Study On Heat And Moisture Transfer At High-Temperature In Wet Soil

Thermal energy storage in soil is an efficient and practical way for solar seasonal thermal storage, and has got the attention widely. Through the study of the phenomenon that coupled heat and moisture transfer on the thermal performance of soil under high temperature ground storage, not only perfected heat and moisture migration theory in the soil also guide the optimization of the design of solar seasonal thermal storage system. It is also a key that favor solar seasonal thermal storage system be widely applied. Theoretical and experimental methods were used to research the heat and moisture transfer in the soil.The experiments of charging heat (79℃or 59℃) and discharging heat (8℃) in unsaturated soil storage with different initial water content were done in a two-dimensional experimental setup. The effects of charging temperature and initial moisture content on the heat and moisture behaviors in unsaturated soil were analyzed. The temperature and moisture variation and the heat rejection or extraction abilities in various cases of heat source temperature and/or initial volumetric moisture content were analyzed.The results show that the charging and discharging behaviors in watery soil are drastically affected by temperature and initial moisture content. For soil with lower initial moisture content, the ability of thermal storage in the soil increases with the rejection temperature. On the other hand, the rejection temperature has nearly no influence on the soil storage ability when the initial moisture content is large enough. However, the rejection temperature always has influence on the heat extraction ability. Under the same rejection temperature, higher initial moisture content of the soil can result in higher heat rejection and extraction ability.A two-dimensional unsteady heat and moisture transfer numerical was built, which based on the mass and energy conservation. The numerical model was validated by comparing the results with experimental data, while some of the numerical simulations were carried out. Simulated results show that compared with the case of the thermal conductivity only, the heat and moisture transfer during high-temperature thermal storage has reduced the soil temperature, and the simulated results closer to the experimental value. And the results also prove the conclusion for the charging behaviors in watery soil are drastically affected by temperature and initial moisture content. Compared with the low-temperature thermal storage, the heat and moisture transfer has greater influence for the high-temperature thermal storage.