最小热阻原理在组合式相变材料蓄热过程优化中的应用

Application of minimum thermal resistance principle in optimization for melting process with multiple PCMs

最小热阻原理为近年来火积理论中所提出的传热过程优化的新方法.本文基于最小热阻原理对组合式相变材料蓄热过程进行了优化.通过变分原理,获得了组合式相变材料最佳融化温度的通用表达式.在此基础上,进一步研究了相变材料数对火积耗散热阻和蓄热性能的影响,探讨了最小热阻原理用于组合式相变材料蓄热过程优化的可行性.定义了组合效率,考察了传热单元数和热容流率对火积耗散热阻的影响.结果表明,组合效率随相变材料数的增加逐渐提高,火积耗散热阻随传热单元数和热容流率的增加逐渐降低其提高与降低的幅度均逐渐减弱,该研究为组合式相变材料的遴选以及流动和结构参数的设计提供了理论指导.此外,基于最小热阻原理的优化分析,提出了相变蓄热过程的温差场均匀性原则,为组合式相变材料的优化提供了一种新的优化标准.

The minimum thermal resistance principle has been developed in recent years,which represents a new method for optimization of heat transfer processes. In this paper,the minimum thermal resistance principle is further developed for optimization of melting process with multiple phase change materials（PCMs）. The general formulas of the optimum melting temperature are deduced on the principle of calculus variation,subject to different optimization objectives. Base on the general formulas,the effects of numbers of PCMs on entransy dissipation-based thermal resistance and thermal performance are discussed. The more PCMs used in melting process can reduce the entransy dissipation-based thermal resistance to improve the thermal performance. The results show that the minimum thermal resistance is suitable for melting process optimization with multiple PCMs. Moreover,the combinational efficiency is defined to estimate the thermal performance for multiple PCMs conveniently. The effects of the number of heat transfer unit and heat capacity flowrate on entransy dissipation-based thermal resistance are investigated. The results indicate that,the combinational efficiency can be increased with increasing of numbers of PCMs,and the entransy dissipation-based thermal resistance can be decreased with increasing of the number of heat transfer unit and heat capacity flowrate,and both of the effects are gradually weakened. Thus,a theoretical guidance is provided for selecting the multiple PCMs and designing flow and structure parameters. In addition,based on the minimum thermal resistance principle,the uniformity principle of temperature difference field is proposed as a new optimization criterion for melting process with multiple PCMs.