Abstract: A humidifier comprising a wound portion wrapped around a central axis and comprising enclosures, a first one the enclosures comprising a first pair of semipermeable membranes separated by a first spacer layer to form one among wet-gas channels, and a second one of the enclosures comprising a second pair of semipermeable membranes separated by a second spacer layer to form one among dry-gas channels. The dry-gas channels are configured to receive a dry gas through at least part of a first frontal area of the wound portion and in an axial direction along the dry-gas channels. The wet-gas channels are configured to receive a wet gas through at least part of a second frontal area of the wound portion and in the axial direction along the wet-gas channels, the second frontal area being opposite to the first frontal area.