International Journal of Engineering, Management & Sciences (IJEMS) ISSN-2348 –3733, Volume-2, Issue-5, May 2015
Theoretical Performance Analysis of Vapour Jet Ejector for R 134a Sonia Rani, Gulshan Sachdeva Abstract— In the present paper performance of refrigerant R134a is discussed throughout an ejector for low temperature heat source for refrigeration and air–conditioning applications. The proposed system performance has been compared with Carnot cycle working at same operating conditions with influence of condenser, generator, and evaporator temperature on performance of Vapour Jet Refrigeration (VJR) system. Furthermore, the effect of ejector efficiency also discussed at constant operating conditions. The design conditions were evaporator temperature (5-15˚C), condenser temperature (30-45˚C) and generator temperature (75-80˚C). For calculation purpose mathematical equations are developed and simulation results are obtained with EES (Engineering Equation Solver). The present results depicts that the performance of the ejector highly depend on operating conditions on the performance of ejector system. Index Terms—Ejector, R134a, Refrigeration.
Mathematics, Performance,
I. INTRODUCTION Refrigeration and air conditioning is essential extensively in world requirement of different applications like hotels, buildings, hospitals, manufacturing of ice, domestic refrigerators, deep freezers, automobiles, heating and ventilation. Refrigeration is a process of maintains of system temperature below than environment temperature by providing continues supply of energy in form of electricity. Generally vapour compression refrigeration system (VCRS) is employed for meet refrigeration purposes in addition to abundant amount of electricity providing to mechanical compressor [1]. As we know to meet huge amount of electricity demand fossils fuels are used for energy generation. By burning coal and fossils fuels we meet mainly two problems as follows: One is emission of CO2 gas which is dangerous for environment. The other is increasing global warming potential due to emission of chlorine atom from refrigerants. As a result, the European commission Regulation 2037/2000, installed on 1 October 2000, a program to control all the ozone depleting materials and all HCFCs (hydro chlorofluorocarbons) will be forbidden by 2015 [2]. One Manuscript received February 20, 2015. Sonia Rani , School of Renewable Energy and Efficiency, National Institute of Technology, Kurukshetra, India, Gulshan Sachdeva, Mechanical Engineering Department, National Institute of Technology, Kurukshetra, India,
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solution is to overcome this problem adoption of clean energy. However, we can use waste heat or solar heat for refrigeration and air conditioning. For utilizing of solar heat or waste heat Eejector air conditioning is attractive choice. Advantage of elimination of mechanical compressor no moving part except pump makes it more reliable in addition to reduced maintenance cost. In the present study Munday and Bagster theory is use according to which assumption of two discrete streams was considered [3]. The motive stream flow through primary nozzle and suction stream flow through secondary nozzle attains mixing of both fluids in mixing section at constant pressure. Immediate mixing shock wave generate results to subsonic velocity of mixed stream which can be obtained by intersection of Fanno and Rayleigh lines proceeding through diffuser [4]. At outlet of diffuser mixed stream velocity is negligible. In 1942, the constant pressure mixing theory of ejector was developed by Keenan and Neuman .They assumed constant pressure mixing ejector and many researchers used their study for further research work [5]. Sun and Eames described a simulation model for ejector refrigeration applications using working fluid as refrigerant R123 in place of R11. Their results showed that R123 is good alternative for R11 in air conditioning purposes. They also studied the effect of variable geometry on the performance of system at variable operating conditions for optimum results [6]. Nehdi et al. [7] performed experiments on supersonic ejector and found result for optimum designing of ejector with Refrigerant R11. Diswas and wongwises experimentally investigated the performance of ejector expansion refrigeration cycle without expansion valve of evaporator and their results showed improvement in coefficient of performance relative to conventional cycle [8]. Alexis predicted the main cross-section of ejector for refrigeration applications [9]. Salvaraju and Mani developed computer program to investigate the effect of specific heat of working fluid and friction on constant area mixing chamber [10]. II. EJECTOR PERFORMANCE AND MATHEMATICAL MODELING An ejector is a device which is used to entrain low pressure fluid by high pressure fluid without any mechanical power input. In fig.1 demonstrate the working of ejector system in which high pressure superheated vapour raised in generator (6). Now these vapours passes through ejector (2) in
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Theoretical Performance Analysis of Vapour Jet Ejector for R 134a
converging- diverging nozzle, entraining low pressure vapour refrigerant into ejector from evaporator (1). The mixing of two streams is done in mixing chamber at constant pressure. After this mixed fluid passes through diffuser where pressure is recover at expense of enthalpy at stagnation condition of velocity at outlet. Fluid is come into condenser (3) to reject heat with surrounding at constant temperature and pressure. In condenser high pressure vapour refrigerant change into high pressure liquid refrigerant. After condensing it will divide into two streams. One enters into evaporator via capillary tube (4) reducing pressure at constant enthalpy. Another one flows into generator (6) before passing through pump (5) to raises the pressure of liquid refrigerant.
Fig. 3: Mollier chart of R134a
Momentum of fluid is assumed to be conserved at mixing section. The mathematical equations which are used for calculate the performance of ejector system as follows:
Vx1 Vx 2 (1 )Vm
Energy balance equation can be applied at mixing section
(1)
(2) h6 h2 (1 ) h3 Where is entrainment ratio for flow (ratio of mass of
secondary fluid to mass of primary fluid) At nozzle section energy balance equation can be applied: Va12 2(h6 ha1 ) (3)
Fig. 1: Schematic diagram of vapours jet ejector air conditioning
Where ha1 is obtained from the equations:
s6 s (T6 , P6 ) sas s fas xas ( s gas s fas )
(4)
has h fas xas (hgas h fas )
(5)
n ( h6 ha1 ) / ( h6 has )
(6)
ha 2 h fa 2 xa 2 (hga 2 h fa 2 )
(8) (9)
By application of energy balance equation between 2 and a2: Va 22 2(h2 ha 2 ) (7)
Fig. 2: Schematic diagram of ejector
A computer program is developed to calculate the performance of system for range of parameters based on four basics equations. a) Conservation of mass b) Conservation of momentum c) Conservation of energy d) Isentropic process Following assumptions are made for calculation purpose. a) Flow through ejector is one dimensional, steady state and adiabatic. b) Primary and secondary fluid is at zero velocity at inlet and outlet of ejector. c) Isentropic flow through nozzle and diffuser. d) Primary and secondary fluid mixed at constant pressure. e) Normal shock occurs at end of constant area mixing chamber [11].
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Applied energy balance equation between section 3 and m: (10)
Vm2 2(h3 hm )
Value of pressure Px is assumed lie between Pm and P3. Similarly value of velocity at point Y can be calculated as: hm h fm xm (hgm h fm ) (11)
sm s fm xm ( sgm s fm ) s ys sm s fys x ys ( sgys s fys )
(12)
hys h fys x ys (hgys h fys )
(13) (14)
my (hm hys ) / (hm hy )
(15)
Vy V fy x y (Vgy V fy )
(16) (17)
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International Journal of Engineering, Management & Sciences (IJEMS) ISSN-2348 –3733, Volume-2, Issue-5, May 2015
m taken 2400 , Pd=Py and by intersection of Rayleigh and A Fanno lines Td can be calculated.
(18)
hd h( Pd , Td )
(19) (20)
Vd V ( Pd , Td )
(21)
s3 s sd s (T3 s Pd )
(23)
h3 s (T3 s , Pd )
(24)
Where K1, K2 are constant and can be calculated by applying same equation at y state. At diffuser following equation are used: (22) sd (Td , Pd )
my (hm hys ) / (hm hy )
(25)
h3 (T3 , P3 )
(26)
depend on condenser and evaporator temperature. By varying the operating conditions for ejector we study the various effects. A. Effect of evaporator temperature on Entrainment ratio In figure 4.1 variation of entrainment is seen with changing condenser and evaporator temperature by considering effect of Px. The range of evaporator temperature is taken from 5-15˚C and condenser temperature 30-45˚C. From graph it depicts that at optimum evaporator temperature maximum value of entrainment ratio is found. Similarly there is condenser temperature at which maximum flow entrainment ratio can be calculated. Temperature and pressure of generator is kept fixed. Value of entrainment ratio varies from 0.09-0.4.
0.5 Te-15
Entrainment ratio
For constant cross-section area some assumptions are
Te-12 Te -5
0.4
0.3
By using above equation performance parameters can be calculated. 0.2 For VJR system coefficient of performance can be obtained by using following equations: 0.1 a) The fluid at exit of evaporator in saturated vapour condition. 0.0 b) The fluid at outlet of condenser in saturated liquid 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 condition. P c) Fluid flowing through capillary tube is isenthalpic. Fig. 4.1: Variation of entrainment ratio with evaporator temperature d) The fluid at outlet of generator is in superheated B. Effect of evaporator and condenser temperature on COP vapour condition. The COP of system is highly influenced by Condenser and e) No heat losses in pipe. evaporator temperature. Figure 4.2 illustrated that by Heat absorbed in evaporator: (27) increasing evaporating temperature performance is increases. Qe me ( h2 h1 ) Maximum COP is found to be 0.76. The variation in Heat supplied by generator, performance is 0.45-0.76 with changing evaporator Qg mg (h6 h5 ) (28) temperature 4-12 ˚C. The condenser temperature variation is Work done by pump 34-42˚C. The COP of system is increases with decreasing the W p mg (h5 h3 ) (29) condenser temperature. COP of system is calculated as
COP
(h2 h5 )
(30)
( h6 h4 )
The Carnot COP of system is given by:
COPc
(Tg Tc )(Te ) (Tg )(Tc Te )
(31)
From the above equation performance of VJR is found and compared with Carnot COP.
Coefficient of performance (COP)
x
1.8 Tc-34 Tc-36
1.6
Tc-38 Tc-40
1.4
Tc-42
1.2
1.0
0.8
0.6
III. RESULTS
2
The performance of ejector is mainly depending on the entrainment ratio. We have to calculate entrainment ratio by mathematical equation by iterative process which is highly
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4
6
8
10
12
14
Te
Fig. 4.2: Effect of condenser temperature under different evaporating temperature on performance of system
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Theoretical Performance Analysis of Vapour Jet Ejector for R 134a
C. Effect of evaporator and condenser temperature on Carnot COP Similarly same effect are seen on Carnot performance in figure 4.3, it depicts that Carnot COP is highly influenced by condenser and evaporator temperature. Maximum performance obtained is 1.7. We found that performance of ejector is low as comparison to Carnot performance. Variation in performance is 0.8-1.7 by changing evaporator and condenser temperature 4-12 ˚C respectively. 0.9 Tc-34
Coefficient of performance (COP)
Tc-36 Tc-38
0.8
Tc-40
In the present study, for ejector refrigeration system a computer program is developed using R134a refrigerant. The main motive of work is to found the entrainment ratio for constant area ejector and performance of jet refrigeration. Theoretical study is done to compare the performance of jet ejector with Carnot COP. The entrainment ratio obtained is 0.09-0.4 for evaporator temperature 5-15˚C. The maximum Carnot COP is 0.8-1.7 and for VJR is 0.47-0.76. Ejector efficiency has no much effect on performance of system. The condenser and evaporator temperature has great impact on performance and entrainment ratio. By increasing generator pressure COP of system increases. As we seen performance of system is less as compare to Carnot.
Tc-42
REFERENCES
0.7
C. P. Arora (2000). “Refrigeration and Air conditioning”2nd edition; New Delhi: Tata McGraw Hill publishing company limited. [2] (2015) The UNEP website. [Online] http://ozone.unep.org/new_site/en/montreal_protocol.php [3] Khalil A, Fatouh M, Elgendy E ( ), “Ejector design and theortical study of R134a ejector refrigeration cycle”, International Journal of Energy, 34, 1684-1698. [4] Huang BJ, Chang JM, Wang CP and Petrenko VAA (1999). “1-D analysis of ejector performance”, J. Refrigeration, 22, 354-364. [5] Keenan J H and Neumann E P (1942). “A simple air ejector”, Journal of Applied Mechanics, 64, 75-82. [6] Sun D, Eames I (1996) “Performance characteristics of HCFC-123 ejector refrigeration cycles”, International Journal of Energy, 20, 871-885. [7] Nehdi E, Kairouni L and Bouzaina M (2007) “Performance analysis of the vapour compression cycle using ejector as an expander”, International Journal of Energy Research, 31, 364-375. [8] Diswas S, Wongwises S (2004). “Experimental investigation on the performance of the refrigeration cycle using a two phase ejector as expansion device”, International Journal of Refrigeration, 27, 587-594. [9] Rogdakis E. D, Alexis G.K, “Design and parametric investigation of an ejector in an air-conditioning system”, Applied Thermal Engineering, vol.20, pp.213-226, 2000. [10] Selvaraju A, Mani A, “Experimental investigation on R134a vapour ejector refrigeration system”, International Journal of Refrigeration, vol.29, pp.1160-1166, 2006. [1]
0.6
0.5
0.4 3
4
5
6
7
8
9
10
11
Te
Fig. 4.3: Effect of condenser temperature under different evaporating temperature on performance of system
D. Effect of generator pressure on COP From figure 4.4 we found that performance of system increases as generator pressure and evaporator temperature increases. Value of COP rises from 0.57-0.68 with variation in evaporator temperature 5-15 ˚C and generator pressure 38-41 bar. By keeping the condenser temperature constant at 40˚C, effects of generator pressure are observed. Thus we conclude that generator pressure has directly impact on performance of system. 0.70
Coefficient of performance (COP)
III. CONCLUSION
Sonia Rani, Perusing Mtech from NIT Kurukshetra in School of Renewable energy and Efficiency department. Her major field of work is Ejector based refrigeration and air-conditioning. She has published paper in International conference. Email address: Sonia.bishiyar@gmail.com
Te - 5 T - 10
0.68
e
Te - 15 0.66 0.64 0.62
Dr. Gulshan Sachdeva received his PhD degree in 2010 from NIT Kurukshetra, Haryana (India).He is assistant professor in NIT Kurukshetra in department of mechanical engineering. His work focus mainly on Computational Fluid Dynamics: CFD tool for the analysis and design of heat exchanger by Numerical Programming and FLUENT software, Refrigeration and Air conditioning: development of refrigerant for the vapor compression systems, Development of efficient Solar systems for the Air conditioning and general Use. Email address: gulshansachdeva@nitkkr.ac.in
0.60 0.58 0.56 37.5
38.0
38.5
39.0
39.5
40.0
40.5
41.0
41.5
Pg
Fig. 4.4: Effect generator pressure under different evaporating temperature on performance of system
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