Fluid flow and heat transfer characteristics of octet truss lattice geometry

Octet truss lattice structures are a potential candidate for developing multifunctional heat exchangers/sinks owing to their superior structural characteristics compared against stochastic open-cellular metal foams. Structural efficiency is achieved primarily due to increased nodal connectivity in octet-truss lattices. Designed octet trusses and periodic cellular materials, in general, lend themselves well to topology optimization and integration of multiple functions enabling a high degree of tailorability and superior performance benefits. Specific to heat transfer design, octet truss lattices can be tailored to achieve optimal strand cross-sectional area to -length ratio for improved effective thermal conductivity while meeting surface-area per volume requirements for convective transport. In this work, we explore the heat and fluid flow characteristics using direct numerical simulations of a periodic unit-cell. Effective thermal conductivity, permeability, inertial coefficient, friction factor and Nusselt number for octet truss lattice structures are predicted and compared against stochastic foam experimental data. A range of porosities and pore densities are simulated and heat transfer and fluid flow characteristics are correlated using a single length scale in the form of Brinkman screening length, root K, as against existing literature where different geometric length scales are used. Further, octet truss lattice geometry is compared against existing stochastic metal foam heat and fluid flow empirical data. Normalized permeability of octet lattices were found to be 20-80% higher than stochastic foam for a given porosity. Similarly, for a fixed porosity, inertial coefficients of octet lattices were 50% of stochastic experimental measurements. For the range of Reynolds number considered, octet truss lattices show similar fluid and heat flow characteristics if not better performance than stochastic foams and thus making them ideally suited for tailored multifunctional heat sinks and exchangers.