Performance Analysis Of Knudsen Compressor And Refrigeration Systems With The Knudsen Compressors

A Knudsen compressor, based on the principle of the micro/nano-scale thermal transpiration, is a micro-scale apparatus. It is typically composed of a series of micro-channels and a connector, has a simple structure without moving part, and can utilize the low-grade heat energy. Applied it into refrigerant system, it could be a new way to solve energy and environment in refrigerant field.Firstly, in this thesis, assuming thermal transpiration happened in microchannel and connector of Knudsen compressor, the flow and pressure model of single-stage Knudsen compressor has been established. Based on above models, the best flow state in microchannel and connector, the influence of structure sizes and operating conditions on its performance of Knudsen compressor have been discussed and analyzed. As a result, Knudsen compressor performance reaches the best condition when the flow in microchannel is in a free molecular flow states (that is, Knudsen number equals 10); the closer the flow in connector is to continuous flow state, the better performance of Knudsen compressor is; Knudsen compressor efficiency achieves the max-value when the flow is in the transition flow (Knudsen number equaling to 0.695). Knudsen compressor performance is proportional to the radius of microchannel and connector and is inversely proportional to their length. The lower operating conditions of Knudsen compressor is, the better the performance is, and the more significant the influence of factors is.Secondly, based on the single stage Knudsen compressor results, the performance model of multi-stages Knudsen compressor has been established. Then the influence of pressure difference coefficient, series stages, and structure parameters on Knudsen compressor performance have also been discussed. The study shows that the influence of these factors on multi-stages Knudsen compressor is similar to the single stage Knudsen compressor, just the more series it has, the more notable it is.Besides, combined above results with the working condition of air conditioning, several refrigeration systems with the Knudsen compressors, which employed ammonia, water, R290 and R600a as working fluids, have been designed, and performance of these system have been analyzed respectively. At last, the most optimal refrigerant system with Knudsen compressor water system, using water as working fluids, has carried on the further simulation analysis. The operating characteristics of the proposed refrigeration systems are similar to those of conventional vapor compression refrigeration systems with variable speed compressors, that is, the COPs increase with indoor temperature raise or ambient temperature drop while the cooling capacities decrease at the same conditions.