Simulation, design and analysis of a novel latent heat storage system for thermal storage of electric power

Abstract

The consumption of electricity has to be matched with the generation in all grids in order to maintain a safe and stable electricity supply. The over-produced electricity must be stored or wasted to maintain the balance. Batteries are generally too expensive for storing large amount of electrical energy. Therefore, converting electrical energy into a more storable form of energy is another option for large scale storage. In this thesis, a latent heat storage system is designed to store electrical energy in the form of thermal energy. The storage material changes its phase as energy is charged or discharged into the system and a large amount of latent internal energy can be absorbed or released through the phase change. However, the capacity of the storage system is limited by the relatively low thermal conductivity of the phase change material (PCM). This thesis focuses on improving the heat transfer efficiency during charging and discharging. For this purpose, the conceptualized thermal energy storage system is simplified to a 2D model and a eutectic mixture of potassium nitrate and sodium nitrate is used as the storage material for the model. The engineering simulation software ANSYSTM is used to simulate the melting and solidification process of the PCM in the storage chamber. Due to the low thermal conductivity of the PCM and the small contact area between heaters and PCM, heat transfer structures (HTSs) have been introduced into the model to increase the contact area between the PCM and the heaters. Seven different HTSs are simulated in the 2D model to compare the improved heat transfer efficiency for both charging and discharging. In addition to the HTS, the aluminum tube wrapped outside the cartridge heater redistributes the heat flow from the heaters, which also shortens the charging time. Another option to improve the heat transfer efficiency is increasing the power level of the heater. Three different power level heaters (0.8 W, 1.0 W, and 1.2 W) were used to simulate the 2D model with seven HTSs to observe different behaviors of the PCM in the storage chamber. These results serve as a guide for building a prototype of this latent heat storage system in the future.