A multistage system has been proposed for cooling a circulating fluid that is subject to intermittent intense heating. The system would be both flexible and redundant in that it could operate in a basic passive mode, either sequentially or simultaneously with operation of a first, active cooling subsystem, and either sequentially or simultaneously with a second cooling subsystem that could be active, passive, or a combination of both. This flexibility and redundancy, in combination with the passive nature of at least one of the modes of operation, would make the system more reliable, relative to a conventional cooling system.

This Cross Section Is Greatly Simplified to show only selected major features of a heat exchanger according to the proposal.
The system would include a tube-in-shell heat exchanger, within which the space between the tubes would be filled with a phase-change material (PCM). The circulating hot fluid would flow along the tubes in the heat exchanger. In the basic passive mode of operation, heat would be conducted from the hot fluid into the PCM, wherein the heat would be stored temporarily by virtue of the phase change.

Of course, it would become necessary to remove heat from the PCM to maintain or restore its heat-absorption capacity. This would be accomplished by means of the first, active cooling subsystem, which would circulate a cooling fluid through one or more tube(s) in thermal contact with the PCM. For example, such a cooling tube could be wrapped in a spiral around the heat exchanger shell as shown in the figure.

The heat exchanger would include an inner core that would accommodate the second cooling subsystem. As mentioned above, the second cooling subsystem could be active, passive, or both. This subsystem would remove heat from the core by means of heat pipes, a water membrane evaporator, and/or one or more active refrigeration devices. In the case of a water membrane evaporator, heat would be dissipated in the environment by releasing the steam generated at the membrane.

This work was done by David E. Blanding and David I. Bass of the Boeing Co. for Johnson Space Center. For further information, contact the Johnson Innovative Partnerships Office at (281) 483-3809. MSC-23652

NASA Tech Briefs Magazine

This article first appeared in the August, 2005 issue of NASA Tech Briefs Magazine.

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