The Hybrid Capillary Pumped Loop

This paper describes the operational principles of a hybrid capillary pumped loop in general, and results on testing of a high power hybrid system in particular. A hybrid capillary pumped loop is a thermal control system which consists of a capillary pumped loop and a mechanical pump which is placed in series with the capillary evaporators in the liquid return line. The hybrid loop can be operated in either a passive capillary mode, or in a pump-assisted mode, whereby the mechanical pump augments the heat transport capability of the capillary evaporators. The high power hybrid system was built to demonstrate the feasibility of such a hybrid loop concept. Test results verified that a hybrid loop could be operated in either mode, and that transition between these two modes of operation required opening or closing a single valve on the liquid line. Heat transport limit of 25 kW in the capillary mode and over 50 kW in the pump-assisted mode were demonstrated, using ammonia as the working fluid. The high power hybrid system retains the simplicity and operational characteristics of a capillary pumped loop while incorporating significant performance latitude afforded by the mechanical pump.