Abstract: The feasibility of sand at various grain sizes as filler material for solar sensible heat thermal energy storage (TES) was investigated. An indirect contact sensible heat TES experiment setup was built. The TES section is a cylindrical tank, which is embedded with 19 stainless tubes arranged like a hexagonal honeycomb. Air was chosen as the heat transfer fluid to flow inside the tubes and carry heat, while the sand in the tank contacts the outside of tubes. Four types of sand: silver sand, medium sand, filter sand and coarse sand, were selected. The results show that voidage is the determining factor for the TES performance rather than density or grain size. Coarse sand is the best among the four types. For materials such as sand whose basic thermal properties only vary a bit, the change of charge temperature can hardly affect the TES performance. When using air as the heat transfer fluid, the TES efficiency is relatively lower. To enhance heat transfer, a lower air velocity or longer tube length is needed. The simplified 2-D simulation results match well with the experimental results and can be used for the prediction of large scale TES tank performance.

Key words: sand, solar energy, thermal energy storage, filler material, voidage, heat transfer

摘要： 建立了间接接触式显热蓄热实验台,对不同粒径的砂砾用于太阳能显热蓄热斜温层单罐填料的蓄热特性进行了研究.实验台蓄热装置为一圆柱形罐体,内部按六边形蜂窝状布置了19根不锈钢管.选用空气作为换热流体,流经钢管内部通道传热,钢管外部用于与罐体内的砂砾相接触.选取了4种砂砾:细砂、中砂、滤砂和粗砂进行实验.结果表明,空隙率是影响砂砾蓄热性能的重要因素,而不是密度或粒径.其中,粗砂空隙率最低,蓄热效果最好.对于砂砾等基本物性变化不大的材料,不同蓄热温差下,蓄热效果相同.采用空气作为换热流体,蓄热效率较低,需要降低空气流速或者加长管段以强化换热.实验结果与二维简化数值模型进行对比,结果吻合良好,该模型可用于进行大型蓄热罐蓄热性能研究.

关键词: 砂砾, 太阳能, 蓄热, 填料, 空隙率, 传热