Direct Pore-Scale Simulations of Fully Periodic Unit Cells of Different Regular Lattices

Abstract

Open-cell metal foams are known for their superior heat dissipation capabilities. The morphological, pressure drop, and heat transfer characteristics of stochastic metal foams manufactured through traditional “foaming” processes are well established in the literature. However, employment of stochastic metal foams in next-generation heat exchangers is challenged by the irregularity in the pore- and fiber-geometries, limited control on the pore-volume, and an inherent necessity of a bonding agent between foam and the heat source. On the other hand, additive manufacturing (AM) is capable of printing complex user-defined unit cell topologies with customized fiber shapes directly on the substrates subjected to heat load. Moreover, the user-defined regular lattices are capable of exhibiting better thermal and mechanical properties than stochastic metal foams. In this paper, we present a numerical investigation on fully periodic unit-cells of three different topologies, that is, tetrakaidecahedron (TKD), rhombic-dodecahedron (DDC), and Octet with air as the working fluid. Pressure gradient, interfacial heat transfer coefficient, friction factor, and Nusselt number are reported for each topology. Rhombic-dodecahedron yielded the highest averaged interfacial heat transfer coefficient whereas Octet incurred the highest flow losses. Pore diameter, defined as the maximum diameter of a sphere passing through the polygonal openings of the structures, when used as the characteristic length scale for the presentation of Nusselt number and Reynolds number, resulted in a single trendline for all the three topologies.