NOVELTY - A membrane humidifier (10) comprises a wet side plate (12) having flow channels (16) to facilitate a flow of a wet gas; a dry side plate (14) having flow channels (20) to facilitate a flow of a dry gas; a first diffusion medium (24) and a second diffusion medium (26) between the wet side plate and the dry side plate; and a membrane (28) between the first diffusion medium and the second diffusion medium, to permit a transfer of water vapor.    USE - A membrane humidifier used for a fuel cell (claimed).    ADVANTAGE - The membrane humidifier achieves a minimized mass transport resistance and pressure drop.    DETAILED DESCRIPTION - A membrane humidifier (10) comprises:    (A) a wet side plate (12) having flow channels (16) formed on its top side and bottom side, the flow channels facilitate a flow of a wet gas;    (B) a dry side plate (14) having flow channels (20) formed on its top side and bottom, the flow channels facilitate a flow of a dry gas, where the flow channels of the wet side plate create a cross-flow pattern with the flow channels of the dry side plate;    (C) a first diffusion medium (24) between the wet side plate and the dry side plate, to permit a transfer of water vapor;    (D) a second diffusion medium (26) between the wet side plate and the dry side plate, to permit a transfer of water vapor; and    (E) a membrane (28) between the first diffusion medium and the second diffusion medium, to permit a transfer of water vapor, where the first diffusion medium abuts the membrane and the wet side plate, and the second diffusion medium abuts the membrane and the dry side plate, and where water vapor in the wet gas is transferred through the first diffusion medium, the membrane, and the second diffusion medium to the dry gas.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view of a portion of a membrane humidifier.    Membrane humidifier (10)    Wet side plate (12)    Dry side plate (14)    Flow channels (16)    Flow channels (20)    First diffusion medium (24)    Second diffusion medium (26)    Membrane (28)