INFLUENCE OF SOIL FILTRATION PROPERTIES ON THE WORKING CHARACTERISTICS OF THE VERTICAL GROUND HEAT EXCHANGER

Abstract

Introduction. The purpose of these studies is to determine the effect of the filtration properties of soil as a porous medium on the performance of soil heat exchangers. Ground heat exchangers are important elements of heat pumps widely used to extract low potential heat from ground masses. In the over whelming majority of scientific works related to the numerical modeling of the operation of ground heat exchangers, the soil is considered as a continuous medium and heat transfer in it occurs only by thermal conductivity. In reality, soil is a porous medium, the pores of which can be filled with air and liquid. In this regard, in addition to thermal conductivity, heat transfer in the soil can also occur by convection of liquids or gas in a porous medium. Results. This paper presents the results of numerical modeling of the temperature regime of the soil U-tube heat exchanger, taking into account the free convective movement of the medium filling the pores of the soil. The system of equations describing this process consists of the equations of fluid dynamics in a porous medium and the energy equation. Attached to them is the heat transfer equation in a U-tube heat exchanger. Based on the results of solving this system of equations, the distributions of velocity and temperature in the porous soil medium, as well as the change in the temperature of the heating agent in the heat exchanger, are determined. It has been determined that the maximum velocity of the free convection flow of water in the pores under the observed conditions is of the order of ~ 10-6 m/s. Evaluation of the energy performance of the ground heat exchanger depending on the size of soil particles and its porosity showed that a larger volume of recoverable heat is provided with a smaller particle size and lower porosity. It is also shown that when the pores of the soil are filled with water, a larger volume of heat is extracted from the soil in comparison with the case of filling the pores with air.