Conjugated heat transfer analysis of a foam filled double-pipe heat exchanger for high-temperature application

Abstract

A numerical investigation is performed to analyze the high-temperature heat transfer behavior in a double-pipe heat exchanger filled with open-cell porous foam. The Forchheimer-extended Darcy equation and the local thermal non-equilibrium model are utilized to simulate the flow and thermal transport inside the foam regions, considering the coupling effects between the inner and annular spaces. The effect of solid wall thickness is incorporated in the modelling process, following the continuity conditions of temperature and heat flux at the porous-solid interface. Simulations are conducted for a counter-flow heat exchanger while the thermal radiation transfer is solved using the P1 approximation. The cold fluid flows in the inner pipe, whereas the hot fluid in the annular gap. The temperature distribution, pressure drop, heat exchanger effectiveness and the overall performance are predicted. Effects of thermal radiation, foam structural parameters and the heat exchanger size are examined. The results indicate that thermal radiation promotes the thermal exchange between the two fluid sides. The heat exchanger effectiveness is improved by decreasing the porosity or increasing the pore density, exchanger length and annulus dimension, however, the potential increase in the total pressure drop should be seriously considered. Besides, the overall performance is slightly improved by further increasing the exchanger length when the dimensionless length is greater than 35.