Numerical analysis of flow characteristics and heat transfer of high-temperature exhaust gas through porous fins

摘要

Engine waste heat recovery technology based on thermodynamic cycles calls for highly compact and effective exhaust-gas heat exchangers, especially in the space-constrained applications. A porous funs heat exchanger was proposed and compared with the traditional solid fins heat exchanger in order to effectively enhance the heat transfer and realize the lightweight design. A three-dimensional model of the porous fins exhaust gas heat exchanger under forced convection has been developed and numerically investigated based on the Darcy-Forchheimer-Brinkman momentum equation and local thermal non-equilibrium energy equation. Computational studies are carried out to compare the hydraulic and thermal performance between the porous fins and solid fins of equal size at Reynolds number ranging from 5000 to 50,000. Results show that the porous fins heat exchanger greatly improves by 73.2-77.1% while brings an increase of 15.1-18.5% in the pressure drop. In terms of overall performance, the weight of porous fins heat exchanger is reduced by 90%, and the comprehensive performance factor measuring heat transfer and pressure drop is increased by 41% compared with solid fins heat exchanger. Subsequently, the effects of porous fins height, porous fins density, the porosity and pore density on the heat exchanger performances are also discussed. It is found that there is an optimal fin height to achieve the best comprehensive performance of porous fins heat exchanger.