Abstract:

Phase change heat storage technology plays an important role in using industrial waste heat and solar energy to solve the imbalance between supply and demand between heat energy and users. Due to the limitation of the physical properties of the phase change material, there are still problems such as low heat storage rate and uneven melting during heat storage and melting. In this paper, the effects of different parameters (number of fins, length, thickness, eccentricity and fin arrangement) of adding longitudinal fins on the heat storage performance of triplex-tube phase change heat storage unit were simulated by FLUENT software under the action of natural convection. The results showed that the heat exchange area was increased compared with the ordinary casing heat storage unit, and the time required for all the phase change materials to melt was shortened. Under the same number of fins, the length and thickness of the fins were the main factors affecting the heat storage unit and the average heat storage rate, when the fin length accounted for 50% of the radial length of the phase change material area, the melting speed of the heat storage unit was significantly accelerated and the heat storage and average heat storage rate were higher. Through the optimization design, it was found that the downward offset distance e of the inner tube had a significant effect on the melting process of the phase change material, and the heat storage unit with short eccentric distance took the least heat storage time, compared with the smooth tube heat storage unit, the melting rate of the phase change material was increased by 48.5%, and the heat storage time was extended if the offset distance was too long. Through the arrangement of the outer fins at the bottom of the infill heat storage unit, the melting process of the heat storage unit was accelerated to varying degrees, and the overall heat storage rate was improved compared with the original fin structure.

Key words: phase change heat storage, numerical simulation, enhanced heat exchange, heat transfer fins, latent heat storage unit

摘要：

相变蓄热技术在利用工业余热、太阳能等解决热能与用户之间的供需不平衡问题方面起着重要的作用，然而受相变材料自身物性的限制，蓄热熔化时仍存在蓄热速度低、熔化不均匀等问题。本文以三套管式相变蓄热单元为基本结构，利用FLUENT软件模拟研究了在考虑自然对流情况下添加纵向肋片的不同参数（肋片数量、长度、厚度、偏心距及肋片排布方式）对三套管式相变蓄热单元蓄热性能的影响。结果表明，三套管式蓄热单元内外双壁面共同加热，与普通套管式蓄热单元相比，换热面积增大，相变材料全部熔化需要的时间缩短；加装纵向直肋片的三套管蓄热单元的熔化速度进一步加快，相同数量肋片下，肋片的长度和厚度是影响蓄热单元蓄热量与平均蓄热速率的主要因素，肋片长度占相变材料区域径向长度的50%时，蓄热单元的熔化速度加快幅度明显且蓄热量与平均蓄热速率较高。通过优化设计，发现内管向下偏移距离e对相变材料的熔化过程作用显著，偏心距离较短时相变材料完全熔化所需时间最少，相比光滑管蓄热单元，相变材料的熔化速率提升了48.5%，偏移距离过长则会延长蓄热时间；通过加密蓄热单元底部外层肋片的排布，蓄热单元的熔化进程有不同程度的加快，总体蓄热速率较原肋片结构有所提高。

关键词: 相变蓄热, 数值模拟, 强化换热, 传热肋片, 潜热存储单元