Thin Two-Phase Heat Spreaders with Boiling Enhancement Microstructures for Thermal Management of Electronic Systems

Abstract

The current study goes over a design methodology for thin, two-phase heat spreaders for space constrained cooling applications. The evaporator section of the heat spreader employs enhancement structures to improve the spreader plate performance. The thermal performances of two such spreader prototypes, with integrated fins for cooling, were studied under both natural convection as well as forced air-cooled conditions. The results show a significant improvement in performance of the spreader plate compared to a solid metal plate subjected to similar boundary conditions. A design constraint on the evaporator and the condenser sections of the heat spreader ensures the enhanced structure remains flooded under all orientations, resulting in an orientation insensitive heat spreader. A predictive thermal performance model of the spreader plate was developed based on a semi-analytical model for boiling from structured surfaces. The semi-analytical model was validated against measured quantities from flow visualization studies reported in the literature and was found to predict the bubble departure diameter within ± 20 %, bubble frequency within ± 35 % and heat fluxes within ± 30 %. 2D numerical simulation, using level set formulation, was also carried out to understand the physics behind bubble departure from structured surfaces.