[Show abstract][Hide abstract] ABSTRACT: A 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.
International Journal of Heat and Mass Transfer. 01/2010;
[Show abstract][Hide abstract] ABSTRACT: The paper introduces the novel concept of using carbon nano tube (CNTs) based wick structures for high performance heat pipes and vapor chambers. This ongoing research aims to replace the copper wick structures with high conductive CNT wick structures. Individual carbon nanotubes possess extremely high thermal conductivities of the order of 2000-3000 W/m-K. With such a material as the wick in a heat pipe, the effective thermal conductivity of the fluid saturated wick will be significantly higher that a copper-based wick.
Semiconductor Thermal Measurement and Management Symposium, 2007. SEMI-THERM 2007. Twenty Third Annual IEEE; 04/2007
[Show abstract][Hide abstract] ABSTRACT: A numerical study is performed to characterize the thermal and mechanical performances of silicon/water vapor chambers as heat spreaders for electronics cooling applications and to compare their performance against Cu heat spreaders. 2D flow and energy equations are solved in the vapor and liquid regions, along with conduction in the wall. An equilibrium model for heat transfer and a Brinkman-Forchheimer extended Darcy model for fluid flow are solved in the wick region. In addition to thermal modeling, FEA is also performed to study the impact of the proposed design on die stresses. The study shows that this system can match or thermally perform better than a more standard Cu spreader while also reducing the compressive stress in the Si by as much as 96%. Analysis shows that there are two main factors contributing towards the reduction of stress in the Si die, namely, the better CTE match between the Si die and the Si heat spreader and higher compliance (less stiffness) of the vapor chamber compared to standard heat spreaders. Thus Si vapor chambers provide a good design alternative to a standard Cu heat spreader without compromising on the reliability and performance of the Si.
Semiconductor Thermal Measurement and Management Symposium, 2005 IEEE Twenty First Annual IEEE; 04/2005