eat is given up to the cooling

water and the refrigerant condenses to li4uid before passing to the expansion valve. 5pon

passing through the expansion valve, the pressure of the li4uid refrigerant is reduced. This

causes the saturation temperature to fell to below that the atmospheric. Thus, as it flows

through the evaporator, there is a temperature difference between the refrigerant and the

water being drawn across the coils. The resulting heat transfer causes the refrigerant to boil,

and upon leaving the evaporator it has become slightly superheated vapor, ready to return to


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the compressor.

The temperature at which heat is delivered in the condenser and the evaporator is

controlled by the water flow rate and its inlet temperature. Instrumentations are all provided

for the measurement of flow rates of both refrigerant and cooling water, power input to thecompressor and all relevant temperatures.

AIMS/OBKECTIVES.

i. Experiment 1

The objectives of this experiment is to determine the power input, heat output and coefficient

of perfomance.

ii. Experiment 2

The objectives of this experiment is to determine the production of heat pump perfomance

curves over a range of source and delivery temperatures.

iii. Experiment 3

The experiment is to determine the production of vapor compression cycle on p-h diagram

nd energy balance study

iv. Experiment 4

The experiment is to study determine the production of heat pump perfomance curves over a

range of evaporating and condensation temperature.

v. Experiment

The objectives of this experiment is to estimate the effect of compressor pressure ratio on

volumetric efficiency.

T!EOR".

A heat pump is a mechanism that absorbs heat from waste source or surrounding to

produce valuable heat on a higher temperature level than that of the heat source. The


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fundamental idea of all heat pumps is that heat is absorbed by a medium, which releases

the heat at a re4uired temperature which is higher after a physical or chemical

transformation.

)eat pump technology has attracted increasing attention as one of the most

promising technologies to save energy. Areas of interest include heating of buildings,

recovery of industrial waste heat for steam production and heating of process water for e.g.

cleaning, sanitation.

6enerally, there are three types of heat pump systems

i0 7losed cycle vapor compression heat pumps +electric and engine driven0ii0 )eat transformers +a type of absorption heat pump0

iii0 (echanical vapor recompression heat pumps operating at about at 899:7

Closed Cycle Vapor Compression Heat Pump

(ost of the heat pumps operate on the principle of the vapor compression cycle. In this

cycle, the circulating substance is physically separated from the heat source and heat

delivery, and is cycling in a close stream, therefore called ;closed cycle


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Figure 1: The closed loop compression cycle

Vapor Compression Heat Pump System Principles

Figure 2: Vapor compression heat pump cycle

T0e !,1/e/t& "$e=

) C/#e/&e$.) C,1$e&&$3) E:1"/&i/ V"l>e4) E>"1$"t$

=our basic processes or changes in the condition of the refrigerant occur in a >apor


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7ompression )eat *ump 7ycle. These four processes shall be illustrated in the most

simplistic way with the aid of above figure.

i# C$mpre%%i$n &r$'e%% ( t

1 t

2 #

The refrigerant at the pump suction is in gas at low temperature and low

*ressure. In order to be able to use it to achieve the heat pump effect

continuously, it must be brought to the li4uid form at a high pressure. The first

step in this process is to increase the pressure of the refrigerant gas by using a

compressor. 7ompressing the gas also results in increasing its temperature.

ii# C$n)en%in* &r$'e%% ( t2 t3 #

The refrigerant leaves the compressor as a gas at high temperature and

pressure. In order to change it to a li4uid, heat must be removed from it. This is

accomplished in a heat exchanger called the condenser. The refrigerant flows

through one circuit in the condenser. In the other circuit, a cooling fluid flows

+normally air or water0, at a temperature lower than the refrigerant.

)eat is therefore transferred from the efrigerant to the 7ooling fluid and as a

result, the refrigerant condenses to a li4uid state +20. This is where the heatingta#es place.

iii# Exp+n%i$n &r$'e%% ( t

3 t

4 #

At *oint +20, the refrigerant is in li4uid state at a relatively high pressure and

temperature. It flows to +30 through a restriction called the flow control device or

expansion valve. The refrigerant loses pressure going through the restriction. The

*ressure at +30 is so low that a small portion of the refrigerant flashes +vapori?es0

into a gaseous. In order to vapori?e, it must gain heat +which it ta#es from that

portion of the refrigerant that did not vapori?e0.

iv# V+p$ri,in* &r$'e%% ( t

4t

1 #

The refrigerant flows through a heat exchanger called the evaporator. The heat

source is at a slightly higher temperature than the refrigerant, therefore heat is

transferred from it to the refrigerant. The refrigerant boils because of the heat it

receives in the evaporator. @y the time it leaves the evaporator +30 it is completely

vapori?ed.


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Understanding the Pressure Enthalpy Diagram

Figure 3: A pictorial representation of a P-H diagram

5sing the chart of -23a efrigerant +=igure 20, we shall attempt to explain the use of it

The 7hart is divided into T)"" areas. These three areas are separated from each other by

the following

a0 $aturated li4uidb0 $aturated vapor line

The area on the chart to the left of the $aturated &i4uid line is called the $5@7%%&"1

region. At any point in the sub-cooled region, the refrigerant is in the &I'5I1 phase and its

Temperature is below $aturation temperature corresponding to its *ressure.

The area to the right of the $aturated >apor line is the $5*")"AT"1 region, and the

refrigerant is in the form of a $5*")"AT"1 >A*%.

The area between the $AT5AT"1 &I'5I1 and the $AT5AT"1 >A*% lines is the


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mixture region and represents the change in phase of the refrigerant between the li4uid and

>apor phases. Thus, at any point between the two saturation lines the refrigerant is in the

form of li4uid-vapor mixture.

The distance between the two lines along any constant pressure line is #nown as thelatent heat of vapori?ationB at that pressure.

The $aturated &i4uid line and $aturated >apor line are not exactly parallel to each other

because the Clatent heat of vapori?ationC varies with the pressure at which the change in

phase occurs.

This change of phase from li4uid to vapor phase ta#es place progressively from &"=T to

I6)T and the change in phase from vapor to li4uid phase occurs from I6)T to &"=T.

At any point on the $aturated &i4uid line, the refrigerant is at $AT5AT"1 &I'5I1 and

at any point along the $AT5AT"1 >A*% &IN", the efrigerant is a $AT5AT"1

>A*%.

The )%ID%NTA& &IN"$, extending across the chart are 7%N$TANT *"$$5" &ines.

The >"TI7A& &ines are &ines of 7%N$TANT "NT)A&*E.

The &ines of 7onstant Temperature varies, depending on the phase stage. It is

almost >"TI7A& in the $5@7%%&"1 region and is *A*A&&"& to lines of 7%N$TANT

"NT)A&*E.

It however changes at the 7"NT" section, since the refrigerant changes state at a

7%N$TANT T"(*"AT5" AN1 *"$$5", the lines of 7onstant Temperature are now,

parallel to constant *ressure line. At the $aturated >apor line, the lines of 7onstant

Temperature changes direction again and upon entering the $5*")"AT"1 >A*%"6I%N, it falls off sharply towards the bottom of the chart.

The "N)A&*E >alues are found on the )ori?ontal scale at the bottom of the chart.

The (agnitudeF of the *ressure in barG(*a is read on the vertical scale at the left side of the

chart.

Temperature values in degrees 7elsius are found adjacent to constant temperature

lines in sub-cooled and superheated regions of the chart on both $aturated &i4uid and


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$aturated &ines.

It is worthwhile to note that the p-h diagram is based on a limb mass of the

refrigerant, the volume given is the specific volume, the "nthalpy is in #H per #g, and the

entropy is in #H per #g per degree of absolute temperature.

%btain the "nthalpy >alues from *-) 1iagram

To obtain the following values, we first refresh our memory from the previous chapter on

a0 =low diagram of a $imple $aturated 7ycleb0 "nthalpy or p-h diagram of -23A, $imple $aturated 7ycle, as shown below!

Figure 4: Flo diagram of a simple saturated cycle


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Figure !: "omparison of to simple saturated cycles operating at di#erent

$apori%ing temperatures &'gure distorted( &)efrigerant-134a(

Figure *a: +,eleton P-H chart illustrating the three regions of the chart and the

direction of phase changing


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Figure *: +,eleton P-H chart shoing oaths of constant pressure. constant

temperature constant $olume. constant enthalpy. and constant entropy

&)efrigerant-134a(

Figure *c: Pressure-enthalpy diagram of a simple saturated cycle operating at a

$apori%ation temperature of 2//F and a condensing temperature of 1///0F

&)efrigerant 134a(


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In recalling, and referring bac# to =igure / and , of a $imple $aturated 7ycle, we now thusobtained the following values

h The "nthalpy at *oint , which is the point where 7ompression *rocessC begins

+This is also where we obtained the Temperature eading, TT for the process0

h8 The "nthalpy at *oint 8, which is the point where C7ompression *rocessC ends.

h2 The "nthalpy at *oint 2, which is the point where C7ondensationC is complete.

+This is also where we obtained the Temperature eading, TT2 for the process0

Thus,

h8 J h2 efrigerating "ffect +$ee figure /0

Khile,

h8 J h )eat of 7ompression +$ee figure /0

Figure : Pressure-enthalpy diagram of a simple saturated cycle operating at a

$apori%ing temperature of 2/oF and a condensing of 1//0F &)efrigerant- 134a(


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Coefcient o Perormance

The 7oefficient of *erformance, +7%*)0 of a heat pump cycle is an expression of the cycle

efficiency and is stated as the ratio of the heat removed in the heated space to the heat

energy e4uivalent of the energy supplied to the 7ompressor.

7%*) )eat removed from heated space G )eat energy e4uivalent of the "nergy supplied

to the compressor.

Thus, for the Theoretical $imple 7ycle, this may be written as

7%*) Heating Effect

Heat of Compression

(h2h3)(h2h1)

A&&ARATUS.


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Figure 8: Unit construction for Mechanical Heat Pump (Model: HE165)

. *ressure switch8. eceiver tan#2. 7ompressor3. 7ondenser/. *ressure transmitter. 7ontrol panelL. "vaporatorM. efrigerant flow meter. Kater flow meter


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&ROCEDURES.

i. -ener+ Oper+tin* &r$'e)re%

A. -ener+ St+rt0Up &r$'e)re%

. The unit and all instruments are chec#ed to ensure they are in proper conditions.8. The water source and drain are chec#ed to ensure they are connected. The water supply is

open and the cooling water flowrate is set as .9 &*(2. The drain hose at the condensate collector is chec#ed to ensure it is connected.3. *ower supply is connected. The main switch is on at the main power and main switch on

control panel./. efrigerant compressor is switch on.when the temperature and pressure is constant, the unit

is ready for experiment.

B. -ener+ St0D$n &r$'e)re%

. The compressor is switched off followed by the main switch and power supply.8. The water supply is closed.

Experiment 1. 6eeral start up procedure is performed.8. The cooling wate r flow rate is adjusted to 39O2. The system is run for /minutes.3. The reading is recorded.

Experiment 2

. The The general start-up was run.8. The cooling water flow rate was adjusted to 9O..2. The system was allowed to run for / minutes.3. All the necessary reading was recorded in the table./. The procedure to 3 was repeated with different cooling water flow rate. +39O and 89O0. All the necessary reading was recorded in the table

.

Experiment 3

. The general start-up was run.8. The cooling water flow rate was adjusted to 39O.2. The system was allowed to run for / minutes.3. All the necessary reading was recorded in the table.

Experiment 4

. The general start-up was run.8. The cooling water flow rate was adjusted to 9O.2. The system was allowed to run for / minutes.


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3. All the necessary reading was recorded in the table./. The procedure to 3 was repeated with different cooling water flow rate. +39O and

89O0. All the necessary reading was recorded in the table.

Experiment

. The general start-up was run.8. The cooling water flow rate was adjusted to 39O.2. The system was allowed to run for / minutes.3. All the necessary reading was recorded in the table.


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RESUTS AND CACUATIONS

E&ERIMENT 1

7ooling Kater =low ate, =T O 39

7ooling Kater =low ate, =T &*( 8

7ooling Kater Inlet Temperature, TT/ :7 29.2

7ooling Kater %utlet Temperature , TT :7 2./

7ompressor *ower Input K /

Cli/ ?"te$ @? $"te (LPM) Cooling water flowrate()

100 : 5 LPM

Re9$ie$"/t @? $"te (LPM) Refrigerant flow rate( )

100 : .2 LPM

He"t +t1+t

.mL

min :1g

1mL :1kg

1000 g :1min

60s 33%*&

T(K)=T()+273.15

Cp@2550=4.18 kJ

kg.K

Q=m Cp dT

0.033kg(4180 Jkg.K)(31.530.3)K

165.53W


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Ce!ie/t 9 1e$9$,"/!e

Wnet,

C!R="esired o#tp#t

Re$#ired inp#t=QL

165.53

165.0

1.0032

E&ERIMENT 2

8 2

7ooling Kater =low ate, =T O 9 39 89

7ooling Kater =low ate, =T &*( 2 8

7ooling Kater Inlet Temperature, TT/ :7 29.8 29.2 29.8

7ooling Kater %utlet Temperature , TT :7 2.2 2.2 22.9

7ompressor *ower Input K 3 / L

)eat %utput K /.L2 89. 2M.82C !R 9.8 .8/ 8.2

PThe calculations are similar to that in "xperiment .


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3. 34 32 36 3. 3.. 3.4 3.2 3.6 33 33.

2.5

23

235

24

245

25

255

22

225

2

25

24

25

2

Power input vs temperature

Temperature !"

Power #nput $"

3. 34 32 36 3. 3.. 3.4 3.2 3.6 33 33.

5

5

.

.5

3

35

4

45

53

.27

362.3

Heat output vs temperature

Temperature !"

Heat output $"


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3. 34 32 36 3. 3.. 3.4 3.2 3.6 33 33.

5

5

.

.5

7.

.5

.3

C%P vs temperature

Temperature !"

C%P

E&ERIMENT 3

efrigerant =low ate, =T8 O .2

efrigerant =low ate, =T8 &*( 9.LL

efrigerant *ressure +&ow0, * @ar

+abs0

8.9

efrigerant *ressure +)igh0, *8 @ar

+abs0

L.

efrigerant Temperature, TT :7 8M.L

efrigerant Temperature, TT8 :7 M8.9

efrigerant Temperature, TT2 :7 M.efrigerant Temperature, TT3 :7 83.L

7ooling Kater =low ate, =T O 39.

7ooling Kater =low ate, =T &*( 8.9

7ooling Kater Inlet Temperature, TT/ :7 29.2

7ooling Kater %utlet Temperature , TT :7 2.

7ompressor *ower Input K /

&$int 1 2 3 4&re%%re (5+r# 8.9 L. L. 8.9


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Temper+tre ( 8M.L M8.9 2. 83.L

Ent+p6 (78/7*# 8LL.L 289./ 8./ 8L3.8L

PAll of the enthalpy value was obtained from the property table of -23a +interpolation0

!2!1!3!1

T2T1T3T1

.2 3.4777777777776 .2752 .4.

.

3

4

5

2

6

.

.

Pressure

Enthalpy &'(&g"

Pressure )ar"

PThe cycle is out of the curve +all of the state is in superheated vapor0


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Figure 9: deal !apor compression c"cle

7ompressor energy balance

hmW

pekeQ

kepehmWQ

=

===

=

0$0$0

)(

7ondenser energy balance

hmhmQ

hmQ

pekeW

kepehmWQ

outin

=

=

===

=

0$0$0

)(

E&ERIMENT 4

8 2

efrigerant =low ate, =T8 O .8 .8 .2

efrigerant =low ate, =T8 &*( 9.LL 9.LL 9.LL

efrigerant *ressure +&ow0, * @ar +abs0 8.9 8.9 8.9

efrigerant *ressure +)igh0, *8 @ar +abs0 L. L. L.

efrigerant Temperature, TT :7 8M.M 8M. 8M.2

efrigerant Temperature, TT8 :7 M8.8 M8.9 M.9

efrigerant Temperature, TT2 :7 29.M 2. 28.9

efrigerant Temperature, TT3 :7 83./ 83.3 83./"ntalphy +*, TT0 #HG#g 8LL.M3 8LL.L 8LL.3


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"ntalphy 8 +*8, TT80 #HG#g 289.2/ 289./ 2./

"ntalphy 2 +*8, TT20 #HG#g 8.M 8.3 8L9.2L

"vaporating Temperature +TT30 :7 83./ 83.3 83./

7ondensing Temperature +TT20 :7 29.M 2. 28.29

7ompressor *ower Input K 2 / 3

)eat 1elivered in 7ondenser +efrigerant0 K 9./ 9./ 9.237%*) .893 .2 .

PAll of the enthalpy value was obtained from the property table of -23a +interpolation0

9.LLL

min Q1000mL

L Qg

mL Qkg

1000 g Qmin

60 s 9.92 #gGs

Trial

' mRh

m+h8-h20

9.92+289.2/-8.M0

9./ #K

7%*)

Heating Effect

Heat of Compression

(h2h3)(h2h1)

321.55268.7321.55276.74

.L


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PThe same calculations are used for Trial 8 and 2.

E&ERIMENT

efrigerant =low ate, =T8 O .

efrigerant =low ate, =T8 &*( 9.LL

efrigerant *ressure +&ow0, * @ar

+abs0

8.9

efrigerant *ressure +)igh0, *8 @ar

+abs0

L.

efrigerant Temperature, TT :7 29.8

7ompressor pressure ratio %#ction press#re of refrigerant

"ischarge press#re of refrigerant !1

!2

2

7.1

9.8M8

>olumetric efficiency &ct#al mass flow rate

Theoretical mass flow rate


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DISCUSSIONS.

B$6e9% +stated that the pressure of gas inversely proportional to the volume of a

container. =rom the results recorded, some calculation have been made in order to #now the

difference value between before and after of the experiment one. These values are very

small and close with the theoretical value, therefore the @oyles


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depressuri?ation approach in this study yield a more reliable result for an example in the

production sector in industries. The molecule in the container affected when the number of

them decreasing slowly as they do not have to collide between them more often. The

depressuri?ation shown that pressure decrease with time and also affecting the temperature.

As the pressure decrease, the temperature also decrease in the system.

Brie: )epre%%ri,+ti$nshown in the graph plotted in result section which is decrease

more linear compared to stepwise. The expansion occur when the pressure of gas increase.

"xpansion of gas decrease as the gas is free to flow out time by time.

R+ti$ v$mecan be determined by manipulating the e4uation of @oyle8 and after manipulate the e4uation ratio

volume can be determine by >8G>**8. This experiment test in three different condition

where first condition the gas is flow from tan# to tan# 8, while gas flow from tan# 8 to tan#

in second condition and both were filled with gas in third condition. The theoretical value is

9.3/ in this experiment where the error or percentage difference was between 9 and -9.

There must be environmental factors that affect the stability of pressure and temperature or

random mista#e during experiment. The percentage error is high due to some error during

conducting the experiment. $ome of air probably left from chamber due to not properly close

the valve or before the experiment, the gas did not left out completely from the chamber.

Determin+ti$n $: r+ti$ $: e+t '+p+'it6using the expression of the heat capacity ratio and

it gives the ./M3. The theoretical value of this experiment is .3. The deviation which now

is e4ual to 8O. The deviation is due to measurement error. The actual intermediate

pressure supposed to be lowered that the measured one. 5nfortunately the error occur due

to heat loss and sensitivity of pressure sensors. $upposed, the intermediate pressure ta#en

as the lowest pressure at the moment the valve is closed. $ince the percentage difference is

more than 9O, the experiment can be declared as failed.


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COCUSIONS.

In conclusion, the experiment was aimed at determining the properties of measurement G*>T

according to the @oyle


28/29

RE;ERENCES.

"ngineering $ciences M8 *>T (easurement And *roperties %f a $imple 7ompressible

$ubstances. +n.d0. etrieved from

httpGGsites.fas.harvard.eduGSesMGhandoutsGlab9*>Tf9/v.pdf

7harlesFs &aw. +8990. etrieved from $par#notes

httpGGwww.spar#notes.comGtestprepGboo#sGsat8GchemistryGchapter/sectionM.rhtml

7harlesFs &aw. +n.d.0. etrieved from how stuff wor#s

httpGGscience.howstuffwor#s.comGdictionaryGphysics-termsGcharles-law-info.htm

7alculating *>T *roperties. +n.d0. etrieved from

httpGGpetrowi#i.orgG7alculating*>Tproperties
http://sites.fas.harvard.edu/~es181/handouts/lab01_PVT_f05_v9.pdfhttp://www.sparknotes.com/testprep/books/sat2/chemistry/chapter5section8.rhtmlhttp://science.howstuffworks.com/dictionary/physics-terms/charles-law-info.htmhttp://petrowiki.org/Calculating_PVT_propertieshttp://www.sparknotes.com/testprep/books/sat2/chemistry/chapter5section8.rhtmlhttp://science.howstuffworks.com/dictionary/physics-terms/charles-law-info.htmhttp://petrowiki.org/Calculating_PVT_propertieshttp://sites.fas.harvard.edu/~es181/handouts/lab01_PVT_f05_v9.pdf


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A&&ENDI.

. *ressure switch8. eceiver tan#2. 7ompressor3. 7ondenser/. *ressure transmitter. 7ontrol panel

L. "vaporatorM. efrigerant flow meter7 Kater flow meter

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