Test Results of Reflux and Phase Change Energy Storage Electronics Cooler

An electronics cooler using reflux heat rejection and phase change material (PCM) energy storage has been built and tested. The cooler provides thermal control for an electromechanical actuator motor drive. These aircraft actuator motor drives do not have an available high performance heat sink, and thus must rely on the quiescent air in an actuator bay or the aircraft structure, as heat sinks. Thermal loads on the power electronics of these motor drives can be quite high for short durations, suggesting the use of phase change energy storage to store the heat until it can be rejected to the available heat sinks. The present experiment used Fluorinert®¹ compound FC72®² for the refluxing fluid, and Shellwax®³ paraffin wax with either a 51° C or 61° C melt temperature as a PCM for high power transients. Critical heat flux was not detected in the present test series, although the peak fluxes at the base of the power die and at the boiler surface were 80 and 20 W/cm², respectively, with a boiler wall superheat of 16K. The motor drive peak heat load of 1,000 W was applied for up to ten minute intervals. For transient loads with a duration of less than six minutes, the reflux/PCM cooler provided a significant performance benefit relative to the baseline air-only cooler.