Thermal-Fluid Modeling For High Thermal Conductivity Heat Pipe Thermal Ground Planes

Abstract

The thermal ground plane (TGP) is an advanced planar heat pipe designed for cooling microelectronics in high gravitational fields. A thermal resistance model is developed to predict the thermal performance of the TGP, including the effects of the presence of non-condensable gases (NCGs). Viscous laminar flow pressure losses are predicted to determine the maximum heat load when the capillary limit is reached. This paper shows that the axial effective thermal conductivity of the TGP decreases when the substrate and/or wick are thicker and/or with the presence of NCGs. Moreover, it was demonstrated that the thermal-fluid model may be utilized to optimize the performance of the TGP by estimating the limits of wick thickness and vapor space thickness for a recognized internal volume of the TGP. The wick porosity plays a significant role on maximum heat transport capability. A large adverse gravitational field strongly decreases the maximum heat transport capability of the TGP. Axial effective thermal conductivity is mostly unaffected by the gravitational field. The maximum length of the TGP before reaching the capillary limit is inversely proportional to input power.

Research on a Simplified Model of an Aluminum Vapor Chamber in a Heat Dissipation System

“…In the numerical simulation calculation, it is assumed that the vapor chamber is working normally. In order to estimate the effective thermal conductivity for wick, Maxwell has presented Equation (14) that offers the thermal conductivity of such a heterogeneous material [28]. The effective thermal conductivity of the vapor chamber in the X, Y, and Z directions is calculated as Equations (15)- (17).…”

Simultaneous wick and fluid selection for the design of minimized-thermal-resistance vapor chambers under different operating conditions

“…This simplified modeling approach has proven effective in various studies [7,10,18,19] that have sought to explore the design space at low computational cost.…”

“…The expressions for wick and vapor core thermal resistance in equations (10) and (18), respectively, constitute the total thermal resistance imposed by the vapor chamber. From equation (19), it can be observed that besides its dependence on various wick, geometric, and operational parameters, the total thermal resistance is also a function of fluid properties, combined into liquid (Ml) and vapor (Mv) figures of merit.…”

“…Under these conditions, a higher Mv value is beneficial as it directly reduces the vapor core pressure drop; however, a higher Ml value also provides an indirect benefit because the same heat load can be supported using a thinner wick, thereby making a greater portion of the working thickness available to the vapor core. Analyzing the expression for the vapor core resistance in equation (18), at a given working thickness, Mv becomes prioritized in the extreme of low heat loads (for which the working thickness is primarily occupied by the vapor core) and Ml is prioritized in the extreme of high heat loads (for which a majority of the working thickness must be allotted to the wick). This tradeoff leads to the specific trends observed in Figure 2 (a) and (c), where the preferred fluid changes to that with a higher Ml as the heat load increases for a given working thickness.…”

Overview of Heat Pipe Studies During the Period 2010-2015

“…From a thermal point of view, the determination of the equivalent thermal conductivity of the capillary structure is even more difficult. It can be performed with a flash method, for instance (Ababneh et al, 2014), but the measured value takes into account only conduction through the capillary structure and does not consider evaporation or condensation phenomena. More sophisticated set-ups have to be developed to take into account these phenomena (Iverson et al, 2007) but there is a lack of experimental data and studies in this field.…”