An analysis of temperature and moisture variations in the ground under natural climatic conditions

Abstract

The earth/ground is one of the main components of the thermal environment and contains water, more or less, in liquid and gas phases. The water in the ground has a great influence on the surroundings, especially on the surface temperature. It is needed to predict the moisture content profile in the ground soil and its surface, for exact consideration of the heat transfer in and on ground soil. The moisture content in the ground soil is strongly influenced by precipitation and the depth of the water table in the ground. The heat and moisture (vapor and liquid water) transfer considerably affect each other. For prediction of the temperature and the moisture content profile in the ground, simultaneous transport of heat and moisture can be considered. This paper presents the results of transient analysis of the heat and moisture fields in the earth/ground under precipitation with non-linear simultaneous heat and moisture transfer equations using the water chemical potential as the potential of the surroundings. Using the weather data of Osaka, Japan, variations of moisture content and temperature in and on the earth/ground are numerically analyzed. An evaporation/condensation process is analyzed quantitatively. The transient process of surface moisture content and water chemical potential are shown. These values vary strongly but never reach saturation in the case of the sandy soil. Average moisture content in the earth/ground is strongly affected by the annual average precipitation but little by the depth of the water table. Using these results, thermal behavior of the thermal well and method of analysis are discussed. For analysis, approximation of the side boundary condition by uniform moisture content is applicable in two-dimensional analysis within the medium moisture content. And for practical calculation, approximation by a linear simple heat diffusion equation is applicable.