# Numerical Simulation of Vapour Compression Refrigeration System

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#### Numerical Simulation of Vapour Compression Refrigeration System

1Kalpesh Patil, 2Gauri Thorat

1,2 Fr CRIT, Vashi, Mumbai, Maharashtra E-mail: kalpesp3@ymail.com

3Mathewlal T

Mechanical Engineering Department

3Fr CRIT, Vashi, Mumbai, Maharashtra

Abstract Simulation analysis of vapour compression cycle is carried out. Numerical simulation model of the system is developed, coupling simulation models of compressor, in MATLAB. Result presented shows the influence of different parameters (condenser temperature, evaporator temperature and refrigerant type) on the performance of the system. Refrigerants, R22 and R134a are considered for the analysis. The objective is to analyse the system under various parameters in order to enhance it.

Keywords-Numerical Simulation, Performance Analysis, Evaporator Temperature, Condenser Temperature, Refrigerant.

1. INTRODUCTION

A vapour compression refrigeration system comprises of four components: compressor, evaporator, condenser and expansion device. The Vapour Compression Refrigeration System is an improved type of air refrigeration system using a liquid refrigerant as medium. Fig. 1 shows the schematic diagram of vapour compression refrigeration system.

The refrigerant entering the compressor as saturated vapour is compressed to higher pressure and temperature. The saturated vapour then is passed through a condenser, which condenses it into liquid. Heat is rejected by the circulating refrigerant which is carried away by air. The condensed liquid refrigerant, in saturated state, is next passed through an expansion valve, which results in reduction in pressure and temperature.

Fig. 1. Schematic diagram of vapour compression refrigeration system[1]

A numerical simulation model of the vapour compression system is developed coupling simulation model for compressor. The model is developed for the study of performance parameters on the system and performance curves are plotted, showing the influence of different aspects.

Refrigerants, R22 and R134a are considered for the analysis. The objective is to analyse the system under various parameters in order to enhance it.

Systematic review of the topic have been carried out, Sharad Choudhary[2] was successful in simulating a VCR model and was able to evaluate the mass flow rate (m), refrigeration effect (RE), compressor work (Wc), volumetric efficiency () and coefficient of performance (C.O.P) of the whole refrigeration system based on specific input parameters and varying other input parameters. Baskaran et al.[3] performed an analysis on vapour compression refrigeration system with various refrigerant mixtures of R152a, R170, R600a and R290. From their results, the alternative refrigerants except R431a (which is a combination of R152a, R290 at 29% and 71% respectively) have a slightly higher performance than R134a at the condensation temperature at 50C and evaporator temperature ranging between -30C and 10C.Dhumal [4] et al. investigated the influence of various expansion devices on the performance of a refrigerator using R407C as the refrigerant. He found out that capillary tube with diameter of 0.50 shows 90% increase in compressor work with only 50% increase in refrigeration effect. Andrew Alleye[5] has successfully fabricated an experimental setup with a dual evaporator andR134a as refrigerant. Further, he mathematically modeled the system using MATLAB/Simulink Thermosys library.

2. NUMERICAL SIMULATION MODEL

The numerical simulation model of a vapour compression refrigeration system includes many thermodynamic relations. It is simulated on the Matlab platform. The following assumptions are made for analysis of the system.

1. Clearance ratio of the compressor is 5%

2. Evaporator temperature ranges from 40C to 120C

3. Condenser temperature ranges from 420C to 500C

4. Losses are neglected in the system Following thermodynamics relations[6] are used:

1. Refrigeration Effect

RE = p h4 (1)

2. Work done by the compressor,

Wc = p p (2)

3. Coefficient of Performance of the system

COP = (p h4) / ( p p) (3)

4. Volumetric efficiency of the compressor

= 1 + k [ k * (v1/v2) ] (4)

Where,

p= enthalpy of refrigerant at the outlet of evaporator p= enthalpy of refrigerant at the inlet of condenser p= enthalpy of refrigerant at the outlet of condenser h4= enthalpy of refrigerant at the inlet of evaporator v1= specific volume of refrigerant at the inlet of compressor

v2= specific volume of refrigerant at the inlet of condenser

k= clearance ratio of the compressor

The program is coded using MATLAB Software[7]. Based on mathematical calculations, graphs are generated in the graphical user interface. It displays the performance characteristic curves for refrigeration effect, work done by the compressor, volumetric efficiency of the compressor and coefficient of performance against evaporator temperature as shown in Fig. 2.

Fig .2. Graphical User Interface in MATLAB

3. SIMULATION ANALYSIS

Based on the numerical simulation model, following graphs are plotted to observe the performance of the system by

the template will do that for you.

1. Varying the evaporator temperature for different fixed Condenser Temperature (42C, 44C, 46C, 48C and 50C)

2. Varying the evaporator temperature for different refrigerants (R22 and R134a) at fixed Condenser temperature (460C)

3. Obtaining appropriate operating temperature range of the evaporator, at fixed condenser temperature (460C) and refrigerant (R22)

Case1: Variation in the Evaporator temperature for different fixed Condenser temperature[8].

The influence of the evaporator temperature and different fixed condenser temperatures is numerically studied. Fig 3, Fig. 4, Fig. 5 and Fig. 6 show graphs obtained for Refrigeration effect (KJ/kg), compressor work (KJ/kg), volumetric efficiency of compressor and COP of the system against evaporator temperature, respectively.

Fig. 3. Graph of refrigeration effect versus evaporator temperature

Fig. 4. Graph of work done by compressor versus evaporator temperature

Fig. 5. Graph of coefficient of performance versus evaporator temperature

Fig. 6. Graph of volumetric efficiency of compressor versus evaporator temperature

The comparative results shows that for evaporator temperature range of 4C to 12C

1. Refrigeration effect increases with the increase in evaporator temperature and decreases with condenser temperature.

2. Work done by compressor decreases with the increase in evaporator temperature and increases with condenser temperature.

3. C.O.P increases with the increase in evaporator temperature and decreases with increase in condenser temperature.

4. Volumetric efficiency of compressor increases with the increase in evaporator temperature and decreases with increase in condenser temperature

Change in performance parameters for different fixed condenser temperature and evaporator temperature range of 40C to 120C is given in Table 1.

TABLE 1

146.2

96

 Condenser temperature (C) 42 44 46 48 50 Refrigeration effect at evaporator temperature (KJ/Kg) 4 C 154.441 151.751 149.037 143.529 12 C 157.133 154.443 151.729 148.988 146.221 Change in refrigeration effect (%) 1.743 1.774 1.806 1.84 1.876 Work Done at evaporator temperature (KJ/Kg) 4 C 25.9785 27.2232 28.4588 29.6764 30.8829 12 C 19.6617 20.8761 22.0819 23.2703 24.4476 Change in Work Done (%) 24.315 23.332 22.407 21.587 20.838 COP at evaporator temperature 4 C 5.9449 5.5743 5.2369 4.9297 4.6475 12 C 7.9918 7.3981 6.8712 6.4025 5.981 Change in COP (%) 34.312 32.718 31.207 29.876 28.693 Volumetric Efficiency at evaporator temperature (%) 4 C 91.2595 90.5521 89.8076 89.0231 88.1992 12 C 94.1945 93.6382 93.0527 92.4358 91.7879 Change in Volumetric Efficiency (%) 3.216 3.408 3.613 3.833 4.069

Case 2: Variation in the Evaporator temperature for different refrigerants at fixed Condenser temperature[9].

The influence of the evaporator temperature for different refrigerants- R22 and R134a is numerically studied. Fig. 7, Fig. 8, Fig. 9 and Fig. 10 shows graphs obtained for Refrigeration effect (KJ/kg), compressor work (KJ/kg), COP of system and volumetric efficiency of compressor(%) against evaporator temperature.

Fig. 7. Graph of refrigeration effect versus evaporator temperature

Fig. 8. Graph of work done versus evaporator temperature

Fig. 9. Graph of coefficient of performance versus evaporator temperature

Fig. 10. Graph of volumetric efficiency versus evaporator temperature

The comparative results shows that for evaporator temperature range of 4C to 12C

1. The work done for compressing R22is higher than R134a.

2. The refrigeration effect produced by R22 is higher than R134a.

3. C.O.P of the system is almost same for both R22 and R134a.

4. Volumetric efficiency of compressor for R22 is higher than R134a.

Change in performance parameters at fixed condenser temperature 460C, for different refrigerants and evaporator temperature range of 40C to 120C is given in Table 2.

TABLE II

 Refrigerant used R-22 R-134a Refrigeration effect at evaporator temperature (KJ/Kg) 4 C 149.037 135.58 12 C 151.729 140.09 Change in refrigeration effect (%) 1.806 3.326 Work Done at evaporator temperature (KJ/Kg) 4 C 28.4588 26.2279 12C 22.0819 20.5085 Change in Work Done (%) 22.407 21.807 COP at evaporator temperature 4 C 5.2369 5.1693 12 C 6.8712 6.8308 Change in COP (%) 31.207 32.142 Volumetric Efficiency at evaporator temperature (%) 4 C 89.8076 87.3526 12 C 93.0527 91.4592 Change in Volumetric Efficiency (%) 3.613 4.701

Case 3: Obtaining appropriate operating temperature range of the evaporator, at fixed condenser temperature and refrigerant.

The influence of the evaporator temperature on performance of the system, at a particular condenser temperature is numerically studied. The condenser temperature is 460C and the refrigerant used is R22. Fig. 11 shows graph for Refrigeration effect (KJ/kg), compressor work (KJ/kg) and COP of the system against evaporator temperature. Fig. 12 shows graph for the work done and volumetric efficiency of compressor against evaporator temperature. Based on the above two graphs, appropriate operating temperature range of evaporator is obtained.

Fig. 11. Graph of intersection of refrigeration effect, work done and coefficient of performance curves

Fig. 12. Graph of intersection of work done and volumetric efficiency curves of compressor

4. CONCLUSION

The analysis conducted in three different cases is discussed in the respective section. The conclusion from each case is also written. With reference to the analysis in each case it can be concluded that this simulation model can be easily adapted to different refrigerants.

The present study also shows the impact of different parameters which need to be optimized so as to increase the performance. All the observations and the readings in this simulation will be verified with actual data from the proposed experimental set up.

REFERENCES

1. Typical single stage vapour compression refrigeration http://en.wikipedia.org/wiki/Vapor-compression_refrigeration

2. Sharad Choudhary, Performance Analysis of Reciprocating Refrigerant Compressor, International Journal of Science and Research (IJSR), June 2013.

3. Baskaran et al., Simulation Analysis of Compression Refrigeration Cycle with Different Refrigerants, International Journal of Engineering and Innovative Technology (IJEIT), April 2013.

4. Dhumal et al., Air Conditioning Principles and Systems, International Journal of AdvancedEngineering Technology E-ISSN 0976-3945, 4th edition, Pearson, New York, 2003.

5. Andrew Alleyne, Ralph M. and Catherine V. Fisher, Modelling and Control of VapourCompression Cycles, University of Illinois, Urbana- Champaign.

6. Prof. U.S.P. Shet , Prof. T. Sundararajan and Prof. J.M . Mallikarjuna , Lessons on Refrigeration and Air Conditioning, Mechanical Engineering, IIT