Modeling of solidification including supercooling effects in a fin-tube heat exchanger based latent heat storage

摘要

Latent heat storages are a promising technology to increase both the efficiency of thermal energy systems and the penetration of renewable energy sources such as solar energy. A major challenge regarding latent storage technology is the relatively high costs resulting from expensive heat exchangers concepts required to transfer thermal energy from the storage material to the heat transfer fluid. Within the presented study, a new modeling method which allows for the optimization of complex heat exchanger designs such as fin-tube concepts in latent storages units is proposed. The mathematical model of the heat transfer in latent heat storages during the solidification process can account for the effects resulting from the supercooling of the phase change material. In order to achieve a low computational effort, the model is composed of two subparts. The first is a 3-dimensional model describing the thermal behavior of the phase change material surrounding the fin structure of the heat exchanger. The second is a 1-dimensional model of the tube coil which allows obtaining the overall heat flow rate in the entire storage unit based on the 3-dimensional phase change material model.The developed model is calibrated and validated using experimental data of a commercial sodium acetate trihydrate based storage unit of manufacturer Sunamp with a phase change temperature of 58 degrees C. A good agreement between experimental and simulated heat flow rates and heat transfer fluid outlet temperatures could be observed. Moreover, the model is capable of predicting supercooling effects with high accuracy. Due to the acceptable computational effort achieved, the developed model may be used for a heat exchanger geometry optimization in future studies.