Thermodynamic Analysis of Vapor Compression Refrigeration

The assignment involves a thermodynamic analysis of vapor compression refrigeration, focusing on the impact of power input and evaporator temperature on the system's effectiveness. The document provides a comprehensive overview of the topic, including references to relevant studies and research papers.

LABORATORY REPORT:
COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES
STUDENT NAME
STUDENT NUMBER
GROUP NUMBER
COURSE TITLE BEng (Hons) Building Services Engineering
MODULE TITLE / CODE Mechanical Services / UBLMPB-30-3
LECTURER NAME
DATE OF EXPERIMENT
DATE OF REPORT SUBMISSION

I declare that the coursework submitted is my own work and has not (either in whole or
part) been submitted towards the award of any other qualification either at UWE or
elsewhere. I have fully attributed/referenced all sources of information used during the
completion of my assignment, and I am aware that failure to do so constitutes an
assessment offence.
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Laboratory Report: COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES 1

CONTENTS
Page
1. INTRODUCTION 1
2. THEORY & OBJECTIVES …
3. METHOD …
4. RESULTS …
5. DISCUSSION …
6. FURTHER RESEARCH …
7. REFERENCES …
8. APPENDIX …
1. INTRODUCTION
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Laboratory Report: COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES 2

Cooling of buildings is one of the major factors which construction of building materials
will have to consider [1]. To achieve the best vapor compression cycle should be able to
achieve the best coefficient of performance during the cooling process. Better vapor
compression cycle is able to indicate the effectiveness of the refrigerator systems. Refrigeration
machines are always used in cooling of buildings [2]. These machines are able to employ
vapors-compression cycles to achieve the cooling effect. A volatile fluid is mostly used to
achieve the cooling effect. This fluid is able to change phase at low temperature in order to
absorb heat and cool the loads. In addition, in order to achieve the cooling effect, the
refrigerator is able to change the fluid pressure and achieve the temperature at which phase-
change point. Two major key factors which are considered for the cooling effect is the energy
supply to the cooling load and the size of the cooling load. The Coefficient of Performance
(CoP) is defined as the ratio between these two quantities and thus able to measure the
efficiency of the systems [3]. Therefore the evaporation and condensation temperatures will
have a close relation with the CoP. This report will be able to investigate the relationship
between CoP and evaporation/condensation temperatures at which the cycle operates [4].
Theoretically, any cooling system, refrigeration systems and condensers temperature are
guided by the size and type of the system components and temperature required for cooling
load and heat sink available.
2. THEORY & OBJECTIVE
Refrigeration is defined as a process of heat removal from a region or state and substance in
order to maintain low temperature, by transferring the heat to another region. The heat transfer
on the refrigerator is based on the vapor compression cycles. The performance of the heating
and refrigerator systems is measured in terms of CoP [5]; which is expressed as follows;
CoPR = {Desired output/ required input} = (cooling effect/work input)
= QL/Wnet, in
The power input is depended on situations of the equipments. The power can be measured at
different points and therefore this means that the CoP will depend on the location where the
power is measured at. Under this experiment, different condenser designs with varying
evaporator loadings are used to analyze the efficiency of CoP [6]. Most importantly, the CoP is
depended on the evaporator cooling load, QL and the power input cycle to the system, W [9].
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Laboratory Report: COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES 3

The power used in calculation of CoP may be different depending on the location it is measured.
For instance, shaft power may be used, and this can be calculated from data involving the
torque T and angular velocity ω.
Therefore: WS = T ×ω
WS =(F × r) where motor speed nm = nc R
In the R713 rig, the torque arm radius, r = 0·165 m and the belt pulley ratio, R = 3.08
Thus: WS =(0 165F)⋅
The power in the systems can therefore be derived from different sections [7]. After getting the
power, the theoretical limit point of the CoP of the system operating a reversed Carnot is given
as;
CoPCarnot =
The main objective of this report will be to analyze the relationship between CoP and evaporator
temperature for the condenser which is recorded at different temperatures.
3. METHOD
Equipment
Hilton R715 Refrigeration Unit
Procedure
1. First a suitable condenser was selected with saturation temperature adjusted to 30oC.
The corresponding saturation pressure for the Hilton R715 was determined from
thermodynamic property table.
2. Next, the unit was connected and ran and the power of the electrical heater was set in
the evaporator to about 200W.
3. Condenser water flow rate was adjusted to achieve the required condenser saturation
pressure. The conditions were then allowed to settle.
4. The following details were recorded;
t4 refrigerant temperature entering evaporator (˚C)
PE evaporator pressure (kPa)
PC condenser pressure (kPa)
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Laboratory Report: COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES 4

F dynamometer spring balance force (N)
QE evaporator load (W)
We motor input power (W)
nc compressor rotational speed (RPM)
5. Next, the evaporator load was increase in 200W steps and the above data recorded. In
addition, when the condenser pressure drifted as the evaporator load was increased, minor
adjustments on the cooling water flow to steady the pressure at its initial value was carried out.
6. In addition, the experiment was repeated with an increased condenser temperature of 40 oC.
In the experiment, Hilton R715 Refrigeration Unit was used. The following diagram represent
the different parts and combination of the unit;
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Laboratory Report: COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES 5

Provide discussion of discrepancies with actual process, compare between the
theoretical forecast and the observed experimental behavior. Make clear assumptions
and identify possible errors.
4. RESULTS
After the experiment, the following results were achieved.
First set
Power input-
200W,
Evaporator point
36oC
Power input-
400W,
Evaporator
point 36oC
Power input-600W,
Evaporator point
36oC
Power input-800W,
Evaporator point
36oC
T1 7.1 20 6.5 12.6
T2 40.6 47.4 50 50
T3 35.7 35.5 36 36.5
T4 -20.8 -12.1 -4.8 1.3
T5 18.8 18.9 18.9 19.1
T6 33.5 28.2 26 26.5
Motor input (W) 416 440 475 480
Tachometer
(rpm)
836.9 831 830 826
Torque (N) 12 13 14 15
Pressure
(kN/m3)
900 880 800 880
Water flow
(g/sec)
4 12 22 28
Refrigerant flow
(g/sec)
4 7 8 13
Second set
Power input-
200W,
Evaporator point
Power input-
400W,
Evaporator
Power input-600W,
Evaporator point
44oC
Power input-800W,
Evaporator point
44oC
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Laboratory Report: COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES 6

44oC point 44oC
T1 -4.8 10.8 7 6.3
T2 64 59 57.4 55
T3 44 43.7 44.9 45.6
T4 -15.58 -3.4 2 2.6
T5 19.3 18.5 19.5 19.2
T6 43.6 38.1 38.4 40
Motor input (W) 463 530 535 540
Tachometer
(rpm)
833 824 817 812
Torque (N) 14 15 16 16
Pressure
(kN/m3)
1150 1000 1000 800
Water flow
(g/sec)
2 8 9 7
Refrigerant flow
(g/sec)
7 11 13 14
5. DISCUSSION
The change of power input is able to influence the CoP and other outputs of the refrigerator [8].
The motor input is able to increase with the increase on the power input in the system.
Regardless on the evaporator temperature, the motor input is able to increase when power input
is increased. In addition, another factor which affects the motor input is the temperature change
for the system. Operating the system at 36 oC is able to yield a lower motor input each moment.
The increase of the temperature to operate the system at 44 oC is able to show an increase of
the motor inputs at each step. In addition, another factor which is affected by the change in the
power input is the tachometer revolutions per minute. Increasing the power input has an inverse
impact on the tachometer [8]. The tachometer is decreasing in each set of the experiment
carried when the input power is increased. The tachometer is important since it is able to
influence the angular velocity of the system. This means that the angular velocity, which will be
increasing. And therefore since torque multiplied by angular velocity gives the shaft power, it is
justified that the motor output is increasing.
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Laboratory Report: COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES 7

Moreover, from the experiment it is clear that the torque is as well affected by the change on
power input. The torque force is increasing with the increase in the power input in both
experiments. Therefore, it can be conclude that the power input increase requires more torque
force to operate the system. Change in the evaporator temperature has little or no change on
the torque. This can be noted from the trend of the torque values in the first set of experiment
and the second one. The changes in the two experiments are following the same trend and are
almost the same. In addition, increasing the input power has direct influence on the water flow.
This is because the power increases the power which moves the water around. In addition, the
increase in flow means that the cooling influence is enhanced [9]. The increase in water flow is
a positive indicator since it helps the refrigerator to increase its effectiveness. The power input
therefore makes the water flow to increase and therefore enhance the reduction of the
temperature. In addition, the refrigerant flow is also affected by the change on the power input.
The increase in power input is able to lead to an increase on refrigerant flow within the system.
This can be related to the increase on the power which drives the fluid through. The increased
flow is a good aspect of the refrigerator since it increases the rate of cooling the system. In
conclusion, it is clear that the increase on the power input has a positive impact on the CoP.
This is because increasing the power is able to increase the effectiveness of the refrigerator.
The CoP is able to measure the effectiveness of the system. The increased flow of the coolant
fluids is able to increase the effectiveness of cooling effect.
6. FUTURE RESEARCH
The change on the power input is able to affect the different refrigerator inputs. This included
the effectiveness of the refrigerator which is measured in terms of CoP. Therefore through the
change of the input power, the analysis of the CoP was clearly carried out and the aim of the
experiment was achieved. In addition, the change of the evaporator temperature is seen to have
impact on the CoP. The effectiveness of the refrigerator is affected by this change in
temperature and the analysis of the impact was achieved through the experiment.
The effectiveness of the refrigerator system is largely depended on the cooling system [10]. The
analysis of the CoP is important but relying is on the input power might not be such effective.
Future research needs to be based on the changes done on the coolant fluid and its influence
0on CoP. In addition, the further researches must be able to look at the other factor which
affects the effectiveness of the refrigerator. In addition, change on the evaporator density should
be analyzed to determine whether it is able to influence CoP. This will ensure that high
effectiveness of the refrigerating materials is achieved and enhance CoP.
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Laboratory Report: COEFFICIENT OF PERFORMANCE OF VAPOUR-COMPRESSION CYCLES 8

7. REFERENCES
[1] Radermacher, Reinhard, and Yunho Hwang. Boca Raton, FL: Taylor & Francis,
(2005). Vapor Compression Heat Pumps with Refrigerant Mixes. New Haven and
London: Yale University Press.
[2] Arora, Ramesh C. (2011). Refrigeration and Air Conditioning, New Delhi: PHI
Learning,. Print
[3] James W. C (2005). Thermodynamic Analysis of Subcooling and Superheating
Effects of Alternative Refrigerants for Vapour Compression Refrigeration Cycles. John
Wiley & Sons, Ltd,. Internet resource.
[4] Hundy, G H, A R. Trott, and T Welch. (2016).Refrigeration, Air Conditioning and
Heat Pumps. , New Haven and London: Yale University Press.
[5] Nikolaidis, Christos. (1997). A Computer Study of Multi-Stage Vapour Compression
Refrigeration Cycles by the Exergy Method. , London: Icon Books.
[6] Kaushik, Shubhash C, Sudhir K. Tyagi, and Pramod Kumar. Cham: Springer, (2017).
Finite Time Thermodynamics of Power and Refrigeration Cycles, Internet resource.
[7] Grace, Iain N., (2000). Modelling the Performance and Dynamics of Vapour
Compression Refrigeration Systems, Print.
[8] Wayne, C. (2011). Real-time Simulation of Vapour Compression Cycles. , New
Haven and London: Yale University Press.
[9] Sheppard, P A, and François N. Frenkiel.New York: Academic Press, (2008)
Atmospheric Diffusion and Air Pollution: Proceedings of a Symposium Held at Oxford,..
London: Icon Books.
[10] Hundy, Guy. (2008). Refrigeration and Air-Conditioning, Burlington: Elsevier,
Internet resource.
8. APPENDIX
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