Heat transfer capacity optimization design of microgroove and microcolumn in an ultra-thin flat heat pipe

Abstract

Ultra-thin flat heat pipes (UFHPs) are being explored as a potential thermal management solution to address the heat dissipation challenges of electronic devices. However, the ultra-thin process increases fluid flow resistance and reduces the heat transfer capacity, posing challenges for wick structure optimization. In this study, the effects of wick structure, vapor space, and fluid flow properties on the maximum heat transfer capacity are analyzed by a fluid flow model. Microgroove and microcolumn as wick structures are optimized, and the coupling effects between capillary pressure and fluid flow resistances are analyzed. The maximum heat transfer capacity and the corresponding optimal wick structure dimensions are determined by the vapor space friction and wick structure friction, which are calculated by structural friction coefficients (S_v and S_l) and fluid friction coefficients (F_v and F_l). The models of fluid flow friction chosen in previous literature are validated for accuracy by Fluent. When the height of the wick structure (h) or vapor space (H) increases, the optimal dimensionless wick structure height (h*) increases and decreases under a fixed porosity (ε), respectively. The optimal h* of microgroove decreases and that of microcolumn increases as the dimensionless spacing (l*) increases. When ethanol is used as the working fluid, the optimal h* of microgroove is 1.98 and the optimal h* of microcolumn is 0.48, under the condition of H = 0.3 mm, h = 0.15 mm, and ε = 0.5. This model also emphasizes the importance of working fluid properties on the design of the wick structure, and a higher value of F_l/F_v results in a lower optimal h*. Moreover, methanol and acetone exhibit higher heat transfer capacity compared with ethanol. This study aims to provide comprehensive design principles for optimizing UFHP heat transfer capacity.