Preliminary CFD analysis on the effects of conjugate problems for a smooth duct and a Kagome lattice channel: average results for heat transfer and pressure losses

The compactness of electronic devices and mechanical components and the constant increase in power density pose significant challenges in thermal management. These geometric constraints imply the reduced length of the channels dedicated to their cooling, hence the need to properly analyze the conjugate heat transfer problem and develop new innovative heat dissipation systems, such as lattice structures. This paper aims to numerically investigate the thermo-fluid dynamics properties of a short empty duct 80 mm long, named K0, with a cross-section of 15x5 mm in two different flow conditions: fully developed and developing flow. Then, the same channel is equipped with a Kagome-truss lattice with a truss diameter of 0.8 mm, named K1 and characterized by a porosity 휙=87%, and the analysis is repeated for both outflow conditions. The thermal fluid is air, and the operating Reynolds numbers range from 2852 to 17115 for all the studied cases, thus falling within the transitional flow regime. Results for the smooth duct show its sensitivity to flow conditions, revealing a substantial increase in the Nusselt number by up to 13% at the cost of a higher friction factor, as is expected from existing studies in the literature. On the contrary, no significant variation in friction factor and Nusselt number is observed for the K1, suggesting that its thermo-fluid dynamic properties are more influenced by the lattice structure rather than the flow profile. Finally, the two ducts are compared in terms of energy efficiency, evaluated as Nu/λ1/3, revealing that at the same Reynolds number, the efficiency of the Kagome duct is up to 2.2 and 2.4 times greater than that of the empty duct in fully developed and developing flow condition respectively.