Abstract:

Aiming at the problem of low heat transfer rate caused by the poor thermal conductivity of the phase change material, 3-D numerical simulation is used to study the enhancement effect of fins and porous media on the discharging performance of the cascaded latent heat storage system. Gradient porosity is proposed to further improve the discharging performance of the system, and different enhancement methods are analyzed and compared from the two aspects of the discharging rate and efficiency. The results show that adding fins has a more significant effect on heat transfer enhancement in the sensible heat discharging process, while adding porous media is more significant in the latent heat discharging process. Adding only porous media during the whole discharging process shows better thermal performance than adding only fins. When adding fins and porous media at the same time, the discharging performance of the system is the best, and the complete solidification time of PCMs is reduced by 40%. There is no significant difference in the discharging efficiency of the system under the three porosity gradient conditions, but in the case of negative gradient porosity, the discharging rate is higher and more uniform. Compared with the case of positive gradient porosity, negative gradient porosity has better thermal performance.

Key words: heat storage, phase change, heat transfer, thermodynamics, performance enhancement, gradient porosity

摘要：

针对于相变材料（PCM）导热性能差引起的梯级相变储热系统传热速率低的问题，利用三维数值仿真研究肋片和多孔介质对梯级相变储能系统放热性能的强化作用，在此基础上提出了梯度孔隙率进一步提升系统的放热性能，从PCM的放热速率和放热效率两个方面对梯级相变储能系统的不同强化方法进行了分析对比。结果表明肋片在显热放热阶段强化传热作用更显著，而多孔介质在潜热放热阶段强化传热更显著。整个放热过程只加入多孔介质比只加入肋片表现出更好的放热性能。同时添加肋片和多孔介质时，梯级相变系统放热性能最优，PCM完全凝固时间减少了40%。三种孔隙率梯度工况下，系统的放热效率无明显差异，但在负梯度孔隙率情况下，放热速率更高且更均匀。相比于正梯度孔隙率的情况，负梯度孔隙率具有更优的热性能。

关键词: 储热, 相变, 传热, 热力学, 性能强化, 梯度孔隙率