关键词: 相变, 多孔介质, 泡沫金属, 自然对流, 可视化实验

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