过冷度对制冷循环性能影响的理论分析与实验研究

发布时间：2018-01-26 10:20

  本文关键词： 过冷 单级蒸气压缩式制冷循环 性能系数 数值计算 实验研究　出处：《华北电力大学》2014年硕士论文　论文类型：学位论文

【摘要】：随着城镇化进程加速和居民生活水平的提高，空调系统的能源消耗占我国总能耗的比重也日益增加。提高空调系统的能效水平对于节能减排和实现可持续发展具有重要意义。液体过冷总是可以提高空调系统的性能系数，已经被广泛采用。因此本文结合空调系统的工质替代和经常部分负荷运行的特点，采用理论分析和实验研究相结合的方法，研究如何运用过冷提高空调系统的循环性能。 以单级蒸气压缩式制冷循环为对象，根据GB/T18430.2-2008标准，采用EES软件编程计算。对于R134a工质，随着冷凝温度、高压压力的升高以及蒸发温度的降低，单位过冷度引起的系统性能系数COP的增大值减小。而对于常用的制冷剂，虽然过冷总是提高循环的性能，但单位过冷度对不同制冷剂COP的提高不一致，，如对R218和R125增幅较大，而对R717和R407C提高较小。 在R134a单级蒸气压缩式制冷实验台进行了实验，验证在过冷条件下，冷凝温度和蒸发温度的变化对循环性能的影响。实验和理论分析都表明：蒸发温度变化所产生的单位过冷度的COP值变化要大于冷凝温度。 对于单级蒸气压缩式制冷循环，合理设计冷凝器，可获得过冷。通过建模和计算分析，对于R134a工质，每增加1℃过冷度，冷凝器的换热面积需增加6.5%。所以权衡系统的性能和经济性，过冷度需控制在一定的合理范围内。 采用独立机械式过冷循环、喷射式过冷循环、回热过冷循环和蓄冷式过冷循环也可以达到过冷效果。如对于独立机械式过冷循环，5℃的过冷使COP提高约16%，并使最佳中间温度明显降低。喷射式过冷循环也提高了系统的制冷效果，但是当过冷度达到某一温度时，循环的性能系数存在一个最大值。回热过冷与制冷剂的热物理性质有关，对于回热过冷有利的制冷剂，回热过冷度越大，单位质量制冷量和COP增加百分比越大。对于蓄冷式过冷循环，冷量增量和增加率都随过冷度的增加而增加。
[Abstract]:With the acceleration of urbanization and the improvement of living standards. The energy consumption of air conditioning system is increasing in our country. Improving the energy efficiency level of air conditioning system is very important for energy saving and sustainable development. Liquid undercooling can always improve air conditioning system. The performance coefficient of. It has been widely used. Therefore, this paper combines the characteristics of refrigerant substitution and regular partial load operation of air conditioning system, and adopts the method of combining theoretical analysis with experimental research. How to improve the circulation performance of air conditioning system by undercooling is studied. The single stage vapor compression refrigeration cycle is taken as the object. According to GB/T18430.2-2008 standard, the calculation is carried out by EES software. For R134a refrigerant, the condensing temperature is increased. With the increase of high pressure and the decrease of evaporation temperature, the increase of system performance coefficient (COP) caused by unit undercooling decreases, while for common refrigerants, the performance of cycle is always improved by undercooling. However, the increase of unit undercooling degree is not consistent with that of different refrigerants, such as R218 and R125, but slightly for R717 and R407C. The experiment was carried out on the R134a single stage vapor compression refrigeration test rig, and it was verified under the condition of supercooling. Experimental and theoretical analysis show that the COP value of unit undercooling caused by the change of evaporation temperature is greater than that of condensation temperature. For the single stage steam compression refrigeration cycle, the supercooling can be obtained by reasonably designing the condenser. Through modeling and calculation, the supercooling of R134a working fluid is increased by 1 鈩

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