Effective gas-to-gas heat exchanger by means of energy conversion between gas enthalpy and thermal radiation

Abstract

This paper presents the heat transfer characteristics of a new type of gas-to-gas heat exchanger that operates on the basis of energy conversion between gas enthalpy and thermal radiation. A theoretical analysis is conducted for the one-dimensional system where convection and radiation take place simultaneously in three porous layers. In the high-temperature section, the enthalpy of gas flow converts to thermal radiation and the reverse direction of this process occurs in two recovery sections. The porous medium is assumed to be a homogeneous continuum that absorbs, emits and scatters thermal radiation. In order to investigate the thermal behaviour of gas flows and porous layers, the coupled energy equations for the gas and porous media, based on a two-flux radiation model, are solved numerically using an iterative method. Computational results show that this type of heat exchanger has a very high efficiency, especially when the porous layers have a high optical thickness and a low scattering coefficient. To confirm the validity of the present analysis, the numerical results for a simple energy recovery system are compared with theoretical results of other investigators and reasonable agreement is found.