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A novel approach to condensation modeling at the fin top of a grooved heat pipe

2019
Akdağ, Osman
Phase-change passive heat spreaders have the capability of carrying large amounts of heat from a heat source to a heat sink creating a small temperature difference. One common type of the passive heat spreaders is the heat pipes. The liquid flow inside a heat pipe is driven by the capillary pressure gradient created by a wick structure on the inner wall, which may be in the form of grooves, sintered grains or wire meshes. In the literature, grooved heat pipes are the most studied ones for modeling and experimentation due to their relatively simple geometry and ease of manufacturing. During the operation of a grooved heat pipe, continuous thin film condensation occurs on the fin top surfaces between two consecutive grooves and the condensate flows into the grooves. Modeling thin film condensation is crucial for an accurate estimation of grooved heat pipe performance. In the current study, a novel approach is developed to model the condensation and associated liquid flow in a fin-groove system. Conservation of mass and momentum equations, augmented Young-Laplace equation and Kucherov-Rikenglaz equation are solved simultaneously to calculate the film thickness profile. Differently from the numerical models in the literature, in this new approach the fin-groove corner is kept inside the solution domain and the effect of disjoining pressure is taken into account. The results reveal that the disjoining pressure may become effective for some cases and creates a textit{slope break} in the free surface of the liquid at the fin-groove corner. The current study presents the first numerical model which resolves the corner region and shows the effect of disjoining pressure on the thin film condensation in a fin-groove system. Furthermore, a parametric study is performed and the effects of geometric and thermophysical parameters on the condensation performance are discussed. Lastly, the thin film condensation in non-perpendicular fin-grooves, where the grooves are not rectangular but have inclined walls, is investigated and the effect of fin-groove corner on the condensation is presented.