A humidifier uses a field of hydrophobic, nanotubes (e.g., vertically aligned carbon nanotubes) to humidify a gas. Voids in the field form liquid flow channels that are wide enough for liquid water to pass through. The nanotubes are spaced close enough to each other to prevent the water from escaping the channels. Water in the channels is absorbed by gas that flows and/or diffuses between the nanotubes. Humidity levels in the gas can be measured and controlled to a desired level by controlling the rate of flow of gas through the humidifier, controlling heating of the gas, and/or adjusting the total area of molecular transfer from the water to the gas by providing multiple banks of nanotubes and controlling the number of banks through which the gas flows.
