A numerical model for transport in flat heat pipes considering wick microstructure effects

Abstract

a b s t r a c tA transient, three-dimensional model for thermal transport in heat pipes and vapor chambers is developed. The Navier-Stokes equations along with the energy equation are solved numerically for the liquid and vapor flows. A porous medium formulation is used for the wick region. Evaporation and condensation at the liquid-vapor interface are modeled using kinetic theory. The influence of the wick microstructure on evaporation and condensation mass fluxes at the liquid-vapor interface is accounted for by integrating a microstructure-level evaporation model (micromodel) with the device-level model (macromodel). Meniscus curvature at every location along the wick is calculated as a result of this coupling. The model accounts for the change in interfacial area in the wick pore, thin-film evaporation, and Marangoni convection effects during phase change at the liquid-vapor interface. The coupled model is used to predict the performance of a heat pipe with a screen-mesh wick, and the implications of the coupling employed are discussed.

Recent Advances in Vapor Chamber Transport Characterization for High-Heat-Flux Applications

“…This interface shape dictates the thickness of an extended thin-liquid film formed within the wick pores, and determines the local evaporation/condensation heat transfer characteristics. To capture these effects, Ranjan et al [160] developed a numerical approach wherein a macroscale device-level model was coupled with a sub-device microscale model that predicted meniscus shape and evaporation from a representative unit cell structure.…”

“…The device-level model used by Ranjan et al [160] was an adapted version of the flat heat pipe model originally developed by Vadakkan et al [109]. The mass, momentum, and energy equations are solved in the solid, porous, and vapor domains to determine the temperature and pressure fields within the device.…”

“…Therefore, Ranjan et al [160] developed correction factors to the interfacial area and evaporative mass flux to account for changing liquid-vapor interface shape, thin-film evaporation, and thermocapillary convection effects. In summary, the coupling procedure first computes the flow and temperature fields using the To evaluate the effects of microscale correction ratios on device performance, Ranjan et al [160] investigated the vapor chamber geometry shown in Figure 26, and solved for flow and temperature in the domain using the coupled model. Details of the boundary conditions imposed and the wick, liquid, and vapor thermophysical properties can be found in [160].…”

“…In summary, the coupling procedure first computes the flow and temperature fields using the To evaluate the effects of microscale correction ratios on device performance, Ranjan et al [160] investigated the vapor chamber geometry shown in Figure 26, and solved for flow and temperature in the domain using the coupled model. Details of the boundary conditions imposed and the wick, liquid, and vapor thermophysical properties can be found in [160]. As can be observed in Figure 26, the correction factors are maximized at the location of highest interfacial pressure difference at the center of the heat input, and decrease toward the condenser side.…”

Patterning the condenser-side wick in ultra-thin vapor chamber heat spreaders to improve skin temperature uniformity of mobile devices

“…The 2D geometry and case details ( Figure 2) are taken from Ref. [20]. The external dimensions are 30 mm × 3 mm, with a uniform copper wall thickness of 0.25 mm and a uniform wick thickness of 0.2 mm; the wick has porosity, permeability, and effective conductivity of 0.56, 2.97×10 -11 m 2 , and 40 W/mK, respectively.…”