Thermodynamic analysis of auto-cascade refrigeration cycles, with and without ejector, for ultra low temperature freezing using a mixture of refrigerants R600a and R1150
Thermodynamic analysis of auto-cascade refrigeration cycles, with and without ejector, for ultra low temperature freezing using a mixture of refrigerants R600a and R1150
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DOI：
10.1016/j.applthermaleng.2021.117598
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发表时间：
2021-10-22
影响因子：
6.4
通讯作者：
Manuel Salmeron-Lissen, Jose
中科院分区：
文献类型：
--
作者：
Angel Rodriguez-Jara, Enrique;Jose Sanchez-de-la-Flor, Francisco;Manuel Salmeron-Lissen, Jose
由于压缩比的限制，超低温应用所需的温度范围从-50摄氏度到-100摄氏度，单级系统不能经济地达到。不同类型的解决方案，如级联或两级系统，可以实现所需的工作条件。然而，这些系统通常是复杂的或过于昂贵的。解决办法可能是使用非共沸混合物的自动级联系统。本文提出了两个修改的自动级联系统，包括喷射器装置，以提高COP。第一种改进包括作为相分离器出口处的膨胀装置的喷射器，而第二种改进包括作为预压缩级的喷射器。碳氢化合物异丁烷（R600 a）和乙烯（R1150）的混合物被用作具有非常高的GWP的传统制冷剂的替代品。该研究首先评估了自由变量对每个循环操作条件的敏感性分析。评价的变量是压缩机压力排放，混合物的质量分数和相分离器温度。在喷射器增强循环的情况下，还包括喷射器效率和动力压力。然后，通过优化过程找到最佳操作条件。结果表明，喷射器作为膨胀装置的情况下，与0.45的乙烯的最佳质量分数的COP的12%的潜在改善。另一方面，引射器作为预压缩级与参考情况相比没有任何改进。本研究的结论是，乙烯和异丁烷的混合物是一个合适的组合自动级联循环，喷射器可以实施，以提高COP，而不会增加过多的复杂性和成本。
The temperatures required by ultra-low temperature applications, ranging from -50 degrees C to -100 degrees C, cannot be reached economically with single stage systems because of the limitation of the compression ratio. Different types of solutions such as cascade or two-stage systems could be implemented to achieve the desired working conditions. However, these systems are usually complex or too expensive. The solution might be found in the use of auto-cascade systems working with zeotropic mixtures. The present article proposes two modifications of the auto-cascade system by including an ejector device to improve the COP. The first modification includes the ejector as an expansion device at the outlet of the phase-separator, while the second includes the ejector as a precompression stage. A mixture of the hydrocarbons iso-butane (R600a) and ethylene (R1150) was used as an alternative to conventional refrigerants, which have a very high GWP. The study performed firstly assessed the sensitivity analysis of the free variables on the operating conditions of each cycle. The evaluated variables were the compressor pressure discharge, the mass fraction of the mixture and the phase separator temperature. In the case of the ejector enhanced cycles, the ejector efficiency and the motive pressure were additionally included. Then, the optimal operating conditions were found by means of an optimization process. The results showed a potential improvement in the COP of 12% for the case of the ejector as an expansion device, with an optimal mass fraction of 0.45 of ethylene. On the other hand, the ejector as a pre-compression stage did not show any improvement with regard to the reference case. The present study concludes that the mixture of ethylene and isobutane is a suitable combination for auto-cascade cycles and that the ejector can be implemented to improve the COP without adding excessive complexity and cost.