Heat Transfer Analysis of Graphite Foam Embedded Vapor Chamber for Cooling of Power Electronics in Electric Vehicles

Abstract

The power density of power electronics in electric vehicles (EVs) is expected to be significantly enhanced, which would result in higher heat flux generation. Therefore, it is critical to find an efficient heat spreading and removal technology to reduce the junction temperature for high power density power electronics application. Vapor chamber using evaporation and condensation of the inside working fluid (i.e., water) as a heat spreader can remarkably improve the uniform heat spreading and heat removal for the power electronics compared to the traditional copper heat spreader. Furthermore, high thermal conductivity graphite foam (GF) would be embedded in the vapor core of the vapor chamber to further enhance the heat transfer performance. Numerical heat transfer simulations were performed for copper heat spreader, vapor chambers (with and without the presence of graphite foam) by using ANSYS. Various parametric effects on vapor chamber thermal performance were investigated, including the effects of heat flux from power electronics, heat transfer coefficient at heat sink, vapor chamber thickness, and graphite foam. Through the simulation studies, it was found that thinner vapor chamber (1.35 mm thickness) had better heat transfer performance than thicker vapor chamber (5 mm thickness) because of the extreme high effective thermal conductivities of ultra-thin vapor chamber. Furthermore, the effect of graphite foam on thermal performance improvement was very minor for ultra-thin vapor chamber, but significant for thick vapor chamber. The GF could help reduce the junction temperature by 15–30% in the 5-mm thick vapor chamber. Use of GF embedded vapor chamber could achieve 250–400 W/cm2 local heat removal for power electronics.