Performance of Latent Thermal Storage with Spherical Capsules Enclosed Phase Change Material

研究了空气基太阳能集热系统中相变蓄热的能量特性。对球形胶囊相变材料（PCM）的传热过程进行了实验研究，测量了不同空气流量下相变材料熔化和冻结过程的温度响应。在此基础上，建立了相变储热系统的准稳态传热模型、均匀温度模型和线性温度分布模型，为相变储热系统的长期性能评价选择合适的模型提供了理论依据。通过实验得到了不同流量下胶囊表面与环境空气之间的对流换热系数和相变贮箱两侧的压降。假设一个简单的空气为基础的太阳能加热系统与热泵，系统模拟进行，以研究长期的能量性能，在日本冬季天气条件下的五天。并与砾石、砖等其他显热蓄热材料进行了性能比较。研究了相变储槽容量对长期性能的影响，以及熔化温度、相变储槽形状、集热器面积和空气流量对长期性能的影响，以充分发挥相变储槽的优点。结果表明，相变蓄热材料的综合性能系数在较小的蓄热容量处有一个峰值，且峰值较尖锐。这意味着PCM储罐在储罐容量方面具有上级性能，但过大的储罐容量会导致性能低于其他材料。

Energy performance of phase change thermal storage in an air-based solar heating system was stueied. expeerimental study was conducted for investigation of heat transfer process in a spherical capsule enclosed phase change material(PCM), in which temperature response was measured for melting and freezing processes under various air flow rate. Then, three theoretical models, quasi-steady model, uniform temperature model and linear temperature distribution model, for heat transfer process in a spherical capsule enclosed PCM were developed to select an appropriate model for estimation of a long-term energy performance of a phase change thermal storage system. Convective heat transfer coefficient vetween capsule surface and ambient air and pressure drop across the PCM tank were obtained from experiments under various flow rate. Assuming a simple air-based solar heating system with heat pump, system simulation was carried out in order to study the long-term energy performance for five days under Japanese winter weather condition. And the performance of a phase change thermal storage was compared with other sensible thermal storage mateials as gravel and brick. The effect of PCM tank capacity on the long-term performance was studied as well as the effect of melting temperature, shape of PCM tank, collector area and air flow rate for the best use of PCM's merits. It was found tha the overall COP of thermal storage tank using PCM has a peak at smaller capacity than the other sensible thermal storage materials, and the peak is sharper. This means that PCM storage tank has a superior performance for tank capacity, but excessive tank capacity results in lower performance than the other materials.