Phase Transition Behavior of Thin Film Phase Change Materials

Phase change materials (PCMs) offer opportunity for passive cooling by utilizing their favorable thermal properties to absorb and release energy through phase transitions, most commonly solid to liquid. PCMs have been studied for use in various heat sink and heat exchanger designs to provide secondary cooling relief or as energy storage vessels. In most of these applications, the PCMs are applied to the system in large quantities and are configured in designs that allow natural convection to develop due to the thermal gradients across the thermal management system. The relationship between the different heat transfer modes in this system make the melt progression difficult to predict and track. Early PCM heat transfer occurs only as conduction due to the lack of sufficient liquid phase to facilitate convection current formation. Once melting yields significant liquid phase, natural convection occurs and becomes the driving heat transfer mechanism based on heat generation distribution and buoyancy. Thin film PCMs are PCMs that are applied as thin layer to effectively reduce one dimension, resulting in prevention of convection current formation. This forces the PCM to melt or solidify entirely through conduction heat transfer and allows the thermal properties of PCMs to be analyzed experimentally without the highly variable nature of convection currents impacting the melting region. This effort has designed a thin film PCM test apparatus and procedure for analyzing the impact of thermal properties on the melt progression across the thin film. Localized heating of PCMs remains an important design consideration for many current electronic device cooling architectures. To observe the impact of thermal properties on thin film PCM melting, various PCMs including paraffin, sorbitol, acetamide, and eicosane will be observed. With this experiment, means of enhancing conduction modes within the thin film will be examined. Without formation of convection currents the PCM material distribution should remain constant, allowing increased conduction pathways to be maintained and effectively used over multiple heating and cooling cycles.