Layer-by-layer assembled phase change composite with paraffin for heat spreader with enhanced cooling capacity

Highlights

• Layer-by-layer assembled phase change composite with 90 vol% paraffin is fabricated.

• Phase change composite shows up to 285 times higher thermal conductivities.

• Phase change heat spreaders lower hot spot temperature by ~7 °C, compared to aluminum.

Abstract

This study reports fabrication of layer-by-layer assembled phase change composites by locating phase change material (paraffin) into the network of aluminum meshes after which they are sandwiched by ultra-thin graphite sheets. The fabricated phase change composites with 90 vol% phase change materials exhibit up to 285 times higher thermal conductivities than bare paraffin with directional characteristics of heat flow due to the incorporation of graphite sheets which have anisotropic thermal conductivities. We further examine thermal performance of bare paraffin, aluminum, and phase change composite heat spreaders by monitoring maximum hot-spot temperatures under different cooling conditions. As a result, the phase change composite heat spreaders perform superior cooling capacities to bare paraffin and aluminum heat spreaders in high power intensity conditions with high heating and low cooling rates by lowering their hot-spot temperatures by up to 121 °C and 7 °C, respectively. It is enabled by the effective utilization of thermal capacitive effects of phase change materials with significantly enhanced thermal conductivities. This study represents an effort to develop novel heat spreaders with enhanced cooling capacities for the potential applications of high thermal budgets with limited cooling resources.

Introduction

As the power densities of electronic devices increase, effective thermal management is required, because excessive heat accumulation can considerably impair their performances. Recently, phase change materials have been highlighted as a new strategy for cooling electronic devices by employing their high thermal capacitance to effectively absorb the excess heat generated from the target devices [1], [2], [3], [4], [5], [6], [7], [8]. Paraffin is a good candidate in phase change materials for effective thermal management in electronics, because melting temperature of paraffin is not only tunable in the operation range of typical electronic devices, but also it has relatively large amount of heat of fusion [1], [2]. Particularly, filling the cavities among the fin arrays of heat sinks with paraffin resulted in the enhanced cooling performance with the lower peak temperature in the relatively high input power conditions, compared to control heat sinks [3], [4]. When paraffin was injected into the fin arrays of heat sink, the maximum temperature rise could be suppressed both for plate and pin fin heat sinks [5]. Fabricating heat sinks in aluminum blocks and subsequent infusion of paraffin enabled the decrease of the maximum temperature rise [6], [7]. Those studies employed the thermal conductive channels of heat sinks to enhance the thermal capacitive effects of phase change materials due to the low thermal conductivities of paraffin (~0.2 W/m·K). Thus, the thermal performance of the heat sinks integrated with paraffin was effectively enhanced by changing the configuration of heat sinks in terms of fin thickness and shape [8], [9] or fin spacing and arrangement [10].

To resolve those issues come from low thermal conductivities of paraffin, many studies demonstrated the development of composites with paraffin and thermal conductive fillers to enhance the cooling capacities of heat sinks based on phase change materials. Installing the paraffin infiltrated in copper foam in the base of heat sinks exhibited better cooling performance than control heat sinks with a pure copper base in intense heating conditions [11]. Expanded graphite and paraffin composites were attached to heat pipes to improve the cooling performance of battery [12]. Deploying the phase change composite with paraffin and multi-walled carbon nanotubes in the spaces among the fin arrays of the heat sinks lowered the peak temperatures of the hot spot, compared to bare heat sink cases, in relative high heating rates [13]. Albeit their successful demonstrations, those have mainly focused on enhancements of heat sinks based on the isotropic increase of thermal conductance of phase change composites, while limited attention has been paid to the incorporation of phase change materials to heat spreaders where the cooling characteristics of directional heat flow are preferred. Herein, we demonstrate the fabrication of layer-by-layer assembled phase change composites for enhanced thermal performance of heat spreaders. Specifically, the phase change composites are fabricated by infusing paraffin, a model phase change material in this study, into the network of an aluminum mesh, which is subsequently covered by ultra-thin graphite sheets. The fabricated phase change composites exhibit up to ~285 times higher thermal conductivities than bare paraffin in the designated direction with ~10 vol% inclusion of filler materials. We further employ the fabricated phase change composites to investigate the cooling performance of heat spreaders in different cooling conditions. The phase change composite heat spreaders perform superior cooling characteristics to bare paraffin and aluminum heat spreaders by showing the lowered hot-spot temperatures in intense heating conditions.