This thesis describes the performance of an ejector cooling system and the effect of the ejector geometry. In the present study, ammonia is selected as working fluid as it has good properties in comparison with the other refrigerants. For this thesis, a two-dimensional axisymmetric ejector model is chosen and continuity, momentum and energy equations are solved by numerical method with Fluent software and result are shown to be in good agreement with previous analytic work and it is validated. Thermodynamic cycle analysis done with EES software to calculated the heat of generator (Qg), heat of evaporator (Qe), work of pump (Wp) and coefficient of performance (COP). Results show that the entrainment ratio and the outlet ejector temperature increase with the increase of generator temperature, in evaporator and condenser constant temperature; also it increase the Qg, Wp, Qe and COP. The entrainment ratio increase and the outlet ejector temperature decrease with the increase of evaporator temperature, in generator and condenser constant temperature; also it increase the Qe, but Wp and Qg remain constant, so the COP increase. When ejector works in critical mode, the condenser temperature doesn't effect on entrainment ratio. After analysis of flow in the ejector, the geometric parameters for design a high performance are investigated. We used 157 ejector with different geometry. The result shown that the diameter and length of mixing chamber has the most and diffuser angle has the least effect on ejector performance. Also the optimum values have relationship with the diameter of mixing chamber and it can show them in the form of dimensionless. This optimization can improve ejector performance by up to %16. Then the effect of generator and evaporator temperature on ejector performance are investigated. The results show that the best performance of the ejector is achieved in greater lengths with increasing of generator and evaporator temperature. Also the best performance of the ejector is obtained with increasing generator and evaporator pressure in bigger distance from nozzle to mixing chamber. The results show generator and evaporator temperature doesn't affect the optimum values for the length and angle of diffuser. Keyword: ejector, ejector refrigeration cycle, geometry optimization
