Most existing studies overlooked the impact of the working fluid charge on turbo-refrigerators for ultralow-temperature applications, especially not on the motor-driven turboexpander-compressor (MTEC) based turbo-refrigerators. This study addresses this gap by conducting an experimental study on a newly developed MTEC-based turbo-refrigerator prototype for ultralow-temperature freezing down to −120 °C. The prototype was tested at charge pressures ranging from 249.3 to 438.1 kPa and at different heat loads and at a maintained input power level. Test results indicate the effect of charge pressure on both compressor and expander efficiencies are negligible, whereas both the MTEC's additional efficiency and recuperator effectiveness exhibit a significant increase with increasing charge pressure. The increase in the recuperator effectiveness mitigates the decline in relative Carnot efficiency accounting for no additional losses with increasing charge pressure. Combined with the increased additional efficiency, this results in the net relative Carnot efficiency being only slightly affected by changes in charge pressure. Nevertheless, a slight peak net Carnot efficiency of 9.8 % corresponding to a test charge pressure of 294.6 kPa was noted for the presented prototype. When heat load levels are considered together, changing charge pressure has a greater effect on the relative Carnot efficiency at lower heat loads.

中文翻译：

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−120 °C 涡轮制冷机工作流体充注影响的实验研究


大多数现有研究都忽略了工作流体充注对超低温应用涡轮制冷机的影响，尤其是对基于电机驱动的涡轮膨胀压缩机 （MTEC） 的涡轮制冷机的影响。本研究通过对新开发的基于 MTEC 的涡轮制冷机原型进行实验研究来解决这一差距，该原型用于低至 -120 °C 的超低温冷冻。 该原型在 249.3 至 438.1 kPa 的充注压力范围内，在不同的热负荷下和保持输入功率水平下进行了测试。测试结果表明，增压压力对压缩机和膨胀机效率的影响可以忽略不计，而 MTEC 的额外效率和换热器效率都随着增压压力的增加而显着增加。换热器效率的提高缓解了相对 Carnot 效率的下降，因为随着装药压力的增加，没有额外的损失。结合增加的额外效率，这导致净相对卡诺效率仅受装药压力变化的轻微影响。尽管如此，对于所提出的原型，对应于 294.6 kPa 的测试装料压力，观察到 9.8% 的轻微峰值净 Carnot 效率。当同时考虑热负荷水平时，在较低热负荷下，变化的增压压力对相对卡诺效率的影响更大。