Theoretical And Experimental Study On A Combined Power And Ejector Refrigeration Cycle For Low Temperature Heat Sources

Low temperature heat sources (<200?), such as solar energy, geothermal energy and low temperature waste heat, exist in the world extensively with different forms. Most of them can't be utilized by the conventional power machines efficiently, so larger capacity of low grade waste heat is rejected to the environment directly, which results in large-scale energy waste. Recently, low temperature heat sources have caught much attention of the world due to the contradiction between the blooming economic development and the energy requirement.Low-grade heat utilization technology has become the hot question in the energy saving research area. In recent years, many combined power and refrigeration cycles have been proposed to give effective solutions for low temperature heat sources. The proposed combined cycles can supply both power and refrigeration outputs simultaneously. According to the different principles of work, the proposed combined cycles can be classified into two categories including: (1) the combined power and absorption refrigeration cycle (2) the combined power and ejector refrigeration cycle. Each of the combined cycle has its own characteristic. Based on the low-grade heat utilization background, both theoretical and experimental research works are under investigated on the combined power and ejector refrigeration cycle. Main research contents are included as follow:(1) A combined power and refrigeration cycle is proposed for low temperature heat sources. The proposed cycle combines the Rankine cycle and the ejector refrigeration cycle using safe and friendly working fluids. The proposed cycle can convert the low-grade heat into power output and refrigeration output. A theoretical investigation was conducted on the combined power and ejector refrigeration based on the first and second law of thermodynamics. The characteristics of the combined cycle in power and refrigeration generating process were analyzed. Besides, the efficiency definition is discussed to evaluate the cycle performance properly.(2) The thermal model of the combined power and ejector refrigeration cycle is established based on scroll expander and ejector. The mathematic models of scroll expander and“constant-pressure mixing”ejector are discussed especially. Besides, the simulation program are developed using Matlab and Refprop softwares.(3) Based on the simulation model, parametric study is conducted to simulate the cycle performance. Some contents are analyzed including the effects of key cycle design parameters, key componets design parameters, heat sources parameters on cycle performance.(4)Based on the simulation model, working fluids selection of the combined power and ejector refrigeration cycle is discussed. Based on the solar thermal utilization background, 20 kinds of working fluid are analyzed and compared from several aspects including cycle efficiency, working pressre range, effects on key components, safety and environmental problem. Results show that working fluids with comparative higher critical temperature, such as R123, R600a, R245fa, are suitable for the proposed cycle.(5) A kW class experimental prototype is developed to validate the feasibility of the combined power and ejector refrigeration cycle. Experimental research is investigated using R600a as working fluids. The system performances are tesed under three different modes: power output mode, refrigeration output mode, power and refrigeration mode. The effects of heat source temperature, generating pressure, frequency of the convertor as well as loads on cycle performance are analyzed.(6) All research work was summarized and the future problems in the research process are discussed and the prospects of the combined power and refrigeration cycle for low temperature heat sources are presented.