Abstract:

Latent heat thermal energy storage technology is a promising option for future cost reduction in parabolic trough power system, however, low thermal conductivity of phase change material (PCM) is the major shortage leading to large temperature difference between heat transfer surface and solid-liquid interface of the PCM, and low energy storage rate. A charging experimental system was set up for testing the dynamic thermal behavior of phase change material in metal foam. Paraffin wax is used as PCM and its thermal properties were determined with differential scanning calorimetry (DSC). Metal foam was made of red copper. The sample of PCM-foam composite with semi-circular slot was placed inside a transparent cuboid Plexiglas enclosure, and a copper tube with the same radius as the semi-circular slot was in close bonding with the PCM-foam composite. High temperature water flowed through the copper tube as the heat transfer fluid (HTF) heating the composite material. The temperature field and melting process of PCM at pore size were studied using appropriate thermocouple and high definition camera. Thermal characteristics, including temperature profiles and position of solid/liquid interface were investigated and recorded, and the effects of heating temperature and flow rate of HTF on temperature uniformity and melting rate were documented and discussed. Metal foam could effectively improve heat transfer performance of PCM and decrease charging time Temperature difference was smaller and heating flux was larger in the composite than those in pure paraffin.

Key words: phase change, porous media, metal foam, natural convection, visualization

摘要：

相变材料的低热导率是限制潜热蓄热广泛应用的重要原因。将相变材料石蜡真空条件下注入到泡沫金属铜内制备泡沫金属铜-石蜡复合相变材料,通过铜的高热导率及高孔隙材料的大面体比来强化相变换热过程。采用DSC示差扫描量热法对石蜡进行热物性测量获得准确的石蜡相变温度及相变潜热。以管壳式相变蓄热结构为对象,提取对称结构进行可视化设计,对比纯石蜡及泡沫金属铜-石蜡复合材料在相同运行条件下的相变过程,追踪二者熔化过程的相界面位置随时间的演化过程并布置热电偶准确测量材料内部的温度分布。结果显示加入泡沫金属后的复合材料的内部温差明显减小,温度分布均匀,蓄热热通量显著增大,有效缩短相变时间并缓解了自然对流造成的顶部过热和底部不熔化现象。

关键词: 相变, 多孔介质, 泡沫金属, 自然对流, 可视化实验