## 1 Introduction
### Literature Review
#### 1.2.3 Combined Surface Roughness and Porous Structure in Additive Manufacturing  
Additive manufacturing (AM), particularly 3D printing techniques, offers unprecedented control over complex geometries, enabling the creation of surfaces that simultaneously incorporate optimized roughness, tailored porosity, and intricate macro- and microstructures. Advancements in utilizing additive manufacturing (AM) to leverage these combined effects have been researched. For instance, [PERSON] et al. [29] experimented with boiling heat transfer using SLM-fabricated AlSi10 Mg groove structures. Their pool-boiling experiments with de-ionized water showed significant increases in boiling HTC and CHF compared to smooth surfaces, with an optimal groove length of 2.2 mm, which saw an increase in CHF (3.1 times improvement) and HTC (2 times improvement). Increasing groove height, however, decreased performance due to increased flow resistance. The combination of groove geometry and semi-melted surface powder facilitated vapor-liquid flow and separation, effectively enhancing heat transfer. [PERSON] et al. [30] investigated controllable grid structures on stainless steel surfaces created using laser-based powder bed fusion. Experiments demonstrated that these grid structures significantly increased CHF, with the optimal performance observed in a 0.5 mm grid width sample, yielding a 10-27% CHF improvement (from 63.3 W/cm\({}^{2}\) to 93.9 W/cm\({}^{2}\)) over other samples. [PERSON] et al. [31] experimentally investigated saturated pool-boiling heat transfer using micro-structured surfaces fabricated via selective laser melting (SLM) from AlSi10 Mg powder, testing them with FC-72 as the coolant. Compared to a plain Al-6061 surface, their SLM-produced micro-structured surfaces significantly enhanced heat transfer performance. A maximum HTC of 1.27 W/cm\({}^{2}\).K was achieved, representing a 70% improvement. Additionally, the highest CHF achieved was 47.90 W/cm\({}^{2}\), a 76% enhancement over the plain surface. This improved performance was attributed to the inherent surface grooves and cavities created by the laser-melting process, which act as effective nucleation sites and facilitate thermal transport. [PERSON] et al. [32] explored the application of SLM to design and manufacture porous fin arrays directly onto copper bases. They determined that the one-layer porous fin structure achieved a CHF of 3122 kW/m\({}^{2}\), representing an 86% enhancement. In comparison, the two-layer structure demonstrated stable boiling up to 4532 kW/m\({}^{2}\) without reaching CHF (an over 170% enhancement) within the experimental limit. The highest HTC for the one-layer structure was 175 kW/m\({}^{2}\).K (80% enhancement), and for the two-layer structure, it was 163.8 kW/m\({}^{2}\).K (67% enhancement). This superior performance was attributed to numerous nucleation sites, increased heat transfer area, capillary-assisted suction, and separate liquid and vapor pathways. [PERSON] and [PERSON] [33] experimentally investigated pool boiling on hierarchical copper micro-porous structures fabricated by sintering spherical copper powder. While un-patterned surfaces increased the CHF by over 220%, they caused high superheat due to partial dry-out. Machining channels into these surfaces dramatically improved the CHF by 412% with a much lower superheat (49 \({}^{\circ}\)C), enabling vapor escape and separating liquid and vapor flow. Both micro-porous layer thickness and channel depth were critical. Thicker, un-patterned layers increased the CHF (1.5 mm yielded a 3.2-fold enhancement over flat), while thinner layers (0.3 mm) showed a superior HTC (a 3.7-fold enhancement). [PERSON] et al. [34] utilized SLM to create honeycomb fin structures with microscale side gaps on AlSi10 Mg surfaces, aiming to enhance pool boiling with a Novec 7100. These modifications eliminated boiling incipience hysteresis and improved liquid replenishment by introducing new vapor-liquid flow paths.