Numerical Analysis for Transient Two-Dimensional Coupled Heat and Mass Transfer in Soils by Considering the Effect of Seasonal Frost

摘要

The aim of this paper is to provide a numerical solution for simultaneous heat and mass transfer within frozen soil surrounding building foundations. The soil freezing characteristic curve and therefore the ice content are obtained by combining a generalised form of the Clapeyron equation with the soil water retention curve (SWRC) and the thermodynamical equilibrium. The mass conservation is derived by considering the phase change and the water flux due to infiltration. Also, the heat conservation is derived considering phase change, conduction and convection of heat. This results in a system of coupled and highly non-linear differential equations. The numerical method used to solve the system of partial differential equations is based on a Galerkin finite element method with adaptive mesh refinement and dynamic time step control. The developed solution is validated by comparison with experimental data obtained from literature. An application is then presented to demonstrate the heat and mass transfer as a result of heat dissipation of a foundation. The distribution of temperature and ice water content are discussed and it is shown that in spring months (March, April and May), despite the temperature above 0°C at the ground surface, a frost zone still exists within the foundation soil. In the cold period, a high rate of heat transfer between the ground and the upper part of the basement wall causes a sudden change in temperature. Also, during the cold period, it is observed that the heat loss from basement walls is several times higher than the heat loss from the floor slab.