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

研究了空气基太阳能供热系统相变蓄热的能量性能。对球形胶囊封闭相变材料（PCM）的传热过程进行了实验研究，测量了不同空气流量下PCM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能量性能评估选择合适的模型。通过实验得到了不同流量下胶囊表面与周围空气的对流换热系数和PCM储罐的压降。以一个简单的空气热泵太阳能采暖系统为例，对该系统在日本冬季天气条件下5天的长期能源性能进行了系统仿真研究。并将相变储热材料与其他感热材料如碎石和砖的性能进行了比较。为了最大限度地发挥PCM的优点，研究了PCM储罐容量对长期性能的影响，以及熔化温度、PCM储罐形状、集热面积和空气流量等因素对PCM性能的影响。结果表明，采用PCM的储热罐的总COP比其他显热材料的储热罐在容量较小的情况下有峰值，且峰值更明显。这意味着PCM储罐在储罐容量方面具有优越的性能，但储罐容量过大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.