A concept for a unique zero-g condensing heat exchanger that has an integral ozone-generating capacity has been conceived. This design will contribute to the control of metabolic water vapor in the air, and also provide disinfection of the resultant condensate, and the disinfection of the air stream that flows through the condensing heat exchanger.

Life support for astronauts includes the treatment and revitalization of the air that they breathe. Part of the revitalization is the removal of the excess water vapor from the air. The condensation of water in zero gravity, and its separation from the remaining gaseous phase while in a zero gravity environment, is technically challenging. In addition to the condensing and gas/liquid separation problem, there is the problem of biological fouling of the condensing/separation mechanism due to deposition and subsequent growth of microorganisms on the condensing surface. Not only does this potentially reduce the effectiveness of the condenser/separator, but also represents a contamination point for the astronauts’ water system.

To solve these problems, a combination of a hydrophilic membrane condensing/separating surface, together with an in situ electrochemical generation of ozone at the condenser surface, is proposed. The hydrophilic membrane would be cooled below the ambient dew point by an external coolant source. The moisture-laden ambient air that impacts the membrane surface would condense water on the surface of the membrane. This water would be soaked up and transported through the hydrophilic membrane into the water line, leaving the condensing heat exchanger. During this process, an electrochemical ozone generator located on the air side of the hydrophilic membrane would create a local concentration of ozone in the condensed water, thereby disinfecting it. Excess ozone not absorbed by the water would be exhausted into the air stream where it would contribute to the disinfection and purification of the air stream.

The anode and cathode are made of stainless steel, and between the anode and cathode is a solid electrolyte made of a plastic polymer based on perfluorinated sulphonic acids. The solid electrolyte serves as a thin ion-exchange membrane that is coated on the cathode side with a layer of a mixture of 85% by weight carbon powder and 15% by weight platinum powder. The anode side of the membrane is coated with PbO2 powder. A solution of oxygen-saturated water is fed into the cell, and ozone is produced in the solution on the anode side of the solid electrolyte ion-exchange membrane while water is formed on the cathode side. The H+ that is produced on the anode side by the decomposition of water to form oxygen and ozone migrates through the ion-exchange membrane and reacts with oxygen in the water on the cathode side to form water. The evolution of harmful hydrogen at the cathode is thereby suppressed.

This work was done by Kenneth A. Burke of Glenn Research Center. NASA Glenn Research Center seeks to transfer mission technology to benefit U.S. industry. NASA invites inquiries on licensing or collaborating on this technology for commercial applications. For more information, please contact NASA Glenn Research Center’s technology transfer program at This email address is being protected from spambots. You need JavaScript enabled to view it. or visit us on the Web at https://technology.grc.nasa.gov . Refer to LEW-17825-1.

NASA Tech Briefs Magazine

This article first appeared in the February, 2015 issue of NASA Tech Briefs Magazine.

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