| The gas wave mechanery (GWR) is a kind of expansion refrigeration equipment that uses the movement of the pressure waves in oscillation tube to separate cold and hot. Compared with the turbine expansion refrigeration, it has advantages as simple structure, low rotation speed and can work with liquid, etc.To research the characteristics of waves in oscillation tube, we can enrich and perfect the theory of wave machines. In additional, it has theoretical and practical values for promoting the engineering application of GWR.The expansion work of high pressure gas in traditional GWR is dissipationed just as heat. In other words, this is quite a waste of energy. This paper based on the idea of gas wave supercharging and proposed a method of novel over expansion gas wave refrigeration (OEGWR), in order to enhance the performance of traditional GWR. The OEGWR use the shock wave in oscillation tube to compress the low pressure gas form the expansion of high pressure gas. In this way, the expansion work of the high pressure gas can be recycled in the form of pressure energy. It will lead to the actual expanssion pressure ratio (Pressure ratio of before and after the expansion of high pressure gas) greater than the pressure ratio of system (The ratio of the system of import and export pressure). Thus, the refrigeration temperature drop under small pressure ratio can be improved greatly.When the gas is wet, the phenomenon of condensation will appeared during the unsteady expansion process of high pressure gas in oscillation tube. Under coupling and interaction of condensation latent heat and unsteady flow field, it will affect the refrigeration wave diagram in oscillation tube. Especially when the quantity of condensation latent heat released reaches the condition of thermal choking, the strong condensation shock can be produced in oscillating tube and the port matching of GWR will deviated from the theoretical design. Based on the classical nucleation theory, a numerical model of unsteady condensing flow was established in this article. The condensation phenomenon of moist air in shock tube which caused by the expansion wave was studied, and theoretical and numerical analysis the choking phenomenon caused by condensation. Finally, the wave diagram has been investigated under different initial moisture content, which is influenced by the condense process in oscillation tube.In this paper, the main work and conclusions are as follows:(1) Based on the system analysis of the formation and fluctuation characteristics of pressure waves in oscillation tube, the ideal refrigeration wave process was built and has been developed a refrigeration system of OEGWR. Under the experimental pressure ration of system (the ratio of1.1～1.5),1.7times of the expansion degree is available, and can recycle about40%of the pressure energy.(2) To simplify the complex wave process in oscillation tube as two shock waves and three expansion waves, based on the one-dimensional unsteady flow theory, the quantitative matching relations of waves in oscillation tube was established for rapid predicting the port arrangement of OEGWR. According to that, the theory design basis of port matching was laid. Additionally, the relationships of shock pressurize characteristics with the channel open time τ and expansion ratio was analyzed. Results show that the supercharging efficiency of shock wave in oscillation tube increases with the decrease of the turn on time τ, while decreases with the increase of expansion ratio.(3) Consider the change of gas mass flow rate before and after of condensation area, an explicit equation for the critical quantity of condensation heat flow has been derived. It can theoretically predict the critical quantity heat of chocking flow and the results show that the decrease of mass flow rate before and after the zone of condensation will make the critical heat increased. Theory proved that the propagation speed of condensation shock is faster than the movement speed of condensation zone, in conformity with the literature phenomenon of experimental observation.(4) Based on the unsteady condensing flow numerical model is established, the phenomenon of unsteady condensation flow in oscillation tube was studied. The regular of the condensation heat effect to the wave process in oscillation tube is revealed. The release of condensation latent heat can cause the moving velocity of shock wave increases, and the calculation shows that, the shock wave movement speed will increased by5%with gas moisture content was0.44%. In the wave rotor port matching design, should consider to condense effects on the wave process in oscillation tube.(5) Based on the research of energy transfer process and thermal separation principle of OEGWR system, the thermal analysis model of OEGWR had been established. The performance of system under the condition of diffident operating parameters was analyzed. Results show that after introducing pressurization process to recycle the expansion work of high pressure gas, the pressure ratio of refrigeration system can be greatly reduced. The refrigeration efficiency of OEGWR system decreased with increasing of refrigeration pressure ratio. When the refrigeration pressure ratio of system is greater than3.0, the changing of refrigeration efficiency with pressure ratio will become stable. Compared with the compression process of system, improve the efficiency of expansion process of system will make more conducive to improve the efficiency of the refrigeration system. When the outer loop flow of low temperature gas equals to the system, the refrigeration efficiency of system will achieve maximum.(6) According to the industrial standard, an experimental platform of OEGWR was established. The refrigeration performance of OEGWR was studied under the condition of different structural parameters and operating parameters. The experimental results show that the temperature drop of OEGWR system will up to26℃～38℃with pressure ratio of1.1～1.5. It is significantly higher than that of traditional GWR and verified the effectiveness of the method proposed. The influences of some parameters, including refrigeration pressure ratio, port size and offset, outside circulation flow of low temperature gas, on the performance of OEGWR are investigated, and the influence mechanisms are analyzed. Furthermore, the operation law of OEGWR is found, and its industrial application is guaranteed. |
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