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A WVT unit for a fuel cell system that employs a spiral-wound design to reduce its size and increase its performance. The WVT unit includes a center tube having a plurality of openings through which the cathode exhaust gas flows. The WVT unit also includes a cylindrical portion wound around the cent

A WVT unit for a fuel cell system that employs a spiral-wound design to reduce its size and increase its performance. The WVT unit includes a center tube having a plurality of openings through which the cathode exhaust gas flows. The WVT unit also includes a cylindrical portion wound around the center tube that includes a plurality of enclosures and a plurality of dry spacer layers separating the enclosures. Each enclosure includes a pair of membranes separated by a wet spacer layer. The dry cathode inlet air flows down the dry spacer layers between the enclosures and the cathode exhaust gas flows into the plurality of enclosures through the openings in the center tube along the wet spacer layers to allow the membranes to absorb humidification that is transferred to the cathode inlet air.

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What is claimed is: 1. A fuel cell system comprising: a fuel cell stack receiving a cathode inlet airflow and outputting a cathode exhaust gas flow; a compressor for providing the cathode airflow to the fuel cell stack; and a spiral-wound water vapor transfer unit receiving the cathode airflow from

What is claimed is: 1. A fuel cell system comprising: a fuel cell stack receiving a cathode inlet airflow and outputting a cathode exhaust gas flow; a compressor for providing the cathode airflow to the fuel cell stack; and a spiral-wound water vapor transfer unit receiving the cathode airflow from the compressor and a source of humidification, said water vapor transfer unit including a cylindrical portion having a plurality of enclosures that receive the humidification to humidify the cathode airflow. 2. The system according to claim 1 wherein the plurality of enclosures include opposing membranes that seal a wet spacer layer therebetween, where the humidification flows through the wet spacer layer. 3. The system according to claim 2 wherein the cylindrical portion includes a plurality of dry spacer layers that separate the enclosures, and wherein the humidity from the humidification source flowing through the wet spacer layers is transferred to the cathode airflow flowing through the dry spacers by the membranes. 4. The system according to claim 1 wherein the water vapor transfer unit further includes a center tube around which the plurality of enclosures are wound, said center tube including a plurality of perforations that allow the humidification to enter the plurality of enclosures. 5. The system according to claim 4 further comprising a valve positioned with the center tube, said valve being opened to allow the humidification to flow directly through the center tube and being closed to allow the humidification to flow into the plurality of enclosures through the plurality of perforations. 6. The system according to claim 4 wherein in the center tube has a diameter of about 38 mm. 7. The system according to claim 1 wherein the cathode exhaust gas is the source of humidification. 8. The system according to claim 7 wherein the cathode inlet airflow and the cathode exhaust gas flow flows through the water evaporation transfer unit in a counter-propagating direction. 9. The system according to claim 1 wherein the cylindrical portion is about 12 inches long and has a diameter of about 6 inches. 10. The system according to claim 2 wherein the membranes are hydrophilic membranes. 11. The system according to claim 1 wherein the water vapor transfer unit includes eighty or more enclosures. 12. The system according to claim 1 wherein the plurality of enclosures are formed by folded or pleated layers. 13. A fuel cell system comprising: a fuel cell stack receiving a cathode inlet airflow and outputting a cathode exhaust gas flow; a compressor for providing the cathode airflow to the fuel cell stack; and a spiral-wound water vapor transfer unit receiving the cathode airflow from the compressor and the cathode exhaust gas flow where the cathode exhaust gas flow provides humidity for humidifying the cathode inlet airflow, said water vapor transfer unit including a center tube through which the cathode exhaust gas flows, said center tube including a plurality of openings, said water vapor transfer unit further including a cylindrical portion wound around the center tube and including a plurality of enclosures and a plurality of dry spacer layers separating the enclosures, each enclosure including a pair of membranes separated by a wet spacer layer, wherein the cathode inlet air flows into an end of the cylindrical portion between the plurality of enclosures down the dry spacer layers and the cathode exhaust gas flows into the plurality of enclosures through the openings in the center tube along the wet spacer layers to allow the membranes to absorb humidification that is transferred to the cathode inlet. 14. The system according to claim 13 further comprising a valve positioned within the center tube, said valve being opened to allow the cathode exhaust gas to flow directly through the center tube and being closed to allow the cathode exhaust gas to flow into the plurality of enclosures through the plurality of perforations. 15. The system according to claim 13 wherein in the center tube has a diameter of about 38 mm. 16. The system according to claim 13 wherein the cathode inlet airflow and the cathode exhaust gas flow flows through the water evaporation transfer unit in a counter-propagating direction. 17. The system according to claim 13 wherein the cylindrical portion is about 12 inches long and has a diameter of about 6 inches. 18. The system according to claim 13 wherein the membranes are hydrophilic membranes. 19. A water vapor transfer unit comprising: a center tube having a first end and a second end, said center tube further including a plurality of perforations, said center tube receiving a wet flow at the first end that flows down the center tube and out of the second end; a cylindrical portion wound around the center tube and including a plurality of enclosures and a plurality of dry spacer layers separating the enclosures, each enclosure including a pair of membranes separated by a wet spacer layer, wherein a dry gas flows into an end of the cylindrical portion and flows down the cylindrical portion through the dry spacer layers between the enclosures, and wherein the wet gas flows into the plurality of enclosures through the perforations in the center tube along the wet spacer layers to allow the membranes to absorb humidification that is transferred to the dry flow; and a valve positioned within the center tube, said valve being opened to allow the wet flow to flow directly through the center tube and being closed to allow the wet flow to flow into the plurality of enclosures through the plurality of perforations. 20. The unit according to claim 19 wherein the dry flow and the wet flow through the water evaporation transfer unit in a counter-propagating direction. 21. The unit according to claim 19 wherein the membranes are hydrophilic membranes.