Direct Solar Thermal Energy Storage Using a Semitransparent Phase Change Material

提出了一种新型的被动式太阳能储热系统--体积热阱（VHT）型潜热储热器，该系统利用太阳能直接加热并熔化相变材料（PCM）的平面层。通过室内和室外实验研究了其性能，并进行了理论分析。对表面热阱（SHT）型潜热蓄热和VHT型感热蓄热进行了平行试验。以石蜡为相变材料，测量了集热器内温度分布随时间的变化。改变收集器的倾斜角度和PCM的厚度。在理论分析中，假设二维流动和传热，并应用总比热的概念，推导出基本方程，并进行数值求解。讨论了倾斜角度和相变材料厚度对温度分布和蓄热效率随时间变化的影响。结果表明：1）计算结果较好地反映了实验数据的变化趋势，说明本文的理论分析是正确的; 2）VHT型潜热蓄热上级SHT型潜热蓄热和VHT型显热蓄热; 3）在VHT型潜热蓄热中，在室外实验中，最适宜的倾斜角度是太阳入射角，太阳入射角的大小对太阳能电池的储热特性有一定的影响。

The latent heat storage of a volume heat trap (VHT) type was proposed as a new passive system of solar thermal energy storage, in which a plane layer of a semitransparent phase change material (PCM) is directly heated and melted by the sun. The performance was investigated in the indoor and the outdoor experiments and analyzed theoretically. Those of the latent heat storage of surface heat trap (SHT) type and the sensible heat storage of VHT type were examined in parallel. Paraffin wax was used as a PCM and the time changes of temperature distributions in the collector during heat storage weremeasured. The tilt angle of the collector and the thickness of PCM were varied. In the theoretical analysis, the basic equations were derived by assuming the two-dimensional fluid flow and heat transfer and by applying the concept of overall specific heat, and were solved numerically. The effects of the tilt angle and the thickness of PCM on the time changes of temperature distribution and heat storage efficiency were discussed. As a result, the following conclusions were obtained.1) The calculated results reasonably expressed the tendencies of the experimental data so that the present theoretical analysis was considered to be valid.2) The latent heat storage of VHT type was superior in performance to the latent heat storage of SHT type and the sensible heat storage of VHT type.3) In the latent heat storage of VHT type, the internal heating and the heat and fluid flow by natural convection affected the characteristics of heat storage.4) In the outdoor experiments, the most suitable tilt angle was found to be solar incidence angle at the time of culmination.