Design, fabrication, and testing of a cryogenic thermal diode

Cryogenic heat pipe diode applications and a new heat pipe geometry are discussed. This new geometry employs excess liquid to block the vapor space of the evaporator and part of the transport section during reverse mode conditions. An orifice plate is positioned in the pipe at the blocking meniscus location, with the opening arranged to permit proper liquid distribution in both ground tests and zero g operation. Experimental data are presented for a room temperature heat pipe modified to operate as a blocking orifice diode. The test results verify feasibility of the blocking orifice technique with the diode having a rapid shutoff characteristic. The selection of a diode for fabrication and test was based mainly on a parametric investigation of the liquid trap and liquid blockage techniques. The blocking orifice form of liquid blockage was selected for the cryogenic diode based on its high throughput, small reservoir requirement, and small energy and time required for shutoff.