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

Abstract

Vapor chamber technologies offer an attractive approach for passive heat spreading in mobile electronic devices, in which meeting the demand for increased functionality and performance is hampered by a reliance on conventional conductive heat spreaders. However, market trends in device thickness mandate that vapor chambers be designed to operate effectively at ultra-thin (sub-millimeter) thicknesses. At these form factors, the lateral thermal resistance of vapor chambers is governed by the saturation temperature/pressure gradient in the confined vapor core.In addition, thermal management requirements of mobile electronic devices are increasingly governed by user comfort; heat spreading technologies must be designed specifically to mitigate hot spots on the device skin. The current work considers these unique transport limitations and thermal requirements encountered in mobile applications, and develops a methodology for the design of vapor chambers to yield improved condenser-side temperature uniformity at ultra-thin form factors. Unlike previous approaches that have focused on designing evaporator-side wicks for reduced thermal resistance and delayed dryout at higher operating powers, the current work focuses on manipulating the condenser-side wick to improve lateral heat spreading. The proposed condenser-side wick designs are evaluated using a 3D numerical vapor chamber * Corresponding author: Tel. 765 494 5621 ; sureshg@purdue.edu 2 transport model that accurately captures conjugate heat transport, phase change at the liquidvapor interface, and pressurization of the vapor core due to evaporation. A biporous condenserside wick design is proposed that facilitates a thicker vapor core, and thereby reduces the condenser surface peak-to-mean temperature difference by 37% relative to a monolithic wick structure.Keywords: mobile device thermal management, vapor chamber, heat pipe, ultra-thin, sintered wick, patterned condenser wick

A validated time-stepping analytical model for 3D transient vapor chamber transport

“…The complete transient behavior of Case #1 was simulated using variable time-steps in the range of 0.1 s to 2 s. Case #2 was simulated to obtain a comparison at steady-state, using the steady-stateseeking solution algorithm described in Ref. [3]. The simulation with the time-stepping analytical model uses a time step of 0.1 s for both the simulations.…”

“…Previous work in designing vapor chambers for mobile devices has been limited to a consideration of steady-state operation [3]. Evaluation of vapor chambers for mobile devices and other applications will require transport models capable of efficiently computing the temperature field for transient boundary conditions and thin form factors.…”

“…For example, Patankar et al [3] used a numerical vapor chamber model to analyze the steady-state performance of ultra-thin vapor chambers for mobile thermal management applications; due to the large computational cost, a steady-state-seeking solution procedure had to be adopted to bypass the physical transient behavior. Such numerical models are best suited to single-point evaluation of single device designs.…”

Experimental Development and Computational Optimization of Flat Heat Pipes for CubeSat Applications

“…Heat fluxes up to 330 W/cm 2 and thermal conductivities as high as 2,100 W/m-K were measured. Other studies have focused on enhancing the characteristics of the evaporator and condenser wicks [7][8][9][10]. However, relatively limited research has specifically focused on CubeSat applications.…”

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

“…A higher value of Mv yields a lower vapor core thermal resistance at a given thickness. [12][13][14][15][16], or even achieving desired temperature profiles on the condenser side [17]. However, the implications of wick properties on choosing a wick for minimization of the total thermal resistance of the vapor chamber have not been systematically explored in the literature.…”