A numerical investigation of heat transfer and pressure drop correlations in Gyroid and Diamond TPMS-based heat exchanger channels

The recent advances in metal additive manufacturing technologies have made TPMS (triply periodic minimal surface) structures a promising alternative for the design of heat exchangers. This numerical study has characterized the thermohydraulic performance of heat exchange channels based on Schwarz-diamond and Schoen-gyroid TPMS structures. The operating ranges applicable to molten salt reactor intermediate exchangers, which have been little studied in the existing literature, were investigated (2961 < Re < 18254; 3 < Pr < 5; 4 mm < d(h) < 12 mm). On the basis of these numerical calculations, two correlations were established to characterize the heat transfer coefficient and the friction factor of such flows. In addition to the classical dependencies observed for Reynolds and Prandtl numbers, an additional parameter was identified to characterize heat exchange, thereby accounting effects of wall boundary conditions. This parameter is defined as the ratio between the mean viscosity of the fluid and its viscosity evaluated at wall temperature. Moreover, the expressions obtained to characterize the Nusselt number and the friction factor are independent of the hydraulic diameter of the channels (serving as a characteristic length) and the density (or porosity) of the TPMS structures. Finally, while both structures exhibit comparable thermal performance, the Schwarz-diamond TPMS appears to be the optimal choice for heat exchanger application, as it involves less pressure drop than Schoen-gyroid TPMS.