Manufacturing complex shapes is now possible with the advent of industrialized metal three-dimensional (3D) printing machines. Three-dimensional printed parts are no longer limited to building prototypes. With the technology's progress and maturity over the past decade, a small-to-medium volume production is an option. It is expected that the high-valued customized components will be mainly manufactured with this method. Among industrial components, 3D printing of highly efficient heat exchangers (HXs) seems to be a plausible choice. 3D printing of heat exchangers in metals with high thermal conductivity is of particular interest due to the high heat exchange rate. Among the commercially available metals, aluminum and copper are adequate candidates. Also, increasing the HXs surface area within the same designed volume can be translated into higher efficiency if HXs are appropriately designed. To this end, the design, optimization, and manufacturing of Triply Periodic Minimal Surface (TPMS) with the designed hydraulic diameter of an order of mini/micro-channel tubes are proposed. TPMS structures are known to fill the space with a very high surface area. These labyrinth-like structures can be customized to accommodate two working fluids without mixing. Therefore, additive manufacturing of the TPMS structure is an option to investigate. However, TPMS structure requires to be designed and optimized through the numerical simulation firsthand to know about their heat transfer enhancement potential. TPMS structures have many different forms. Among them are Gyroid, Diamond, and Schwarz-D surfaces. TPMS efficiency has been compared with Performance Evaluation Criteria (PEC), a global goodness factor. PEC is the heat transfer coefficient ratio between the enhanced surface geometry and the smooth reference channel at the constant power consumption. Considering that every HX is made of three sections (inlet and outlet manifold and core section), each part has been optimized to ensure that the nominal performance is maintained throughout the HX. Single-phase numerical simulations are conducted for both laminar and turbulent flow utilizing water as a test fluid. The effect of conduction through HXs walls has been taken into account (i.e., conjugate heat transfer analysis). Before the single-phase numerical calculation, the Design of Experiment (DOE) matrix is going to be utilized to obtain the set of data sets that give the optimal surface parameters. Additionally, commercial numerical tools are equipped with the optimization algorithm named adjoint solver, which is further implemented to optimize the topology. While this study is limited to numerical investigation, the geometry parameters in the optimization process have been varied within the range of fabrication feasibility using conventional metal 3D printers. Finally, a general correlation based on non-dimensional parameters has been developed using numerical solutions data points.