Numerical simulation of air heating by the recovered waste heat from the radiating exhaust gas flows in a plate heat exchanger

Abstract

The main idea comes from the fact that waste heat generated by the radiating combustion exhaust gas can be recovered by a plate heat exchanger to heat the air flow utilized in different applications. The main contribution of this study is to verify the effect of hot gas radiation and the inclination angle on the performance of plate heat exchangers. For this purpose, two counter-current flows of hot radiating exhaust gas and cold air separated with a conducting wall as the basis of a gas-to-gas plate heat exchanger (PHE) is numerically simulated in the transient period. In the gas domain, the combination of continuity and momentum equations are solved in the transient period up to the steady-state condition. The dimensionless form of the governing equations are solved simultaneously using the finite-difference method (FDM) and the Blocked-off technique, while the discrete ordinate method (DOM) is used to solve the radiative transfer equation (RTE) in the participating gas media. The results reveal that the gas radiation has a major role on the rate of heat transfer, such that by increasing the optical thickness from small to large values, a sweep behavior can be observed in the thermal performance of PHE. Furthermore, the rate of heat transfer increases significantly by increasing the radiation-conduction (RC) parameter, while the radiative effects of the hot flue gas on the pressure drop can be neglected without loss of accuracy. Moreover, the rate of heat transfer is not significantly affected by the inclination angle.