Transient numerical analysis of a multi-layered porous heat exchanger including gas radiation effects

Thermal characteristics of a new type of multi-layered porous heat exchanger (PHE) are identified in the present study. This system works based on the energy conversion between gas enthalpy and thermal radiation. It has a five-layered structure consisting of two high temperature, two heat recovery and one low temperature sections. These sections are separated from each other by four quartz glass windows. In the two high temperature sections, the enthalpy of high temperature gas flow is converted to thermal radiation that is emitted toward the three adjacent layers where the low temperature air flows are effectively heated by the reverse conversion from thermal radiation into gas enthalpy. The gaseous radiation is also considered, such that in each section, a transient theoretical analysis is conducted for a one-dimensional system where convection, conduction and radiation take place simultaneously in both gas and solid phases. The coupled energy equations for the gas flows and porous layers based oil the two-flux radiation model are solved numerically to identify the transient heat transfer characteristics of the system. It is shown that this type of porous heat exchanger has a very high efficiency especially when the porous layers have high optical thicknesses. (C) 2008 Elsevier Masson SAS. All rights reserved.