A Comparative Performance of Freon Ejector Refrigeration Systems

This paper presents the results of the analysis of an ejector refrigeration system operating with Freons as the working substance. Such a system is suitable for operating at subzero evaporator temperatures. The mass of motive refrigerant vaoour per hour per ton and the coefficient of performance are calculated for various assumed operating parameters such as boiler temperature, evaporator temoerature and condenser temperature with and without subcooling in the condenser. Using these results the performance data of the system is presented. It is found that use of higher boiling temperatures, lower condensing temperatures with some degree of subcooling and higher evaporator temperatures is beneficial. A criterion for comparing the performance with various working fluids is presented. Amongst R-11, R-12, R-21, R-22 and R-113 which are compared, R-21 is found to give best performance. A graphical method for selecting operating parameters for any of these refrigerants is suggested. INTRODUCTION Ejector refrigeration system with steam as the working medium is well known. However, it has the limitation of being inapplicable for refrigeration systems operating at below zero degree Celsius. Kalustian [ 1] examined the possibility of using Ammonia and reported it unsuitable due to higher pressure requirement in the system. Usage of Freons in ejector refrigeration system will have the advantage as it can provide refrigeration below 0°C and the need for vacuum in evaporator may be avoided. Besides, Freons have low boiling point and can be conveniently generated as motive fluid in the system utilising solar energy. Kumar and Charan [2] proposed such a system operated by solar energy and carried out the thermodynamic analysis of the cycle. They compared the coefficient of oerformance with Ammonia, Steam and Freon-11 as the working medium and reported Freon-11 as the best. A low value of mass of motive vapour (W) and high value of coefficient of performance (COP) is considered advantageous. Taking the case of R-11, Charan [3] showed that Wand COP depend upon various operating parameters and recommended use of highest possible boiler temperature, a lower condenser temperature with some degree of subcooling and the system to ooerate f)etter at higher evaporator temperature. In the present paper, the performance data of the system with various Freons such as R-11, R-12, R-21, R-22 and R-113 is presented and compared. THE SYSTEM ANO CYCLE ANALYSIS The schematic layout of solar energy operated ejector refrigeration system is given in Figure (1). Hot water from the heat storage tank circulates directly through a heat exchanger placed in the refrigerant boiler. The vapourised refrigerant attains high velocity in the nozzle and entrains the vapour from the evaporator. The combined vapours are then compressed in the diffuser section and discharged into the condenser where they are condensed. A portion of this liquid refrigerant goes to the boiler and remaining in the evaporator to maintain the mass balance. The evaporator is placed in a water tank where it chills the water for refrigeration purpose say for airconditioning in the layout shown. For other applications the evaporator may be kept in a brine tank. Figure (2) gives the temperature-entropy diagram of the thermodynamic cycle. The initial condition of the motive vapour at A is assumed to be dry and saturated for analysis purpose. The state of the motive vapour after accounting for the nozzle efficiency (eA8 J, entrainment efficiency (e8. 1 ) is at I. This mixes with the flashed vapour at K coming from the evaporator to reach the state c. The m1xture then gets compressed in the diffuser and after accounting for its