Analysis of the thermal efficiency of solid and vacuum thermal insulation in an exchanger of the heat losses recovery system in mobile compressor units

Abstract

In this work, the developed methodology for the numerical analysis of the working process in the flow part of the recuperative shell-and-tube heat exchanger was tested and a comparative analysis of heat losses was carried out for different variants of external thermal insulation of the shell. According to the results of previous studies, solid insulation materials (mineral wool, basalt super fine fiber, polyethylene foam, foamed rubber, polyurethane foam) and vacuum and screen vacuum insulation were selected for the analysis.The analysis of working processes in the considered heat exchanger was carried out using a calculation technique based on the equations of thermal conductivity, convective heat exchange and heat exchange by radiation, as well as equations describing the motion of gas and liquid and their phase changes, contained in the ANSYS Fluent package. When modeling heat exchange processes, the following boundary conditions were are specified: the hot air inlet temperature Th is equal to 550 °C; water temperature at the inlet of the Tw is 10 °C; external ambient temperature Tex is 0 °C. The heat transfer coefficient α between the environment and the outer surface of the heat exchanger was assumed to be constant.According to the results of computational studies, we can draw the following conclusions: with regard to the object under consideration, thermal insulation allows reducing the amount of heat losses from 23% to ∼4%; The smallest losses from the investigated range of insulation are achieved using screen-vacuum insulation and its modification using screens of various degrees of blackness and quantity; for each type of insulation, as its thickness increases, losses are stabilized at a certain level, which leads to the absence of the need to increase the insulation thickness over 15 mm; even a 2 mm thermal insulation layer can significantly reduce heat loss; screening efficiency decreases with increasing number of screens (with a thermal insulation thickness of 20 mm, the efficiency of screen-vacuum insulation is approximately comparable to the efficiency of vacuum insulation with the same depth of vacuum).In this work, the developed methodology for the numerical analysis of the working process in the flow part of the recuperative shell-and-tube heat exchanger was tested and a comparative analysis of heat losses was carried out for different variants of external thermal insulation of the shell. According to the results of previous studies, solid insulation materials (mineral wool, basalt super fine fiber, polyethylene foam, foamed rubber, polyurethane foam) and vacuum and screen vacuum insulation were selected for the analysis.The analysis of working processes in the considered heat exchanger was carried out using a calculation technique based on the equations of thermal conductivity, convective heat exchange and heat exchange by radiation, as well as equations describing the motion of gas and liquid and their phase changes, contained in the ANSYS Fluent package. When modeling heat exchange processes, the following boundary conditions were are specified: the hot air inlet temperature Th is equal to 550 °C; ...