梯级多孔介质强化管壳式相变储热器性能研究

Study on the Performance of a Shell-and-Tube Latent-Heat Storage Unit Enhanced by Porous Medium With Graded Porosity

本文采用数值模拟方法,针对套管式相变储热器内填充两级多孔介质的熔化过程特性强化开展研究,多孔介质孔隙率沿载热流体流动方向变化。分析了梯级多孔介质的孔隙率分布和各级所占的体积对熔化速率的影响;提出了一种适用于动态相变过程的温度场均匀性因子,揭示相变过程的换热强化物理机制。研究结果显示,当保证多孔介质总质量一定时,载热流体入口段的孔隙率和体积应该大于后一段,以保证较短的完全熔化时间;且入口段体积存在最优值,最优体积随着该段孔隙率的增加而减小。

In this study, numerical method was used to study the performance enhancement of melting characteristic of a shell-and-tube latent-heat storage unit enhanced by porous medium with graded porosity. Porous medium with two-stage porosity was inserted into phase change material,and the porosity varied along the flow direction of heat transfer fluid(HTF). The effects of the rates of porosity and volume of the first stage(at the entrance of HTF) to those of the second stage on the melting rate were investigated. A new evaluation index named as uniformity factor of temperature filed was proposed to reveal the mechanism of heat transfer enhancement for the dynamic process of solid-liquid phase change system. The results show that, when the total mass of porous medium is fixed, the porosity and volume of the first stage should be larger than that of the second stage to ensure a shorter total melting time. However, a higher volume of the first stage does not always bring a shorter total melting time. That is to say, there exists an optimal volume of the first stage, and this optimal volume depends on the porosity. The optimal volume of the first stage decreases with the increase of the porosity of the first stage.