Soil thermal diffusivity and water transport in unsaturated, nonisothermal, salty soil

Abstract

<p>Soil apparent thermal diffusivity was determined from field temperature observations using the first harmonic and multi-harmonic temperature analyses. Water transport was studied experimentally and theoretically in unsaturated, nonisothermal, salty soil;Fourier series were fitted to field temperature observations to estimate the temperature parameters, amplitude and phase angle of temperature wave, and heat flux phase at several harmonics. The temperature parameters and the heat flux phase were interpolated using the second and third-order Taylor series and cubic spline techniques. When considering the first harmonic alone, the cubic spline as an interpolation technique with nonuniform heat transfer theory provided the best estimate of soil thermal diffusivity. The Taylor series sometimes gave unrealistic negative thermal diffusivities. When using multi-harmonic analysis with nonuniform heat transfer theory, a method was suggested to calculate a combined value of thermal diffusivity. Although some individual harmonic thermal diffusivities were negative using the nonuniform soil analysis, the new method provided a single combined positive thermal diffusivity;Steady-state heat and mass transfer laboratory experiments were performed under boundary temperatures using unsaturated salinized and solute-free closed soil columns. Appreciable amounts of water moved in the direction of decreasing temperature within the soil columns. The net water transported to achieve steady-state conditions was greater for solute-free soil than for salinized soil;Theory describing both vapor and liquid phase moisture transfer in soil was developed. The theory extends previous work which only considered moisture and temperature gradients (Philip and De Vries theory) by also including solute concentration effects. The theory includes three diffusivities for the liquid phase and three diffusivities for the vapor phase. The liquid diffusivities were larger than the vapor diffusivities for the case studied. Water fluxes due to the temperature and solute concentration gradients were the most important fluxes for the salinized soil condition. Prediction of steady-state water distribution for the salinized soil conditions was made using the new theory for comparison with observation. The predictions compared well with the observed steady-state water distributions within the salinized soil column.</p>