An improved automated system for transferring liquid helium from a supply tank to an end-use cryostat has been proposed. Like automated systems developed previously for the same purpose, this system would reduce the time that must be spent by technicians in replenishing cryostats in equipment required to operate for times longer than cryostat holding times. However, relative to prior automated liquid-helium-transfer systems, this system would operate in a more nearly optimum manner so as to reduce the consumption of liquid helium. Examples of equipment with which this system could be used include apparatuses for long-duration scientific experiments and large cooled electromagnets in medical imaging systems

The system would control the flow of liquid helium through a transfer line and would control ancillary flows of helium gas generated by vaporization of the liquid helium. It would precool the transfer line, as needed, to to minimize boiling of liquid helium in the line and would prevent the flow of warm gas into the cryostat.

The system would include a liquid-level sensor in the cryostat, an electronic control circuit, three valves (V1, V2, and V3, as shown in the figure), and a temperature sensor in the transfer line upstream of V1. The transfer line would comprise a stainless steel inner tube for carrying liquid helium, surrounded by a vacuum jacket to minimize loss of heat, surrounded by an outer tube for the passage of helium gas to cool the parts within. V2 would control the flow of liquid helium through the inner tube. V1, located at the top of the inner tube, would control the flow of helium gas fro the inner tube to the outer tube. After flowing through the outer tube, the helium gas could be vented, or, if necessary for safety it could be collected. V3 would be used to stabilize the system by bleeding off helium hag generated by vaporization in the storage tank.

Upon sensing that the cryostat liquid level was below the minimum acceptable level, the system would trigger a regulator to pressurize the storage tank to pump liquid helium into the transfer line. Simultaneously, V1 would be opened. The initial warmth of the transfer line would cause some of the liquid helium to boil; the resulting vapor would flow through V1 into the outer tube. Once the temperature measured just upstream of V1 had fallen to predetermined level near the boiling temperature of helium, V1 would be closed and then V2 would be opened so that liquid helium could flow through the inner tube to the cryostat. When the cryostat liquid level reached the maximum acceptable level, the transfer would be considered to be complete and hence both V1 and V2 would be closed.

This work was done by G. Mark Cushman and Richard M. Gummer of Goddard Space Flight Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

the Patent Counsel
Goddard Space Flight Center; (301) 286-7351.

Refer to GSC-14106

NASA Tech Briefs Magazine

This article first appeared in the October, 2001 issue of NASA Tech Briefs Magazine.

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