International Journal of Scientific & Engineering Research, Volume 5, Issue 5, May-2014 929
ISSN 2229-5518
Performance Evaluation of Vapour Compression
Refrigeration System With
Three Layer Zig -Zag Shaped Evaporator
K.Usha Rani M.Tech | Guide:Dr. B.Chandra Mohana Reddy Assistant Professor |
Dept. of Mechanical Engineering J.N.T.U College of Engineering Anantapuramu (Dist), Andhra Pradesh – 515002 | Dept. of Mechanical Engineering JNTU Anantapur, Anantapur (Dist) Andhra Pradesh – 515 002 |
This paper presents performance evaluation of the vapor compression refrigeration system with three layer zigzag evaporator. The main objective in the present work is to verify the performance of a domestic refrigerator of capacity 165 liters, R-600a as refrigerant with three layer zigzag shaped evaporator and comparing with that of the existing system. This evaporator assembly maximizes the refrigerating effect. An attempt made to verify the performance of the system by replacing the a single evaporator coil into three layers of zigzag shape coil to find the coefficient of performance (COP) and refrigeration effects. The proposed system with three layer zigzag evaporator designed and analysis carried out and studied the performance of the refrigerator.
Vapor compression Refrigeration system (VCR) is an improved type of air refrigeration system. The ability of certain liquids to absorb enormous quantities of heat as they vaporize is the basis of this system. The coefficient of performance of a refrigeration system is the ratio of refrigerating effect to the compression work; therefore the coefficient of performance can be increased by increasing the refrigerating effect or by decreasing the compression work. The Vapour compression refrigeration system is now-a-days used for all purpose refrigeration. It is generally used for all industrial purposes from a small domestic refrigerator to a big air-conditioning plant.
Basic components of VCR:
1).Compressor 2).Condenser 3).Expansion valve and
4).Evaporator
The refrigeration effect (output) is produced at evaporator in VCR. There are few methods of improving the COP for a Domestic Refrigerator which is operated by VCR. Increasing the refrigeration effect is one of the best way to improve the
performance of VCR.
In this paper, it is observed that the refrigeration effect can
also be increased by modifying the circulation of liquid refrigerant in the evaporator tube. The arrangement of tube is in three layers in zigzag manner, two layers are parallel and horizontal at top and one layer is vertical at bottom of evaporator. Further, this arrangement can also increases the cooling space/refrigeration zone in the refrigerator
In vapor compression refrigerating system basically there are two heat exchangers. One is to absorb the heat which is done by evaporator and another is to remove heat which is done by condenser and the heat of compression added in the compressor and condenses it back to liquid which is done by condenser. This project focuses on heat absorption in the evaporator and investigated the performance of three layer zigzag shaped evaporator using these evaporator in the present domestic refrigerator. In this project the evaporator surface and the length has been increased in zigzag form In order to know the performance characteristics of the vapor compression refrigerating system the temperature and pressure gauges are installed at each entry and exit of the component. Experiments are conducted on the evaporator. Different types of tools are also used like tube cutter to cut the tubes and tube bender to bend the copper tube to the required
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ISSN 2229-5518
angle. Finally the domestic refrigerator is fabricated as for the requirement of the project. Specifications of the domestic refrigerator for existing system and proposed systems tabulated below.
The following procedure is adopted for experimental setup of the vapor compression refrigeration system
The domestic refrigerator is selected, working on vapor compression refrigeration system. Pressure and temperature gauges are installed at each entry and exit of the components. Flushing of the system is done by pressurized nitrogen gas.
R 600a refrigerant is charged in to the vapor
compression refrigeration system by the following process:
The systematic line diagram for charging is shown in the fig. it is necessary to remove the air from the refrigeration unit before charging. First the valve V2 is closed and pressure gauge P2 , vacuum gauge V are fitted as shown in the fig. the valve V5 is also closed and valves V1 , V4, V6 and V3 are opened and the motor is started thus the air from the condenser receiver and evaporator is sucked through the valve V1 and it is discharged in to atmosphere through the valve V6 after compressing it in the compressor the vacuum gauge V indicates sufficiently low vacuum when most of the air is removed in the system. The vacuum reading should be at least 74 to 75 cm of Hg. If the vacuum is retained per above an hour it may be concluded that the system is free from the air. After removing the air the compressor is stopped and valves V1 and V6 are closed, the valves V5 , V2 and V7 of the refrigerant cylinder are opened and then the compressor is started whenever the sufficient quantity of refrigerant is taken in to the system which will be noted in the pressure gauges. The compressor is stopped. The valves V 7 and V5 are closed and valve V1 is opened the refrigerant cylinder is disconnected from the system the pressure gauge is used to note
the pressure during the charging the system.
Specifications of three layer evaporator
Number of layers = 3
Radius of bend 1 = 2.54 cm Radius of bend 2 = 1.90 cm Pitch between bend 1 = 12.7 cm Pitch between bend 2 = 15.24cm
Number of turns = 9
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Fig 1 . Charging of refrigeration system
Leakage tests are done by using soap solution, In order to further test the condenser and evaporator pressure and check purging daily for 12 hours and found that there is no leakages which required the absolutely the present investigation to carry out further experiment. Switch on the refrigerator and observation is required for 1 hour and take the pressure and temperature readings at each section. The performance of the existing system is investigated, with the help of temperature and pressure gauge readings. The refrigerant is discharged out and condenser is located at the inlet of the capillary tube. Temperature and pressure gauge readings are taken and the performance is investigated. The readings are tabulated for three layer condenser. The tests were conducted and calculated values tabulated below .
1. At first layer =-2°C
2. At second layer = -2°C
3. At third layer =0°C
4. Ambient temperature =370C
PROPOSED SYSTEM OF THE REFRIGERATIOR
FIG 2.EXPERIMENTAL DOMESTIC REFRIGERATOR
S. N O | PARAMETERS | EXIST ING SYST EM | PROPO SED SYSTE M |
1. | suction temperature(0C),T1 | 28 | 24 |
2. | discharge temperature(0C),T2 | 71 | 68 |
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The performance of vapour compression system by using three layer with zig-zag shaped evaporator and compare with the existing system. The existing system coefficient of performance is 5.81 and three layer evaporator has been increased with an coefficient of performance is to 6.6
.
Fig shows the compressor work with the existing system. It is observed that compressor work is decreased with the existing system. Because, here the suction pressure is increased and discharge pressure is decreased, so the compressor work and compressor power decrease when compare proposed system with the existing system.
Fig show is observed that it net refrigeration increased with existing system. When suction pressure is increased and discharge pressure is decreased area of cooling space is increased from p-h chart and experimentally the evaporator surface and length also increased because of this reason net refrigeration effect is increased.
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shows the mass flow rate with existing system. It is
observed that it mass flow rate decreased with existing system.
Shows the compressor power with exiting system. It is observed that it decreasing compressor with existing system, because of suction pressure increased and discharge pressure decreased.
.
It is seen that the at the performance of the refrigeration system as the compressor work decreases with increase in coefficient of performance and decrease in heat rejection
.when the evaporator performance is increased and
compressor work is decreased the performance of the system is also increased because it is the ratio of the heat
absorb from the system to compressor work.
Shows the heat rejection ratio. It is observed the heat rejection ratio has been decreased because of the net refrigeration effect is increased and greater than the heat rejection compared with the existing system.
• In my present work an experiment set is prepared for both existing and proposed system. In the proposed system three layer zig-zag shaped evaporator is used. The capacity of the domestic refrigerator is 165Lts.
• Experiments are conducted for existing system and proposed systems. In both systems 600a refrigerant is used.
• In the proposed system the compressor work is less than compressor work of existing system. The percentage of reduction in compressor work is 9.
• In the proposed system the heat to be rejected in the
condenser is greater than the heat to be rejected in existing system. The percentage of heat reduction in condenser is 1.3.
• In the proposed system the COP is greater than the COP of the existing system. The percentage of increase in COP is 13.
• From the above results, It is concluded that, the
proposed system with 600a is giving the better performance than the existing system with 600a. Hence the proposed is best suitable for the 165lts of domestic refrigerator.
APPENDIX
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1. Refrigeration and Air Conditioning -Stocker
2. Principles of Refrigeration-Ray.J.Dossat
3. Refrigeration and Air Conditioning-Manohar Prasad
4. Refrigeration and Air Conditioning-B.L.Ballany
5. Refrigeration and Air Conditining-S.C. Arora & Domukundawar
6. Basic Refrigeration and Air Conditining-P.N.
Ananthanarayan
7. Heat Transfer-J.P.Holman
8. Refrigeration and Air Conditioning- C.P. Arora
9. Technical Handbook for non ac applications-Shriram refrigeration industries
10. Refrigeration service manual – Kelvinator of India ltd.,
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