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In this study, the theoretical design of a vapor ejector used in an air-conditioning system is performed and the designed ejector is then optimized via computational fluid dynamics. Based on the numerical simulations, two geometrical parameters, throat diameter and nozzle position, are optimized. Then, the effects of the operating parameters on the performance of the optimized ejector are investigated numerically. The optimized ejector geometry is used as a variable-geometry ejector by using a spindle in the primary throat and the performance of the system in various spindle positions is studied. The results show the importance of using a analytical design to obtain the overall geometry of the ejector and numerical simulation in order to achieve the optimal ejector performance. The variable-geometry ejector designed based on the proposed method in this study with using solar energy, in conjunction with a cold storage system, might be able to provide the necessary refrigeration for all day long.

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In this paper, numerical investigation was carried out for the sake of identifying optimum geometry for variable geometry ejector using in solar refrigeration system as the prerequisites to experimental tests. Variable geometry was made by using a movable primary nozzle and movable spindle in it. Vacuum tube collector was postulated as heat source and R600a used as working fluid. Condenser temperature based on Middle East area temperature and evaporator based on operative condition in HVAC system selected. Generator, condenser and evaporator operating temperatures have severe effects on the optimum geometry of ejector. Therefore, for maximum entrain ratio it is necessary to identify optimum geometry to cope with variations in operating condition. The results showed that using a variable geometry ejector is a requirement for cooling during the day. The following fluid structure was compared by entropy generation during mixing and shock phenomena. The results showed there is optimum back pressure to minimize fluid exit entropy. It coincides with critical back pressure. It was found that depending on back pressure maximum entropy generation happen by two reasons, mixing and shock phenomena.