Refueling spacecraft in space offers tremendous benefits for increased payload capacity and reduced launch cost, but the problem of thermal stratification in long-term storage tanks presents a key challenge. To meet this challenge, a reliable, compact, lightweight, and efficient cryogenic mixing pump was developed with no moving parts. The pump uses an innovative thermodynamic process to generate fluid jets to promote fluid mixing. This thermodynamic process eliminates moving parts to generate pumping action. Inherent to its design, the pump is self-priming and can efficiently pump two-phase fluid. The device will significantly enhance the reliability of pressure control systems for storage tanks.

In thermal stratification, vaporized hot spots develop inside the storage chamber, elevating pressure and creating an overpressure hazard. Mechanical mixing to de-stratify the fluid and create a uniform bulk temperature in microgravity is an effective approach for controlling the pressure inside a large propellant tank. Reliable operation at cryogenic temperature is a challenge for pumps because no lubricants can be used. Pumping a saturated cryogenic fluid poses several unique challenges for a mechanical pump. Existing pumps for cryogenic fluid transfer require a high degree of subcooling at the pump inlet to prevent pump cavitation or de-priming.

The thermodynamic process is well known and has been previously used to develop heat pumps and refrigeration devices. This innovation applies this scientific principle to two-phase room-temperature and cryogenic refrigerants to produce pumping from cyclic pressurization and depressurization of the fluid through a thermal process. The thermodynamic process enables efficient use of the heat absorbed during the depressurization step to thermally raise the cryogen pressure during the pressurization step, thus minimizing the net heat input to the cryogen due to the pumping process.

On the pressurization process, the pumping chamber heats the cryogen, increasing pressure within the pump. The increased pressure displaces some of the fluid within the pump.

On the cooling cycle, the pumping chamber cools the cryogen. The vaporized cryogen in the pumping chamber then condenses, creating a suction pressure within the pump that draws in addition fluid. Check valves are used to ensure that the fluid is one-directional for efficient pumping.

This work was done by Weibo Chen and Adam Niblick of Creare Incorporated for Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-19140-1.

NASA Tech Briefs Magazine

This article first appeared in the June, 2014 issue of NASA Tech Briefs Magazine.

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