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

2016

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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

Section: Grooved Condenser Wick Domain Designmentioning

confidence: 99%

“…Recent research in vapor chamber design has focused on high-performance commercial and military electronics that require heat spreaders capable of dissipating high heat fluxes (over 500 W/cm 2 ) from small areas [1]. At such high heat fluxes, the wall superheat typically induces nucleate boiling in the evaporator wicks.…”

Section: Introductionmentioning

confidence: 99%

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

2016

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“…The heat flux dissipated ranges from < 10 W/cm 2 for applications such as portable electronics [1] to > 500 W/cm 2 for cooling of radar power amplifiers and high-performance computing systems [2]. Common among these applications is the need for thin, compact heat spreaders that accommodate transient heat loads.…”

Section: Introductionmentioning

confidence: 99%

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

2018

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Advances in the computational performance of electronic devices have created a clear need for improved methods of passive thermal management. This has led to renewed interest in the use of vapor chambers as heat spreaders in applications ranging from mobile devices to highperformance-computing and power electronics systems. While there has been significant effort to develop vapor chambers for these applications, their designs have largely relied on steady-state analyses and performance prediction. In many applications, however, the heat load is inherently transient in nature. Heat spreader design must consider transient performance in response to these use-case scenarios. While detailed numerical models of transient vapor chamber operation have been developed, a transient modeling approach with low computational cost is needed for parametric study and quick assessment of vapor chamber performance in system-level models.

“…Recent technology development has focused on vapor chamber designs for high-performance electronics requiring the dissipation of high heat fluxes (over 500 W/cm 2 ) [6]. The thermal resistance of such vapor chambers, as well as of more conventional vapor chambers with a 7 comparatively thick form factor, is dominated by the resistance across the wick at the evaporator.…”

Section: Introductionmentioning

confidence: 99%

Working-fluid selection for minimized thermal resistance in ultra-thin vapor chambers

2017

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The behavior of a vapor chamber is strongly coupled to the thermophysical properties of the working fluid within. It is well known that these properties limit the maximum power (heat load) at which a vapor chamber can operate, due to incidence of the capillary limit. At this limit, the available capillary pressure generated within the wick structure balances the total pressure drop incurred along the path of fluid flow within the wick. A common figure of merit prioritizes working fluids that maximize this capillary-limited operating power. The current work explores working fluid selection for ultra-thin vapor chambers based on a thermal performance objective, rather than for maximized power dissipation capability. A working fluid is sought in this case that provides the minimal thermal resistance while ensuring a capillary limit is not reached at the target operating power. A resistance-network-based model is used to develop a simple analytical relationship for the vapor chamber thermal resistance as a function of the working fluid properties, operating power, and geometry. At small thicknesses, the thermal resistance of vapor chambers becomes governed by the saturation temperature gradient in the vapor core, which is dependent on the thermophysical properties of the working fluid. To satisfy the performance objective, it is shown that the choice of working fluid cannot be based on a single figure of merit containing only fluid properties. Instead, the functional relationship for thermal resistance must be analyzed taking into account all operating and geometric parameters, in addition to the thermophysical fluid properties. Such an approach for choosing the working fluid is developed and demonstrated.Keywords: mobile device thermal management, ultra-thin vapor chamber, heat pipe, working fluid, figure of merit