On the Influence of Water-Ice Phase Transitions in Clay Soil Bases on the Heat Loses of a Building

Abstract

The article discusses the features of heat transfer in soil foundations under buildings associated with the presence of water in the soil. The objective of the study was to show the influence of the heat of phase transitions occurring during freezing and thawing of water on heat losses from the building to the ground foundation. The studies were carried out by setting up computational experiments based on calculations of nonsteady temperature fields in the soil. The annual cycles of atmospheric air temperature change were considered, which determine the global non-stationarity of heat transfer in the ground. To solve the problem, a physical and mathematical model of heat and mass transfer was used, considering the transfer of ground moisture, phase transitions in water, and changes in time in the values of the thermal characteristics of the soil - the coefficient of thermal conductivity and specific heat capacity. To take into account ice formation, semi­empirical dependences of the relative ice content of soils on their temperature and moisture were obtained. By means of computational experiments, the influence of ice formation in the soil is analyzed in comparison with calculations in which ice formation is not taken into account. It has been established that ice formation leads to temperature changes in the near-surface layers of the soil with a thickness greater than the thickness of its freezing. These changes can be up to several degrees Celsius and can exist for six months from the beginning of soil freezing. It has been established that ice formation does not lead to significant additional heat losses from the building to the ground foundation. The change in heat losses during the heating period and for the year is not significant. But at the same time, relatively small, within a few percent, changes in the maximum and minimum average daily values of heat fluxes take place. These average daily deviations occur with limited ground distances between indoor and outdoor air within 3-4 m.