Heat transfer characteristics of triple-tube latent heat storage system placed horizontally and vertically

Phase change heat storage technology can realize the utilization of thermal energy across time and space, which is of great significance for solving the problem of mismatch between supply and demand of renewable energy and promoting the energy structure adjustment of our country. However, the low thermal conductivity of phase change materials (PCM) severely limits the application and development of PCM technology. Compared with the traditional two-tube phase change heat storage system, the three-tube latent heat storage system (TTLHSS) has the advantages of large heat transfer area and good heat transfer uniformity. However, there is a lack of comparative research on the heat storage and release performance of the triple tube phase change heat storage system placed horizontally and vertically. Based on the above, this paper studies the heat transfer characteristics of the triple tube phase change heat storage system placed horizontally and vertically, and compares the influence of the tube length on the heat storage and release performance. The coagulation/melting model and Boussinesq model of Fluent software were used to calculate the coagulation and melting process of lauric acid with the same structural parameters placed horizontally and vertically. The results show that when the tube length is 250 mm, the solidification and melting time of lauric acid in the case of horizontal placement is less than that in the case of vertical placement, decreasing by 8 % and 45.9 %, respectively. In addition, it is found that the natural convection has little influence on the axial heat transfer, so the tube length has little influence on the horizontally placed TTLHSS, which can be simplified to a two-dimensional structure for calculation. Due to the phenomenon of temperature stratification in the heat storage process in the case of vertical placement, the heat storage performance will decrease significantly with the increase of tube length, so the tube length has a certain impact on the heat storage and release performance of the triple tube phase change heat storage system placed vertically.