INTERNATIONAL JOURNAL OF ADVANCED RESEARCH … IMPROV… · International Journal of Advanced Research in Engineering and ... International Journal of Advanced Research in ... refrigeration

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN

0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME

187

PERFORMANCE IMPROVEMENT BY REDUCING COMPRESSOR

WORK OF R-134A AND R22 USED REFRIGERATION SYSTEMS BY

USING TWO-PHASE EJECTOR

K.GANESH BABU B.Tech., M.Tech -R&A/C.

Assistant Professor, Department of Mechanical Engineering,

Sagar Institute of Technology, Chevella, Ranga Reddy – 515002,

Andhra Pradesh, India.

K.RAVI KUMAR B.Tech., M.Tech -R&A/C.

Assistant Professor, Department of Mechanical Engineering,

All- Habeeb College of Engineering, Chevella, Ranga Reddy – 515002,


Dr. Md. AZIZUDDIN M.E. (Mech), Ph.D. (Osm.,)

Professor & Head Department of Mechanical Engineering,

Royal Institute of Science & Technology, Chevella, Ranga Reddy – 515002,


ABSTRACT

Research works evidenced that using expansion device in vapour compression refrigeration system giving less efficiency and degraded system performance. Present work R-134a and R22 are used as working fluids, Using Engineering Equation Solver (EES) software version 6.883. Computer simulation is carried out in between Simple vapour compression system & 1-Dimensional Two-phase ejector used vapour compression system.

Under the optimal values of Ejector area ratio (Ar) = 14, entrainment ratio (U) = 0.53, nozzle efficiency (nn) = 85%, diffuser efficiency (nd) = 85% at operating conditions of Evaporator temperature Te=-15°C, condenser temperature Tc = 30°C. The COPs of Ejector used vapour compression (EVCR) system 4.649 for R134a and 4.433 for R22, at the same operating conditions, simple vapor compression system COP 3.733 for R134a. COP Improvement 19.70 % for Ejector used refrigeration system than simple vapour compression refrigeration system.

Keywords: Vapour compression refrigeration system; R134a; Ejector; EES software; COP

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN

ENGINEERING AND TECHNOLOGY (IJARET)

ISSN 0976 - 6480 (Print) ISSN 0976 - 6499 (Online) Volume 4, Issue 3, April 2013, pp. 187-193 © IAEME: www.iaeme.com/ijaret.asp Journal Impact Factor (2013): 5.8376 (Calculated by GISI) www.jifactor.com

IJARET

© I A E M E



188

I. INTRODUCTION

Electrical energy consumption has become a worldwide research topic because Refrigeration

and Air-conditioning systems consuming electrical energy approximately 15%. Ejector used vapour compression refrigeration system has some special advantages such as the simplicity in construction, high reliability and low cost compare to other refrigeration systems.

Throttling loss and Higher power consumption for compressor are the major losses in a conventional vapour compression refrigeration system. Various devices have been held instead of the conventional devices like Capillary tube, Thermostatic expansion valve. Ejector is a device that uses a high-pressure fluid to pump a low-pressure fluid to a higher pressure at a diffuser outlet. Its low cost, no moving parts and ability to handle two-phase flow without damage make it attractive for being the expansion device in the refrigeration system.

To reduce the throttling losses of vapour compression cycle we replace the throttling device. Ejector as an expander in that, the process is isentropic. By using ejector devices we are able to reduce the throttling looses and reduces the load on evaporator so that the COP of the combined compression refrigeration cycle is increases. The descriptions of ejector are as given below

1.1 Two phase ejector:

Ejector is an expander which uses an expansion device in vapour compression cycle and replaces the throttling loss by replacing throttling device in vapour compression cycle. The appropriate installation of the ejector in vapour compression cycle increases the COP of the refrigeration system by raising the compression suction pressure to a level higher than that in the evaporator and consequently, to reduce the load on the compressor and motor.

In the ejector geometry there are three sections of ejector 1. Motive Nozzle, 2. Mixing tube, 3. Diffuser section.

In Ejector used Vapour compression refrigeration cycle comprises of the following Ejector, Evaporator, Compressor, Condenser, Separator, etc. Figure.1 shows the configuration of ejector. Ejector is an expression device which replaces the throttling valve in order to reduce the throttling losses of expansion device. The ejector is installed at the outlet of the condenser (6 to 1), and the motive fluid (liquid from the condenser) enters into the nozzle at a relatively high pressure. Reduction of the pressure of the liquid in the nozzle provides the potential energy for conversion to kinetic energy of the liquid. The driving flow entrains vapour out of the evaporator. The two phases are mixed in mixing chamber (at point 2) and leave it after a recovery of pressure in the diffuser part of the ejector (at point 3). The liquid portion is directed to the evaporator through a small pressure-drop expansion device (7 to 8) while the vapour portion enters the compressor suction (3 to 4). The lines from points 4, 5, 6 are a series process in the compressor and the condenser. The lines from points 7, 8, 9 are a series process in the expander and the evaporator. Points 6 and 1 are the state of the flow at the exit of the primary nozzle and in the mixing area (point 2) of the ejector while point 2–3 is a compression process in Diffuser. The appropriate installation of the ejector increases COP of the refrigeration system by raising the compression suction pressure to a level higher than that in the evaporator and consequently, to reduce the load on the compressor and motor.



189

III. SIMULATION ANALYSIS

Based on the Thermodynamic analysis, a steady-state simulation program for the vapour

compression refrigeration cycle, using EES software (Klein and Alvarda (2006)) is developed.

3.1 Solution methodology in engineering equation solver (EES) (Klein and Alvarado (2007))

EES is a software package developed by Dr. Sanford Klein of the University of Wisconsin. EES incorporates the programming structure of C and FORTRAN with a built-in iterate, thermodynamics and transport property relations, graphical capacities, numerical integration, and many others useful mathematical functions. By grouping equations there are to be solved simultaneously, EES is able to function at a high rate of computational speed. Ammonia-water mixture properties are calculated in EES using the correlation developed by Ibrahim and Klein (1993). There are two major differences between EES and exiting numerical equations solving programs. First, EES automatically identifies and groups equations that must be solved simultaneously. This feature simplifies the process for the users and ensures that the solver will always operate at optimum efficiency. Second, EES provides many built in mathematical and thermo physical property functions useful for engineering calculations. The basic function provided by the engineering equation solver (EES) is the numerical solution of the non-linear algebraic and differentials equations, EES provides built in thermodynamics and transport property functions for many fluids including water, dry and moist air. Included in the property database are thermodynamics properties for H2O-LiBr and NH3-H2O mixture. Any information between quotation marks [“] or [{}] is an optional comment. Variable names must start with a letter. A code containing a good library of working fluid properties suitable for heat pumps is the Engineering Equations Solver (EES). Here the user must write the equations governing the cycle and make sure the set is well-defined. In the case of a non-linear set of equations, the user must check the results to make sure that the mathematical solutions are also a physical One.

3.2 Simulation analysis on Vapour compression refrigeration system:

3.2.1 Simulation was performed to evaluate the COP of vapour compression cycle with the following assumptions

1. The refrigerant was at all times in thermodynamic quasi-equilibrium. 2. Characteristics and velocities were constant over cross section 3. Negligible pressure drop. 4. There is no wall friction. 5. The processes in compressor, expansion valve area assumed to be adiabatic. 6. Saturated state at the evaporator and the condenser outlet.

3.2.2 Input parameters for Vapour compression refrigeration system simulation: Evaporator temperature (Te) : -15 0C Condenser temperature (Tc) : 30 0C Mass flow rate (m) : 1/60 (kg/sec) Refrigerant : R-134a



190

3.2.3 Flow chart for Vapor compression system simulation analysis:

3.2.4 Vapour compression refrigeration system simulation results: Evaporator temperature (Te) = -15 ˚C Condenser temperature (Tc) = 30 ˚C Evaporator pressure (Pe) = 1.64 bar Condenser pressure (Pc) = 7.706 bar Compressor inlet enthalpy (h1) = 241.5 kJ/kg Compressor outlet enthalpy (h2) = 281.1kJ/kg Evaporator inlet enthalpy (h4) = 93.58 kJ/kg Mass flowrate (m) = 0.01667 kg/sec Coefficient of performance (COP) =

= ( )

( )

1 4

2 1

m h h

m h h

− −

= ( )

( )

0.01667 * 241.5 93.58

0.01667 * 281.1 241.5

− −

= 1 4 7 . 9 2

3 9 . 6

= 3.733



191

3.3 Simulation was performed to evaluate the ejector used vapour compression cycle with the following assumptions:

1. The refrigerant was at all times in thermodynamic quasi-equilibrium. 2. Characteristics and velocities were constant over cross section (1-dimensional model). 3. All fluid characteristics are uniform over the cross section after complete mixing at the exit of

the mixing tube. 4. There is no external heat transfer to the system. 5. There is no wall friction. 6. Negligible pressure drop. 7. The processes in compressor, expansion valve and ejector area assumed to be adiabatic. 8. Saturated state at the evaporator and the condenser outlet. 9. One dimensional flow in the ejector.

3.3.1 Flow chart for Ejector used vapour compression refrigeration system simulation analysis:

3.3.2 Input parameters for Ejector used system simulation analysis:

Evaporator temperature ( ) : -15 ºC

Condenser temperature ( ) : 30 ºC Ejector convergent Nozzle efficiency ( ) : 85%

Ejector diffuser efficiency ( ) : 85% Ejector area ratio (Ar) : 8 Entrainment ratio (U) : 1 Refrigerant : R134a



192

Graph.3 Nozzle efficiency (nn=10 to 100 %) Vs COP

Graph.4 Diffuser efficiency (nn=10 to 100 %) Vs COP

26.626.38

26.1625.95

25.7325.52

25.3125.1

24.924.69

23

24

25

26

27

10 20 30 40 50 60 70 80 90 100

Com

press

or w

ork

(W

c) in

kJ/k

g

Diffuser efficiency (nd)

Diffuser efficiency(nd) Vs Compressor work (Wc) in kJ/kg

Compressor

Work (Wc) in kJ/kg

Graph.5 Diffuser efficiency (nd) Vs Compressor work (Wc in kJ/kg)

Above Graph.3 shows the decreasing of COP by increasing the nozzle efficiency. Diffuser efficiency is mainly affecting the COP of the system, because the diffuser efficiency increasing means the pressure of the refrigerant from diffuser inlet to outlet pressure is increasing with respect to increase in efficiency shown in Graph.4. But it is going to affect on the refrigerating effect i.e. enthalpies (h9-h8) starts to decrease, again the expansion valve throttling losses coming to matter. For better results the nozzle efficiency is little bit less than or equal to diffuser efficiency.

V: CONCLUSIONS

In the present simulation analysis the results has been computed for vapour compression refrigeration cycle & ejector used vapour compression refrigeration cycle. The effect of the geometry of the ejector Area ratio with the refrigerant R134a has been analyzed. The maximum COP = 4.649 is



193

obtained for optimum area ratio whose value is around Ar = 14 for ejector used refrigeration system because, at this area ratio the COP is maximum and compressor pressure ratio (Pr) is minimum.

Optimal entrainment ratio(U) = 0.53 because the compressor pressure ratio (Pr) = 2.362 low compared to simple vapour compression system compressor pressure ratio (Pr) = 4.698, the quality of vapour refrigerant at outlet of ejector x3=0.4366 is optimal at entrainment ratio (U) = 0.53 compare to quality of vapour refrigerant at outlet of ejector x3 = 0.8331 at entrainment ratio (U) = 2. The simulation analysis results shows that for a given evaporator temperature (Te) = -15˚C and the condenser temperature (Tc) =30 ˚C, the vapour compression refrigeration cycle COP = 3.733 is less than that of the ejector used vapour compression refrigeration cycle COP = 4.649. The system performance mainly depends on the diffuser efficiency, because the diffuser efficiency increase is increasing the pressure at the outlet of diffuser. This pressure increase is decreasing the pressure ratio of the compressor. Compressor pressure ratio decreases the compressor work also decreases. If work decreases the COP of the system will increase. The system performance also depends on the nozzle efficiency. The nozzle efficiency increase is decreasing the pressure at the outlet of nozzle. This pressure decrease is increasing the pressure ratio (Pr) of the compressor. Compressor pressure ratio increases the compressor work (Wc) also increases. If work increases the COP of the system will decrease. For better results the nozzle efficiency is little bit less than or equal to diffuser efficiency. The performance increase of the ejector used vapour compression refrigeration system is 19.70%.

VII: REFERENCES:

1. Chen, LT. (1988) ‘A new ejector–absorber cycle to improve the COP of an absorption

refrigeration system’, Applied Energy, Vol.30, pp.37–51. 2. Elbel, S., Hrnjak, P. (2006) ‘Experimental validation of a prototype ejector Designed to reduce

throttling losses encountered in transcritical R744 system operation’ International journal of refrigeration, Vol.32, pp.411-412.

3. Huang, B.J., Hu, S.S., Lee, S.H. (2005) ‘Development of an ejector cooling system with thermal pumping effect’ International journal of refrigeration, Vol.29, pp.476-484.

4. Klein, S.A., Alvarda, F., (2003) Engineering Equation Solver, Version 6.883. F-chart software, Middleton, WI.

5. Li, D., Groll, A. (2005) ‘Transcritical CO2 refrigeration cycle with ejector expansion device’, International Journal of Refrigeration, Vol. 28, pp.766–773.

6. Refrigeration and Air-conditioning by R.S.Kurmi 7. Refrigeration and Air-conditioning by Domkundwar, Arora, Domkundwar. 8. Dr. Ashok G. Matani And Mukesh K. Agrawal, “Performance Analysis Of Vapour

Compression Refrigeration System Using R134a, Hc Mixture And R401a As Working Medium” International Journal Of Mechanical Engineering & Technology (IJMET) Volume 4, Issue 2, PP: 112 – 126, ISSN PRINT : 0976 – 6340, ISSN ONLINE : 0976 - 6359

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INTERNATIONAL JOURNAL OF ADVANCED RESEARCH … IMPROV… · International Journal of Advanced Research in Engineering and ... International Journal of Advanced Research in ... refrigeration