Prof. Santiago MadrugaSchool of Aeronautics and Aerospace Engineering, Universidad Politécnica de Madrid, Spain
Speech Title: Enhanced Phase Change Materials for Thermoregulation and Waste Energy Recovery
Abstract: The Phase Change Materials (PCM) take advantage of the latent heat of the solid/liquid transition to store large amounts of thermal energy during melting or release it to the environment during solidification, barely changing their temperature. This thermal stability and storage capability makes these materials more compact and efficient than materials that use sensible heat for energy storage and thermoregulation [1,2].
A significant issue in thermal regulation and energy storage with PCM is their low conductivity. This leads to very long times during the heat storage and discharge phases, reducing their usability and performance. We present three mechanisms to enhance the heat transfer rate suitable for engineering applications. First, we show how the thermocapillary effects are a very efficient mechanism to develop convective heat transfer in microgravity and strongly enhance the performance of PCM based systems, without increasing their mass and volume [3,4]. Second, we use dispersed metallic nanoparticles in PCM to enhance the heat transfer rate, and present an empirical model able to predict the performance of nano-enhanced PCM realistically in a wide range of nanoparticle concentrations, sizes, and types . Third, we show how metallic open foams are can be used in addition to convective heat transport to enhance the heat transfer rate robustly.
Finally, we present how to leverage those enhancing heat transfer mechanisms to improve current PCM designs of micro-energy harvesters. The motivation comes from the need to power low consume electronics; such as wireless sensors to monitor environmental variables, industrial processes, health parameters, etc., in places where conventional batteries are impractical. Among the different technologies aimed at power low consume sensors - as solar cells, piezoelectric devices, electrostatic methods, etc.- thermoelectric energy harvesting is one of the best solutions to create autonomous monitoring sensors. Efficient TEGs require a substantial temperature difference across the device structure. This has restricted their use to applications where a hot metal surface is available . We show how coupling thermoelectric generators with PCMs in micro-energy harvesters can increase the electric energy output an order of magnitude with respect to conventional designs. In particular, we pay special attention to designs of autonomous micro-harvesters to power sensors for structural health monitoring systems in aircraft, monitoring in spacecraft, as well as humidity and temperature in soils.
Keywords: Phase Change Materials, nanoparticles, thermoelectric generators, micro-energy harvesting