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

作为通过回收节流损失来提高以二氧化碳工作的制冷循环的能量效率的尝试，介绍了滑片式膨胀机和涡旋式膨胀机的基本性能，研究了膨胀机跨临界泄漏流和膨胀机/压缩机组合循环的性能，滑片式膨胀机的总效率为59%通过优化间隙和减少轴密封。跨临界膨胀过程根据膨胀机的入口温度而变化，并且虽然当入口温度低时观察到闪蒸延迟，但是在测试温度范围内获得良好的性能。使用涡旋压缩机元件制造的涡旋膨胀机没有进行大的修改，显示出56%的总效率和具有优化设计的足够效率的潜力。采用通道模型对跨临界泄漏流进行了实验研究，考虑了进口加速度、摩擦损失和泄漏间隙加速度损失，可以采用均质流模型进行分析，但当泄漏变为阻流时，模型需要改进。此外，还研制了一台压缩机/膨胀机组合样机，并对其运行特性进行了测试。在考虑膨胀机和压缩机性能的情况下，分析了组合机循环的运行平衡点和性能。与具有膨胀阀的循环相比，循环性能提高了21%。虽然在非设计工况下循环性能有所下降，但通过旁路或预膨胀可以改善循环性能。在本研究中，尚未开发出一种上级压缩机/膨胀机组合机。但本文的研究成果表明了CO_2空调系统的可行性。

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.