Waste Heat Recovery of Exhaust Gas in a Ribbed Double-Pipe Heat Exchanger

Abstract

The main contribution of this research study is to highlight the crucial role of radiating gas effect combined with circumferential ribs on the inner tube of a double-pipe heat exchanger to obtain higher thermal performance by recovering wasted heat for air heating. By taking the advantage of gases with higher radiative characteristics, significant performance improvement can be obtained by increasing the rate of heat transfer from participating hot exhaust gas flow to the cold air flow. This concept is demonstrated and verified by the numerical solution of the radiative transfer equation coupled with the set of conservation equations of energy, momentum, and continuity in steady-state conditions. The turbulent forced convection is solved by the well-known model to calculate the turbulent stress and heat flux. All computations are done by the COMSOL multi-physics software for a wide range of gas radiative properties in the double-pipe HE with and without ribs. The numerical findings reveal that the contributions of ribs and gas radiation effect in increasing the HE efficiency are 21% and 45%, respectively. In addition, by adding ribs into HE configuration, an increase of pressure drop of 1.76 and 0.71 Pa is observed for the gas and air flows, respectively.