International Journal of Engineering, Management & Sciences (IJEMS)ISSN-2348 3733, Volume-2, Issue-5, May 2015

47 www.alliedjournals.com

Abstract In the present paper performance of refrigerant

R134a is discussed throughout an ejector for low temperatureheat source for refrigeration and airconditioning applications.The proposed system performance has been compared withCarnot cycle working at same operating conditions withinfluence of condenser, generator, and evaporator temperatureon performance of Vapour Jet Refrigeration (VJR) system.Furthermore, the effect of ejector efficiency also discussed atconstant operating conditions. The design conditions wereevaporator temperature (5-15 C), condenser temperature(30-45C) and generator temperature (75-80C). Forcalculation purpose mathematical equations are developed andsimulation results are obtained with EES (Engineering EquationSolver). The present results depicts that the performance of theejector highly depend on operating conditions on theperformance of ejector system.

Index TermsEjector, Mathematics, Performance,R134a, Refrigeration.

I. INTRODUCTIONRefrigeration and air conditioning is essential extensively

in world requirement of different applications like hotels,buildings, hospitals, manufacturing of ice, domesticrefrigerators, deep freezers, automobiles, heating andventilation. Refrigeration is a process of maintains of systemtemperature below than environment temperature byproviding continues supply of energy in form of electricity.Generally vapour compression refrigeration system (VCRS)is employed for meet refrigeration purposes in addition toabundant amount of electricity providing to mechanicalcompressor [1]. As we know to meet huge amount ofelectricity demand fossils fuels are used for energygeneration. By burning coal and fossils fuels we meet mainlytwo problems as follows:

One is emission of CO2 gas which is dangerous forenvironment. The other is increasing global warmingpotential due to emission of chlorine atom from refrigerants.

As a result, the European commission Regulation2037/2000, installed on 1 October 2000, a program to controlall the ozone depleting materials and all HCFCs (hydrochlorofluorocarbons) will be forbidden by 2015 [2]. One

Manuscript received February 20, 2015.Sonia Rani , School of Renewable Energy and Efficiency, National Instituteof Technology, Kurukshetra, India,Gulshan Sachdeva, Mechanical Engineering Department, National

Institute of Technology, Kurukshetra, India,

solution is to overcome this problem adoption of cleanenergy. However, we can use waste heat or solar heat forrefrigeration and air conditioning. For utilizing of solar heator waste heat Eejector air conditioning is attractive choice.Advantage of elimination of mechanical compressor nomoving part except pump makes it more reliable in addition toreduced maintenance cost. In the present study Munday andBagster theory is use according to which assumption of twodiscrete streams was considered [3]. The motive stream flowthrough primary nozzle and suction stream flow throughsecondary nozzle attains mixing of both fluids in mixingsection at constant pressure. Immediate mixing shock wavegenerate results to subsonic velocity of mixed stream whichcan be obtained by intersection of Fanno and Rayleigh linesproceeding through diffuser [4]. At outlet of diffuser mixedstream velocity is negligible.

In 1942, the constant pressure mixing theory of ejector wasdeveloped by Keenan and Neuman .They assumed constantpressure mixing ejector and many researchers used their studyfor further research work [5]. Sun and Eames described asimulation model for ejector refrigeration applications usingworking fluid as refrigerant R123 in place of R11. Theirresults showed that R123 is good alternative for R11 in airconditioning purposes. They also studied the effect ofvariable geometry on the performance of system at variableoperating conditions for optimum results [6]. Nehdi et al. [7]performed experiments on supersonic ejector and found resultfor optimum designing of ejector with Refrigerant R11.Diswas and wongwises experimentally investigated theperformance of ejector expansion refrigeration cycle withoutexpansion valve of evaporator and their results showedimprovement in coefficient of performance relative toconventional cycle [8]. Alexis predicted the maincross-section of ejector for refrigeration applications [9].Salvaraju and Mani developed computer program toinvestigate the effect of specific heat of working fluid andfriction on constant area mixing chamber [10].

II. EJECTOR PERFORMANCE AND MATHEMATICALMODELING

An ejector is a device which is used to entrain low pressurefluid by high pressure fluid without any mechanical powerinput. In fig.1 demonstrate the working of ejector system inwhich high pressure superheated vapour raised in generator(6). Now these vapours passes through ejector (2) in

Theoretical Performance Analysis of Vapour JetEjector for R 134a

Sonia Rani, Gulshan Sachdeva

Theoretical Performance Analysis of Vapour Jet Ejector for R 134a

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converging- diverging nozzle, entraining low pressure vapourrefrigerant into ejector from evaporator (1). The mixing oftwo streams is done in mixing chamber at constant pressure.After this mixed fluid passes through diffuser where pressureis recover at expense of enthalpy at stagnation condition ofvelocity at outlet. Fluid is come into condenser (3) to rejectheat with surrounding at constant temperature and pressure. Incondenser high pressure vapour refrigerant change into highpressure liquid refrigerant. After condensing it will divideinto two streams. One enters into evaporator via capillary tube(4) reducing pressure at constant enthalpy. Another one flowsinto generator (6) before passing through pump (5) to raisesthe pressure of liquid refrigerant.

Fig. 1: Schematic diagram of vapours jet ejector air conditioning

Fig. 2: Schematic diagram of ejector

A computer program is developed to calculate theperformance of system for range of parameters based on fourbasics equations.

a) Conservation of massb) Conservation of momentumc) Conservation of energyd) 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].

Fig. 3: Mollier chart of R134a

Momentum of fluid is assumed to be conserved at mixingsection. The mathematical equations which are used forcalculate the performance of ejector system as follows:

1 2 (1 )x x mV V V (1)Energy balance equation can be applied at mixing section

6 2 3(1 )h h h (2)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:

2 6 11 2( )aaV h h (3)Where 1ah is obtained from the equations:

6 6 6( , ) ( )as fas as gas fass s T P s s x s s (4)

( )as fas as gas fash h x h h (5)

6 1 6( ) / ( )n a ash h h h (6)By application of energy balance equation between 2 and

a2:2 2 22 2( )aaV h h (7)

(8)

2 2 2 2 2( )a fa a ga fah h x h h (9)Applied energy balance equation between section 3 and m:2 32( )mmV h h (10)Value of pressure Px is assumed lie between Pm and P3.

Similarly value of velocity at point Y can be calculated as:( )m fm m gm fmh h x h h (11)

( )m fm m gm fms s x s s (12)

( )ys m fys ys gys fyss s s x s s (13)( )ys fys ys gys fysh h x h h (14)

( ) / ( )my m ys m yh h h h (15)

(16)( )y fy y gy fyV V x V V (17)

International Journal of Engineering, Management & Sciences (IJEMS)ISSN-2348 3733, Volume-2, Issue-5, May 2015

49 www.alliedjournals.com

For constant cross-section area some assumptions are

taken 2400mA , Pd=Py and by intersection of Rayleigh and

Fanno lines Td can be calculated.

(18)

(19)( , )d d dh h P T (20)( , )d d dV V P T (21)

Where K1, K2 are constant and can be calculated byapplying same equation at y state.

At diffuser following equation are used:( , )d d ds T P (22)

3 3( )s d s ds s s T P (23)

3 3( , )s s dh T P (24)( ) / ( )my m ys m yh h h h (25)

3 3 3( , )h T P (26)By using above equation performance parameters can be

calculated.For VJR system coefficient of performance can be obtained

by using following equations:a) The fluid at exit of evaporator in saturated vapour

condition.b) The fluid at outlet of condenser in saturated liquid

condition.c) Fluid flowing through capillary tube is isenthalpic.d) The fluid at outlet of generator is in superheated

vapour condition.e) No heat losses in pipe.

Heat absorbed in evaporator:

2 1( )e eQ m h h (27)Heat supplied by generator,

6 5( )g gQ m h h (28)Work done by pump

5 3( )p gW m h h (29)COP of system is calculated as

2 5

6 4

( )( )

h hCOPh h

(30)

The Carnot COP of system is given by:( )( )( )( )

g c e

g c e

T T TCOPc

T T T

(31)

From the above equation performance of VJR is found andcompared with Carnot COP.

III. RESULTSThe performance of ejector is mainly depending on the

entrainment ratio. We have to calculate entrainment ratio bymathematical equation by iterative process which is highly

depend on condenser and evaporator temperature. By varyingthe operating conditions for ejector we study the variouseffects.

A. Effect of evaporator