An experimental study of coupled heat and moisture transfer in soils at high temperature conditions for a medium coarse soil

Abstract

A study of one-dimensional heat and moisture transfer within a vertical soil column was conducted experimentally. An experimental soil cell made of stainless-steel tube was exposed to differential heating by sandwiching it between two differentially-heated plates for studying heat and moisture transfer in the soil column at different temperature levels and temperature differences. The main objective of the experimental study was to investigate heat and moisture transfer characteristics in a medium coarse soil at temperatures greater than 40 °C up to 90 °C. In this paper, the results are divided into two parts. In the first part, the results of heat transfer in dry soil are presented and discussed. The purpose was to investigate temperature distributions and heat gains/losses at the steady-state conditions along the soil cell at the various temperature levels. In the second part, the results of heat and moisture transfer in wet soil are presented and discussed. In this part, the transient temperatures, moisture contents and thermal properties along the soil column were obtained using the heat pulse technique. A loamy sand with a porosity and an initial water content of 0.40 and 0.26 m3/m3 (or saturation degree of 65%), respectively, was used in the study. The results of the case with the largest temperature difference of 65 °C (or overall temperature gradient of 440 °C/m) and the mean temperature of 55 °C are presented in detail. The highest temperature gradient of 1450 °C/m was recorded at the top of the soil column during the test, driving downward a moisture flux as high as 3 g/s·m2 when the soil was at temperature of 51 °C and saturation degree of 40%. Under these conditions, the thermal vapor diffusion is the main mechanism for the moisture flux.