Thermo–hydraulic performance of hybrid lattice-based heat exchangers for supercritical CO2 waste heat recovery cycles

Advances in additive manufacturing have enabled the development of complex heat exchangers with strong potential for supercritical CO 2 (S-CO 2 ) power cycles and waste heat recovery applications. This study investigates novel hybrid TPMS-based heat exchangers by combining two base topologies, Schwarz-Primitive and Gyroid, with Diamond, Octet, and Body-Centered Cubic lattice structures. Two integration strategies are considered to introduce an innovative class of interpenetrating architectures: full integration across the heat exchanger domain, and partial integration selectively confined to a single fluid domain. Three-dimensional conjugate heat transfer analyses are conducted for 48 configurations with different volume-fraction combinations. The baseline-geometry results were compared with experimentally-validated reference data to assess the accuracy of the numerical model. The results for the hybrid configurations are compared against their pure TPMS counterparts to evaluate the effects of lattice hybridization on heat transfer, pressure loss, and overall thermo–hydraulic performance. The results indicate that, for the investigated designs, partial integration reduces the frictional penalty in the unobstructed fluid domain compared with full integration. In the partial-integration configurations, the secondary lattice is placed in the S-CO 2 domain for the Schwarz-Primitive base and in the cooling-water domain for the Gyroid base, leaving the opposing fluid domain unobstructed. Among the investigated designs, the partially integrated Schwarz-Primitive-Diamond configuration achieved the highest overall thermo–hydraulic performance, with a performance evaluation criterion of 4.52, corresponding to a 3.5-times improvement relative to a smooth-tube reference. Overall, the findings demonstrate that hybrid TPMS-lattice architectures provide a flexible design strategy for tailoring S-CO 2 pre-coolers toward maximum thermo–hydraulic efficiency.