Passive Thermal Management Using Phase Change Materials: Experimental Evaluation of Thermal Resistances

Limited heat dissipation and increasing power consumption in processors has led to a utilization wall. Specifically due to high transistor density, not all processors can be used continuously without exceeding safe operating temperatures. This is more significant in mobile electronic devices which, despite relatively large chip area, are limited by poor heat dissipation — primarily natural convection from the exposed surfaces. In the past, solid-to-liquid phase change materials (PCMs) have been employed for passive thermal control — absorbing energy during the phase change process while maintaining a relatively fixed temperature. However, the lower thermal conductivity of the liquid phase after melting often limits the heat dissipation from the PCM, and in the liquid state, the material can flow away from the desired location. Here we focus on characterization of thermal performance of PCMs with the goal of evaluating dry (gel-to-solid/amorphous-to-crystalline) phase change materials which are intended to mitigate the pumpout issue. Critical thermophysical properties include the thermal conductivity, heat capacity, and latent heat of the phase/state change. The thermal resistance throughout the phase change process is measured by in-house rig which miniaturizes the reference bar method for use with infrared temperature sensing.