Advancements in additive manufacturing (AM) technology have enabled the use of Triply Periodic Minimal Surface (TPMS) lattice structures to integrate thermal and structural functions into a single component. These structures offer advantages such as weight reduction, compactness and enhanced heat dissipation, making them promising for automotive, aerospace and electronics applications. TPMS structures, characterized by zero mean curvature and periodic crystalline geometry, have recently gained significant research attention thanks to their potential in thermal management. Among various TPMS geometries, the gyroid and diamond structures stand out for their thermal and fluid dynamic performance. This study explores the influence of cell geometry, unit cell size, and wall thickness on the efficiency of TPMS-based heat exchangers, as these parameters are crucial for their technical feasibility. Using Computational Fluid Dynamics (CFD) simulations, a comparative analysis is conducted for a case study represented by a heat exchanger. The numerical approach relies on a steady-state Reynolds-Averaged Navier-Stokes (RANS) approach with the Reynolds Stress Transport (RST) Elliptic Blending model, while heat transfer is analyzed through the Conjugate Heat Transfer (CHT) technique. The results indicate that reducing the unit cell size enhances heat transfer but also increases pressure drop at a fixed flow rate. Similarly, increasing the wall thickness raises pressure losses, though its effect on heat transfer is minimal. Overall, the diamond structure outperforms the gyroid in both thermal efficiency and flow permeability, making it a more effective choice for TPMS-based heat exchangers. These findings offer valuable insights for optimizing TPMS geometries in high-performance heat transfer applications, guiding future research and industrial implementations.