Thermal performance analysis of composite phase change materials for energy storage solar heat pump

Considering the different working modes and energy storage requirements of the energy storage solar heat pump system under solar radiation intensity of different seasons, this paper presents a kind of energy storage composite phase change materials with high and low phase change temperature, which can realize the seasonal maximum utilization of solar energy when filled in the collector of energy storage solar heat pump system. In summer, the solar radiation is strong in the daytime, the temperature inside the collector is high, and the composite phase change material in the collector can achieve relatively high phase change temperature and store energy. At night, the composite phase change material undergoes a solid-liquid phase change to release heat at a relatively high temperature. Since the temperature is high enough, the energy storage solar heat pump system uses this part of heat for heating water directly. Under winter conditions, the solar radiation is weak inthedaytime, the temperature inside the collector is low, and the composite phase change material in the collector stores heat at arelatively low phase change temperature. When releasingenergy at night, the composite phase change materials undergo a solid-liquid phase change to release heat at a relatively low temperature. Due to the insufficient temperature, the energy storage solar heat pump system uses this heat for producing hot water by operating the heat pump cycle. Therefore, it is necessary to prepare a kind of composite phase change material with two phase change temperatures for seasonal energy storage. According to previous research, two kinds of composite phase change materials 48#/62# paraffin and CA/62# paraffin were made up with 48# paraffin, 62# paraffin and capric acid (CA). The thermal performance of composite phase change materials for different ratios was studied, respectively. The phase change temperature, enthalpy and specific heat capacity of single phase change material and composite phase change material were determined by the American Diamond DSC thermal analyzer. The results indicated that in the processes of heating and cooling, the latent heat of phase change of 48# paraffin, 62# paraffin and capric acid (CA) were approximately equal, that was small under the cooling process. The DSC curve of CA/62 composite phase change material had two obvious solid-liquid phase change peaks. The latent heat and the temperature corresponding to the highest endothermic peak of composites phase change materials with different ratios all showed increasing trend with the increase of 62# paraffin ratio. Thermal storage performance experiments of the composite phase change materials with different compositions and ratios were conducted. The results indicated that the thermal storage process curves of the composite phase change materials were divided into three stages: Solid sensible thermal storage, phase change thermal storage and liquid sensible thermal storage. The phase change thermal storage process curve of the CA/62# paraffin composite phase change material was divided into two segments, which correspond to the solid-liquid phase change process of capric acid and the solid-liquid phase change process of 62# paraffin. Therefore, CA/62# paraffin composite phase change material can be used in energy storage solar heat pump system to achieve seasonal thermal storage. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.