Simulation And Experimental Research On CO₂ Two-cylinder Rolling Piston Expander

Ozone depletion and global warming could cause serious environmental problem. Natural refrigerant CO₂ enters into our horizon again owing to its benign and environmental behavior. The application of expander is the key point to improve the efficiency of CO₂ refrigeration system undoubtedly. This paper simulates the work process of CO₂ two-cylinder rolling piston expander by software Fluent and Fortran, and the simulation results of intermediate channel with different length and diameter display the optimal size of the channel. The expander is improved after this simulation. And the experiment is carried out in order to test its performance.The working process of the expander was analyzed firstly in this paper. The structure of the expander and calculate method of its working volume were also introduced following. The efficiency of the preceding prototype was not very perfect. The improved measures aiming to increase efficiency of the prototype were summarized and a new scheme of the intermediate channel owing to optimizing the expansion ratio was put forward in this paper.The process including flow, pressure releasing, leakage, friction losses were simulated and certain conclusions were arrived in the view of intermediate channel with different length and diameter by the software Fluent and Fortran. The pressure analysis results were consistent with the two simulation methods. Results of one method can become the supplement of the other one. And the research and design of the expander can be directed by the two methodsThe CO₂ trans-critical water-water heat pump system was given a minute description, and the research content, purpose and methods were formulated in the paper. The experiment of the modified expander was carried out on the heat pump system aiming to complete the efficiency test. The intermediate channel of the expander was modified in the first phrase, which should decrease the length and diameter at the same time. The best working condition is about 26℃,6.5MPa in the experiment processes, the highest recover power is up to 200W, and the maximum efficiency reaches approximately 42.3%. The expansion ratio of the expander is arrived at 2.2 or so, which is closed to the theoretical ratio 2.5. But the leakage problem still exists and the first-stage of the expander can be reduced further, the efficiency of the expander would raise more if the problem is solved and the measure is effective applied. In a word, there still exists further improvement room of this prototype.