Scaling and super-cooling in heat storage harvesting devices

Aircraft sensors are typically cable powered, imposing a significant weight overhead. The exploitation of temperature variations during flight by a phase change material (PCM) based heat storage thermoelectric energy harvester, as an alternative power source in aeronautical applications, has recently been flight tested. In this work, the applicability of this technology to use cases with smaller and larger size specifications is studied by fabrication, testing and analysis of a scaled-down and a scaled-up prototype. Output energy of 4.1 J/g of PCM from a typical flight cycle is demonstrated for the scaled-down device, and 2.3 J/g of PCM for the scaled-up device. The higher energy density of the scaled down prototypes is attributed to the reduction in temperature inhomogeneity inside the PCM. The impact of super-cooling on performance is analyzed by employing a simulation model extended to include super-cooling effects. It is found that super-cooling may be beneficial for scaling down, in applications with slow temperature fluctuations.