Hook-shaped structures to improve pool boiling heat transfer

Boiling performance while using raised hook-shaped metal features, manufactured from copper by a skiving process, was investigated and compared with the boiling performance of a bare copper surface. Deionized water at the saturated conditions at 1 atm was used as the working medium. These fins can potentially improve the performance of immersion cooling spreaders in power electronics applications. The advantages of this technology compared with other methods presented in the literature include its scalability, low cost, resistance to erosion and clogging, and the industrialization of the manufacturing method. Four GRIPMetal hooked surfaces were investigated, each with different profiles (i.e., metal features, heights, and spacing) induced by the manufacturing process. The results show that the surface with hooks had lower wall superheat at the onset of nucleate boiling (ONB) compared with the bare surface. This appears to be due to the surface cavities—i.e., the negative potions of the raised hooks created by the skiving process, which helped initiate bubbles earlier. Moreover, the heat transfer coefficient (HTC) was superior for all surfaces with hooks at low heat fluxes because of increased surface area and enhanced bubble dynamics offered by the arrangement of the hooks. The hooked surface achieved a maximum HTC of 8.9 W/cm2K, which represents a 96 % enhancement ratio over the bare surface. The surface area increase (At/Abare) offered by the proposed hooks and their corresponding grooves was measured using the photogrammetry technique and was found to range from 1.35 to 1.8. Lastly, the critical heat flux (CHF) was significantly enhanced, reaching a 67 % increase over the bare surface; this is attributed to the available bare inter-fin area that can supply the liquid to the nucleation sites and the assisted suction flow through the front of the grooves.