Several Thermophysical Problems Associated With The Thermal Energy Storage And Its Applications

The huge quantity of thermal energy is demanded for air-conditioning of buildings, hot water supply and drying processes. The supply of thermal energy can not fulfill such a demand, in terms of the mismatch both in time and intensity. In view of the efficiency of the energy utilization and energy-saving, a potential way is to use the heat pump with thermal energy storage.In this dissertation, several thermophysical problems related to the thermal energy storage and the water source heat pump (WSHP) are investigated. The contents consist of the modes of thermal energy storage and their efficiencies, the performance of WSHP and its applications, and the measurement and prediction of thermal properties of energy storage materials.Heat transfer problems associated with the latent heat storageThe hot probe method is investigated for measurement of the thermal conductivity of the phase change materials (PCMs), for the lack of the data of thermal properties. Two improvements are proposed. The first is to optimize the probe design, based on the theoretical analysis of the measurement principles; the second is to improve the precision of temperature measurement. The improved hot probe can conveniently be used for measuring the thermal conductivity of PCMs, both in liquid and solid states. From the experimental results, the relative measurement uncertainty is about 3%, and the measurement time is less than 20 seconds.Micro-encapsulated PCMs have been receiving much attention recently. Based the apparent heat capacity method for solving the Stefan problem, the heat charge and discharge of the encapsulated PCMs are investigated numerically. The results show that the micro-encapsulated PCMs characterize the desirable behaviors such as the heat transfer enhancement, the stable heat flow and high efficiency of heat exchange under small temperature difference. All these advantages mainly come from its scale characteristic.The process of the latent heat storage has been studied widely. However, few reports are addressed to the efficiency of the latent heat storage system. In this work, the system with internally flowing liquid is investigated. Combined the heat exchange effectiveness and utilization factor of the latent heat, the systematic efficiency is discussed. Although the scale characteristics of the system, the flow state of the fluid and the difference between the heat source and the storage temperatures are important for the system design, it is the key to enhance the heat transfer inside the PCM.Performance of WSHP and its applicationConsidering the demand of the energy-saving of buildings, a solar-aided heat pump system, in which a water tank is used for storage of the collected solar energy for the heat supply in the winter, is set up. The performance of the WSHP is experimentally investigated, with respect to various temperatures of the heat supply. As an additional application, the performance of the WSHP simultaneously served for air-conditioning and hot water supply is also experimentally investigated in the summer.A thermodynamic analysis is given to the WSHP for multi-functional applications. Compared with the energy consumption of two air-source heat pumps, served for refrigeration and...