Enhanced heat transfer in sandwich heat transfer unit with metal foam: A numerical investigation

In this study, a novel configuration of a sandwich heat transfer unit (SHTU) is proposed, characterized by the partial filling of metal foam on both sides of the fin. The thermal-hydraulic characteristics of the SHTU are investigated numerically using the local non-equilibrium method and Forchheimer-Brinkman extended Darcy model, and compared with those of traditional flat plate-fin heat transfer unit (PHTU). The effect of geometrical parameters, mass distribution of fin and metal foam, and morphological parameters of metal foam on the characteristic of SHTU was explored. Compared to PHTU the Nusselt number of SHTU increases by 13.1% and 27.6%, while the friction factor increases by 6.2% and 33.1% at Reynolds numbers of 100 and 900, respectively. At a Reynolds number of 500, as the filling ratio increases from 0 to 0.95, the Nusselt number, friction factor, and comprehensive thermal performance enhancement increase by factors of 10, 20, and 3, respectively. When the foam fraction increases from 0.30 to 0.90, the thermal performance enhancement improves by 4-5 times within the investigated range. The impact of porosity (e) and pore density (w) on the performance of SHTU is not monotonic. The optimal w was observed to be in the range of 15-20 PPI, while the optimal e was found between 0.90-0.92.