组合式相变材料最佳相变温度的热力学分析

采用组合式相变材料的蓄热系统较单一相变材料具有更为优越的传热和热力学性能,而相变温度对于蓄热系统性能具有重要的影响。为了使结果更具普适性,以热力学有效能分析为基础并忽略具体换热器形式和传热过程,推导了使用不同相变材料数时每种相变材料最佳相变温度的理论公式,并根据最佳相变温度计算了有效能利用率随着相变材料数的变化,结果表明当PCMs数增加到4种时,理论最大有效能利用率已达80%以上,比使用单一相变材料的理论最大有效能利用率高50%左右。以573.15 K热能蓄能为例,计算了使用1~4种相变材料时相应的最佳相变温度与最大有效能利用率,并以此为依据给出了实际最佳相变材料组合。

Thermodynamic analysis on optimum phase change temperature for multiple phase change materials

A thermal storage system using multiple phase change materials (PCMs)has much better heat transfer and thermodynamic properties than that using single PCM.The phase change temperatures of multiple PCMs have an important effect on the performance of the thermal storage system.To obtain generalized results,the analysis method for thermodynamic exergy is employed,with the type of heat exchanger and heat transfer process neglected.The theoretical equation for the optimum phase change temperature of each PCM is derived.The optimum exergy efficiency is calculated for different number of PCMs.The results indicate that the exergy efficiency could be up to 80% with 4 or more PCMs,which is about 50% higher than that using single PCM.With thermal energy at 573.15 K as example,the optimum temperatures and the maximum exergy efficiencies for one to four PCMs are calculated,and the optimum combination of multiple PCMs is given on the basis of theoretical results.