Advanced Thermal Metrology for Phase Change Materials

Event Date: November 17, 2015
Authors: Yash Ganatra,Michael Woodworth, and Amy Marconnet
Journal: ASME 2015 International Mechanical Engineering Congress & Exposition
Paper URL: Conference Website
ASME 2015 International Mechanical Engineering Congress & Exposition, Houston, TX, 2015.

Phase change materials (PCMs) are becoming increasingly important in applications ranging from passive thermal management to energy storage. As an example, in thermal management of electronics, phase change can enable locally high heat removal rates at locations of increased temperature enabling cooling of transient hot spots. Traditional PCMs melt upon heating, but a new class of polymeric “dry” phase change materials are of interest as they switch from gels to solid upon heating which should lead to continued high cooling rates after the initial phase change. In electronics applications in particular, many cycles of heating and cooling are expected. The evolution of the thermal conductivity and enthalpy of phase change during repeated cycling is critical to predicating how these materials will perform during realistic heating events. In this work, we characterize the properties of phase change materials using a series of measurements primarily utilizing infrared microscopy for non-contact temperature mapping. First, an infrared microscopy enhanced miniaturized version of the standard reference bar method quantifies the thermal conductivity and total thermal resistance at steady state conditions (e.g. before or completely after phase change has occurred for the entire sample). Our preliminary work with commercial phase change thermal interface materials show the efficacy of our miniaturized IR method [1]. Recently, we measured total thermal resistance of 57 cm2K/W and an intrinsic thermal conductivity of 1.6 W m-1 K-1 for a 2 mm thick pad of Parker Chromerics Thermflow T725 before phase change. As opposed to our past work, here we improved the measurement rig to allow the PCM melt in situ without significant pump out of the molten phase change material. This in turn enables thermal conductivity characterization at the high temperature state, repeated melting-solidification cycles, and direct non-contact observation of the temperature profiles in a well-controlled configuration during melting. Second, real-time infrared microscopy during phase change allows tracking of the temperature gradients and phase change fronts in situations which mimic those seen in electronic devices. Of particular importance is determining whether the phase change material can accommodate rapid spikes in heat flux, as well as long term lower magnitude heat dissipation. Third, differential scanning calorimetry measures the enthalpy of the phase or state change. Finally, combining thee experimental property measurements with finite element models will enable identification of optimum of material properties for maintaining desired operating temperatures. Models will allow exploration of different geometries, heat flux profiles, and guide the development of the new PCMs.

 

[1] Y. Ganatra and A. Marconnet, “Passive Thermal Management using Phase Change Materials”, InterPACK 2015, San Francisco, CA, 2015.