Development of a Cold Plate for Spatial and Temporal Temperature Uniformity

Under a NASA SBIR contract, Advanced Cooling Technologies, Inc. (ACT) is developing a Variable Conductance Cold Plate (VCCP) to provide spatial and temporal isothermality over a 0.5 m2 area despite changes in heat load or inlet coolant temperature. In Phase I, ACT designed and demonstrated, through simulation and experiment, a subscale prototype cold plate capable of managing heat fluxes up to 10 W/cm2 while maintaining spatial isothermality to within 2 K and temporal isothermality to less than 0.1 K/min while sink conditions changed by 1 K/min. This behavior results from a passive design that exploits two-phase phenomena and the unique behavior of fluids at saturation conditions. Specifically, the design features a large vapor chamber linked to an actively pumped heat exchanger by Variable Conductance Heat Pipes (VCHP). The VCHP array is responsible for adjusting heat transfer conditions between the vapor chamber and heat exchanger, which serves as the heat sink for the cold plate. This allows the VCCP to maintain vapor chamber temperature while sink conditions change. The vapor chamber, meanwhile, provides an isothermal cold plate surface by exposing any heat sources mounted to this surface to an evaporating working fluid. Missions that could benefit from such temperature control include Low Earth Orbit (LEO) satellites and interplanetary probes that use instrumentation that are sensitive to rapid changes in temperature or temperature non-uniformity between devices. The thermal environments of both types of missions can experience large changes in sink conditions that result from the spacecraft s close proximity to a celestial body, large changes in the spacecraft s distance from the sun throughout the mission, or both. In this paper, discussion focuses on the design and testing of a sub-scale prototype VCCP intended to address these changing conditions, as well as work planned during Phase II of the project.