Transient Heat and Mass Transfer in Soils in the Vicinity of Heated Porous Pipes

This paper presents an analysis which describes the time dependent heat and mass transfer in soils. Local effective thermal conductivity as a function of soil material, moisture content and temperature were used from experimental data. Diffusion of liquid and vapor are both accounted for. Local thermodynamic equilibrium between liquid and vapor is assumed. Boundary conditions were chosen to represent a subsurface soil warming and irrigation system. Surface heat exchange was included as a function of varying atmospheric and surface conditions. The spacing and depth of the pipes were varied to find their effect on moisture and temperature distribution within the soil for both summer and winter environmental conditions. The result of expressing the governing equations in finite difference form and solving them numerically on a computer are presented in the form of temperature and moisture content distribution curves for summer and winter conditions. The results agree well with existing laboratory data. A steady-state closed form conduction solution with surface convection is also presented. Seasonal soil temperature variations are also presented for three climates for heated and unheated soils.