Improvement of domestic CO_2 air conditioner by integrating compressor/expander combination

为了通过恢复节流损失来提高二氧化碳制冷循环的能源效率，本文澄清了叶片式膨胀机和涡旋式膨胀机的基本性能，并对膨胀机中发生的跨临界泄漏流和膨胀机/压缩机组合循环的性能进行了研究。通过优化间隙和减少轴封，叶片膨胀机的总效率为59%。跨临界膨胀过程随膨胀机入口温度的变化而变化，虽然在入口温度较低时观察到闪速延迟，但在测试温度范围内获得了良好的性能。该涡旋式膨胀机采用涡旋式压缩元件，在不作较大改动的情况下，总效率可达56%，优化设计后仍有获得足够效率的潜力。采用通道模型对跨临界泄漏流进行了实验研究，采用考虑进口加速度、摩擦损失和泄漏间隙加速度损失的均匀流动模型对跨临界泄漏流进行了分析，但当泄漏变成阻塞流时，需要对模型进行改进。研制了压缩机/膨胀机组合机样机，并对其工作特性进行了测试。在考虑膨胀机和压缩机性能的情况下，对机组的运行平衡点和循环性能进行了考察。与带膨胀阀的循环相比，循环性能提高了21%。虽然在非设计条件下循环性能会下降，但通过旁路或预膨胀可以提高性能。在本研究中，尚未研制出性能优良的压缩机/膨胀机组合机。研究结果表明，CO_2空调系统是可行的。

As an attempt of increasing the energy efficiency of a refrigeration cycle working with carbon dioxide by recovering a throttling loss, basic performances of a vane type expander and a scroll type expander were clarified and trans-critical leakage flow occurring in the expander and performance of a cycle with an expander/compressor combination were examined in this study.The total efficiency of the vane expander is 59% by optimization of clearances and a reduction of a shaft seal. The trans-critical expansion process changes according to an inlet temperature of the expander, and although a delay of flash is observed when the inlet temperature is low, good performance is obtained over the range of tested temperature. The scroll expander which was made using a scroll compressor element without major modification shows the total efficiency of 56% and a potential of having enough efficiency with an optimized design. The trans-critical leakage flow was examined experimentally using a channel model and it can be analyzed by a homogenous flow model with taking account of inlet acceleration, frictional loss and acceleration loss in the leakage clearance although an improvement of the model is needed when the leakage becomes choked flow. In addition, a prototype of compressor/expander combined machine was developed and its operating characteristics were measured. Operating balance point and the performance of the cycle with the combined machine were examined with considering the performances of expander and compressor. An improvement of cycle performance is obtained by 21% compared to a cycle with an expansion valve. Although the cycle performance decreases under off-design conditions, the performance will be improved by a bypass or a pre-expansion. In this study, a superior compressor/expander combined machine was not developed yet. But achievements of this study show feasibility of a CO_2 air conditioning system.