Heat transfer in BCC lattice materials: Conduction, convection, and radiation

Research studies have recently been conducted on heat transfer in architected materials. As a type of rationally-designed lightweight material, lattices have received much attention in the past few years due to their multifunctional properties, mainly realized by the application of 3D printing techniques. In the present research, fluid flow and conduction, convection, and radiation heat transfer in three-dimensional periodic BCC lattices, as a topologically cubic example among a myriad of cellular architectures, are studied for a wide range of porosity (0.7–0.99) and Reynolds numbers (1–150) via a CFD analysis. The steady and incompressible flow of cool fluid with constant thermophysical properties inside a unit cell or an assembly of unit cells is simulated using the Fluent software. First, the hydrodynamic behavior of the fluid flow in the unit cell without a thermal gradient is studied. In the absence of radiation, conduction and convection heat transfer are explored under two different thermal conditions, namely Constant temperature at solid struts and Constant heat release from solid struts. The numerical results show that cell temperature increases for the constant temperature boundary condition and decreases for the constant heat release when the cell porosity decreases at the same Reynolds number. By considering radiation mechanism via the Discrete Ordinates Method, it is observed that radiative thermal conductivity increases by increasing the porosity. The increase, linearly correlated with the cell size, slightly enhances by increasing the solid radiative emission coefficient and the applied temperature difference. At lower porosities, the heat conduction, and at higher porosities, the radiation heat transfer plays a significant role in the effective thermal conductivity. At the average cell temperature of 1800 K, the ratio of radiative thermal conductivity to the effective thermal conductivity is 95% for the porosity of 0.99 and is 12% for the porosity of 0.7. After examining all three modes of heat transfer at the constant heat release thermal condition, it is found that the temperature of solid struts increases by decreasing the Reynolds number, leading to an increase of the ratio of radiation heat transfer to the total heat transfer (the ratio rises six times as the Reynolds number decreases from 150 to 1.5625 for the porosity of 0.99). For the constant heat release thermal condition, radiation heat transfer in BCC lattices can not be ignored when the porosity is high or the thermal conductivity of constitutive solid and the flow Reynolds number are low.