Investigation on the Anti-Freezing and the Heat Preservation Characteristics for a Semi-Underground Water Storage Tank

In cold regions, semi-underground water storage tanks (WSTs) have problems such as low water temperatures and local freezing during winter operation. For its anti-freezing and heat preservation, relevant theoretical analysis and technical exploration are urgently needed. The study employs numerical simulation to investigate the effects of different thermal insulation measures on the anti-freezing performance of WSTs. Firstly, the numerical models were established to analyze the temperature distribution characteristics of the water body under low-temperature ambient conditions. Secondly, an experimental platform was also constructed, and the numerical models were validated through experimental measurements. On this basis, a 1200 h transient numerical simulation was conducted for a large-scale semi-underground WST. Finally, comparative analyses were performed on temperature variations between the uninsulated and variably insulated cases, and insulation layers of varying thicknesses and materials. The results indicate that significant heat dissipation occurs through the top and sidewalls of the tank if there is no insulation, leading to a continuous decline in water temperature and a risk of localized freezing. As the insulation thickness increases, the internal temperature of the tank gradually rises. However, when the thickness reaches 150 mm, further increases yield only marginal improvements of thermal insulation performance. Further comparison between 150 mm rock wool and 150 mm polyurethane insulation shows that the polyurethane provides better temperature retention. Therefore, the addition of a 150 mm of thick polyurethane insulation layer is identified as the optimal scheme. Lastly, by combining numerical simulation with experimental methods, the studies established a dynamic temperature field analysis for semi-underground WSTs, which can provide a theoretical basis and technical guidance for the anti-freezing and thermal insulation design of WSTs in cold regions, and therefore promote the popularization and application of WSTs.