РАСЧЕТ ТОЛЩИНЫ ТЕПЛОИЗОЛЯЦИИ И ВЕЛИЧИНЫ ЗАГЛУБЛЕНИЯ ПОДЗЕМНЫХ ПОЛИЭТИЛЕНОВЫХ ТРУБОПРОВОДОВ ТЕПЛОСНАБЖЕНИЯ В РЕГИОНАХ С МНОГОЛЕТНЕМЕРЗЛЫМИ ГРУНТАМИ

Abstract

The process of thawing and freezing of the host soil of an underground polyethylene heat supply pipeline with thermal insulation, operated in areas of permafrost distribution, is considered. The task is to determine the thickness of the thermal insulation of the pipeline and the size of its depth based on the analysis of the temperature field in the ground during long-term cycle. The temperature field in the "insulated pipe-ground" system, which changes over time, is proposed to be determined by solving the heat conduction equations in polar coordinates. In this case, a bundle of pipes is considered as one pipe of equivalent radius. This approach allows to simplify the interface conditions of the pipe, thermal insulation, polyethylene shell and the host soil, as well as to use a simple numerical method for solving the equation – the finite difference method. The results of calculations of the maximum depth of soil thawing from the depth of the heat supply pipe at different thicknesses of thermal insulation are presented. It is proposed to determine the optimal depth of the underground heat supply pipeline from the condition of annual establishment of the zero isotherm of the host soil at the level of the boundary of the active soil layer by the beginning of the heating season. The possibility of finding a zero isotherm at this level is illustrated by calculations of isotherms by the beginning of the heating season (September) at various depths and thicknesses of thermal insulation. Based on the results of calculations the method of estimation the insulation thickness and depth of the pipeline from the condition of minimizing the functional that characterizes the measure of deviation of the ordinates of the zero isotherm on the left-hand boundary of the region from the depth of the active soil layer at the beginning of the heating season.