Structural Optimization Study Of Pressure Exchanging Refrigerator

The core component of Pressure Exchanging Refrigerator (PER) is wave rotor, in which the low temperature gas is obtained by energy exchange between two fluids with shock wave and expansion wave. Compared with the traditional thermal machine, it has many advantages, such as small volume, simple fabrication, easy assembly and feasible for heat recovery. It can be used abroad in condition of requiring of large-capacity low temperatue gas, for example, Natural Gas Cryogenic Process, Ground experiment for aeronautics and astronautics.Isoentropic efficiency is the main performance index for refrigeration equipment with gas expansion, which is also the main index of PER. The study of performance optimization is done in three ways in this article, including the unsteady flow in wave rotor, numerical experiment and physics experiment.(1) Unsteady flow in wave rotor. Frist, the working process is devided into three parts, inclucing low temperature cycle, high temperature cycle and tube interior cycle. Second, the wave movement in wave rotor is analysed in detail with 1D theory of gas unsteady flow.Meanwhile, the principle of energy transformation and the flow field distribution during the working process are revealed. Finally, the wave pattern is ploted.(2) Numerical experiment. The 2D periodic simulation of the whole machine is done with the software of computational fluid dynamics—FLUNT by which the effect of flow field initialization in unsteady flow is eliminated.Then the overdetermined boundry condition problem due to model simplification are sloved through adding a heat exchang model between high temperature port and reflux port. Furthermore, some problems of the flow field are founded based on the simulation results, such as the high temperature zone in the tube interior cycle, the high speed of gas in outlet nozzle and the reverse shock wave in tube which are good guides for performance optimization(3) The study of optimizing the structure of inlet nozzle and outlet nozzle is conducted with simulation and experiment. With the improved structure, Problems which have been discovered in 2D periodic simulation of the whole machine are sloved, and the isoentropic efficiency is increased largly.(4) Influence of different operating parameters on performance is studied by experiment Operating parameters are chosen based on experiment process, including expansion ratio, different inlet and outlet pressure in the same expansion ratio, the angle between inlet and outlet nozzle, temperature of reflux port and temperature of high pressure port.The study on optimizing flow field in PER has been done by simulation and experiment. The results reveal: the mass of gas in tube interior recycle is reduced by increasing the width of inlet nozzle, which can increase the isoentropic efficiency signifinately; the reverse shock wave can be eliminated by the structure of wave attenuator; the influence of revease flow port temperature on isoentropic efficiency is little, so water cooling can be adopted to reduce operation cost. The isoentropic efficiency has been increased 6～9 percent by optimizing the performance of PER and is stable at 64 percent with a maximum value of 67 percent.