Patterns of air temperature changes in air ducts of non-contact air heating or cooling systems

Abstract

The article is devoted to the study of the patterns of changes in air temperature during its movement in a sheet steel air duct during the operation of non-contact air heating systems, when the temperature of the moving air through the duct is higher than the room air temperature, as well as in the process of non-contact air cooling, when the temperature of the moving air in the duct below the room temperature. Based on the mathematical model of the ongoing physical processes developed in the article, an analytical formula is derived that allows, taking into account the presence of a heat-insulating layer or without it, to determine the patterns of changes in the temperature of moving air through the air duct at a given distance, depending on the thickness of the wall of the air duct and the speed of its movement. A dependence is given that determines the value of the heat transfer coefficient of air moving inside the duct to the inner surface of the duct on the speed, which at a constant flow rate is presented as a dependence of heat transfer on the open cross-sectional area of the duct. An analysis was carried out of the change in temperature of the moving volume of air inside the duct as a result of heat exchange with the surrounding air. A comparative calculation of the change in temperature of air moving in a thermally insulated air duct and in an air duct without thermal insulation was performed. The necessity of carrying out a calculation to determine the patterns of changes in the temperature of moving air inside the air duct when designing air heating systems or air conditioning systems is substantiated. It is concluded that it is necessary to conduct a technical and economic analysis on the feasibility of installing thermal insulation of air ducts made of thin sheet steel.