A Prototype Capillary Starter Pump Cold Plate

The start-up of a capillary pumped loop under a fully flooded condition is often difficult. The problem is due to the presence of a high superheat at the onset of nucleate boiling, and the associated large pressure spike that results in possible vapor penetration through the wick. To overcome the start-up difficulty, a capillary starter pump has been developed. The starter pump is similar to the traditional evaporator pump except for a bayonet tube that is connected directly from the reservoir to the inside of the pump. Such an evaporator design is selfpriming since all displaced liquid must pass through the pump. The starter pump can replace the traditional capillary pump to provide capillary pumping for heat transport. It can further be integrated into a cold plate to receive heat from distributed sources such as spacecraft instruments. Isothermalization of the cold plate can be accomplished by incorporating heat pipes into the cold plate. A prototype capillary starter pump cold plate was built and subjected to rigorous ground tests. Experimental results showed excellent performance and demonstrated the effectiveness of a starter pump in overcoming start-up difficulties. Such a starter pump cold plate design has been selected for the instrument thermal control system of the Earth Observing System.