Natural heating and cooling of intake air passing through fragmented strata

摘要

In this paper a study is performed to predict psychometric properties of intake air after it passes through a mass of pit muck (gathering area), which acts as a heat exchanger. The study is done on an area which maintains an air temperature about 2℃ all year round. This area contains broken rock and water that freezes in winter and melts in summer. The broken rock area may consist of one, two or three zones: the frozen zone, non-frozen zone, and ice zone at 0℃. In mid winter the upper rock layer is frozen whereas the broken rock at the bottom has a temperature few degrees above zero. In late summer all the rock has above zero temperature. The mine surface temperature changes according to the weather whereas the rock temperature at the bottom of the gathering area is assumed to be nearly constant the whole year. The Stephen Law is used to determine the location of 0℃ isotherm (the border between zones). The intake air moves through a system of capillaries. During ice melting these capillaries are the way for air and water. The amount of heat exchanged between fragmented strata and ventilated air in a capillary is governed by a theory involving the Reynolds, Biot, Nusselt, and Fourier numbers. The water from melted ice wets the capillaries changing the moisture content of the air and the amount of latent heat accompanied by a condensation or an evaporation process. In the ice covered zone, where the capillaries are considered dry, air temperature changes according to the dry surface conditions. The results presented in this paper are for the geological and average weather conditions prevailing in the Sudbury region.