Analysis And Experimental Study On Rotary Expanders In Carbon Dioxide Transcritical Cycle

The development of the carbon dioxide expander, which is now the keytechnology of the refrigeration and heat pump research, is the subject of thedissertation. This study is on the purpose of designing a highly efficient carbondioxide expander. Employing an expander, the carbon dioxide transcritical cycle notonly have the advantage of environmental protection but also save energy. So thispaper presents both theoretical analysis and practical experience for its application. Comparisons of different measures such as using internal heat exchanger,improving compressor efficiency, increasing the coefficient of the heat transfers,adopting an expander and optimizing the cycle, show that the utilization of theexpander in the carbon dioxide transcritical system can improve the coefficient ofperformance of the system. The expansion process in the carbon dioxide transcriticalcycle is analyzed based on the irreversible thermodynamics. According to variousinlet parameters of the expansion process, the models of leakage, fluid flow and thespread velocity of the pressure wave are set up. On the basis of the theoreticalexpander model, the characteristics of the performance are analyzed. There exist theoptimal parameters to maximize the efficiency of the expander. The second generation expander with the redesigned blade is developed on thebasis of the former rolling piston expander and its theoretical analysis has been made.The expander with the new blade runs well with less irreversible loss and itstheoretical efficiency is higher compared with the former one. In addition, a swingexpander is developed and studied in the respect of kinetics and the irreversiblelosses. The results illustrate that there is quite a little leakage loss in this kind ofexpander and its theoretical efficiency is higher than that of the rolling pistonexpander with a new blade. By the means of the finite element method, the stressanalysis of the swing piston has been done. The results indicate that the maximumstress and the most grievous distortion take place at the base of the piston blade,however the extreme value is not that large, so it is quite fit for the swing piston toperform under high pressure disparity by choosing the optimal material andreasonable design. In this paper, the methods of the power recovery of the expander have beenwell discussed. The merits, demerits and feasibility of various types have beenpresented. The type of generating electricity is suitable for the system with large - III -capacity, and its output of the generator can drive some small equipments. Theexpander-compressor is favorable for the system with small capacity. Thearrangements of the expander-compressor in the system are studied. The researchshows that the coefficient of performance of the system can approach the optimumvalue when the expander-compressor supplies the second stage compression for thetwo-stage compression system. When the expander is connected to the maincompressor in the two-stage compression system, the coefficient of performance ofthe system can reach the highest point. The developed structure of theexpander-compressor and the design philosophy are presented in detail. Theinfluences of both the phase of two crank-shafts and the strength on the shaft on thefunction of the expander-compressor are analyzed. The experiments on the rolling piston expander with conventional blade, theredesigned rolling piston expander and the swing expander in the carbon dioxidetranscritical cycle have been conducted. Three prototypes can perform steadily. Thetest efficiency of the rolling piston expander with new blade is from 35% to 47%,while that of the swing expander is from 33% to 44%, they are higher than that ofthe rolling piston expander with a conventional blade. The experimental resultsdemonstrate that the design is effective in reducing leak...