Ejector refrigeration cycle could provide cooling by using thermal energy with drastically small consumption of electricity. Furthermore, this system could make an effective use of lower-temperature energy resources such as solar thermal energy or exhaust heat at lower temperature than 100°C. The ejector design is responsible to the cycle efficiency. Therefore, in this research, CFD analysis is conducted to improve the efficiency by the ejector configuration design. As a consequence, notable two configuration parameters were obtained: mixing section area A_(MIX), and nozzle exit area A_(ne). The efficiency at critical mode improves with an increase of the mixing section area A_(mix), although the critical condensing pressure drops down. In other words, the optimal mixing section area A_(MIx) varies with the condensing pressure. Meanwhile, optimization of expansion mode, which is designed by the nozzle exit area A_(NE), improves both the efficiency and the critical condensing pressure. Expansion mode should be correct expansion to minimize total pressure loss. Since pressure gradient in the suction chamber is nearly zero, correct expansion could be simply defined as the case that nozzle exit pressure equal to evaporating pressure.
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