Fundamental study on vane type compressor/expander combination for carbon dioxide

这项研究的目标是开发二氧化碳制冷系统中节流损失的回收技术，并改善循环性能。本文研制了叶片式膨胀机样机，并从实验和理论上对其性能进行了评价。理论研究表明，膨胀机的使用大大提高了循环性能，澄清了变工况时旁路和预膨胀造成的损失。研制的样机在2000rpm时的总效率为0.43，恢复了220W的功率，并成功地测量了跨临界膨胀过程。利用建立的跨临界膨胀过程的数学模型，对样机的性能进行了仔细的检验。各种效率和损失分析表明，转子端面泄漏和进气口压降是影响其性能的主要因素。因此，它确信，通过优化规格和应用密封装置，可以达到所需的性能。应用本研究开发的膨胀机，其性能改善幅度有望达到24%。此外，还开发了一种单转子压缩机/膨胀机机组，该机组有许多问题需要解决，但有望具有很大的潜力。由于制造精度不足以抵挡作用在转子上的径向载荷，尽管机组旋转，压缩机侧仍无法正常工作。今后将研制精密加工的单转子机组和已研制的双转子压缩机/膨胀机机组的运行。在阐明了这些压缩机/膨胀机机组对循环性能的改善及其特点的基础上，实现了CO_2制冷机组与压缩机/膨胀机机组的实用化。

The objectives of this study are development of recovery techniques for a throttling loss in a refrigeration system working with carbon dioxide and improvement of the cycle performance. In this study, a prototype of a vane type expander was developed and its performance was evaluated experimentally and theoretically. The theoretical study shows that the cycle performance is greatly improved by using the expander and the losses caused by bypass and pre-expansion at an off-design point are clarified. The total efficiency of the prototype expander developed in this study was 0.43 at 2000 rpm, the power of 220 W was recovered and the trans-critical expansion process was successfully measured. With using a mathematical model developed to analyze the trans-critical expansion process, the performance of the prototype machine was examined carefully. Each efficiency and loss analysis show that the leakage through a rotor face and the pressure drop at a inlet port are major factors decreasing the performance. It is convinced, therefore, that the required performance is achievable by optimization of the specifications and applying a seal device. The improvement of the performance is expected to be 24 % by applying the expander developed in this study. In addition, a single rotor type compressor/expander unit, which has many problems to solve but is expected to have high potential, was developed and tested. Since manufacturing accuracy was not enough against radial load acting on the rotor, the compressor side did not work well although the unit rotated. The single rotor type unit with the accurate machining will be developed and the operation of a compressor/expander unit of dual rotor type developed already will be done in future. With clarifying the performance improvement and characteristics of the cycle by using these compressor/expander units, we will achieve a practical use of CO_2 refrigeration unit with the compressor/expander units.