NOVELTY - A humidifier (10) for transferring water vapor from a first gas stream to a second gas stream, comprises plates arranged in a stack, each of the plates defining a gas flow passage for either the first gas stream or the second gas stream, where each of the plates comprises a top, a bottom and a thickness, an inlet opening, an outlet opening, a flow field, an inlet passage connecting the inlet opening to the open top and the open bottom of the flow field, an outlet passage, a planar top sealing surface, a planar bottom sealing surface, and support structures.    USE - The humidifier is used for transferring water vapor from a first gas stream to a second gas stream (claimed).    ADVANTAGE - The fuel cell humidifier has improved structure and is made in an effective and cost-efficient manner.    DETAILED DESCRIPTION - A humidifier (10) for transferring water vapor from a first gas stream to a second gas stream, comprises (a) plates arranged in a stack, each of the plates defining a gas flow passage for either the first gas stream or the second gas stream, where each of the plates comprises: (i) a top, a bottom and a thickness measured between the top and bottom; (ii) an inlet opening along an edge of the plate; (iii) an outlet opening along an edge of the plate; (iv) a flow field defined in a central portion of the plate, the flow field having an open top along the top of the plate and an open bottom along the bottom of the plate; (v) an inlet passage connecting the inlet opening to the open top and the open bottom of the flow field; (vi) an outlet passage connecting the open top and the open bottom of the flow field to the outlet opening; (vii) a planar top sealing surface extending along the top of the plate, where the top sealing surface extends continuously around the flow field, and includes bridging portions extending across the inlet passage and the outlet passage; (viii) a planar bottom sealing surface extending along the bottom of the plate, where the bottom sealing surface extends continuously around the flow field, and includes bridging portions extending across the inlet passage and the outlet passage; (ix) support structures located within the flow field and extending between the top and bottom of the plate; where pairs of the plates are sealed together in the stack with the top sealing surface of one plate sealed to the bottom sealing surface of an adjacent plate; (b) water permeable membranes, where one of the membrane is provided between each pair of adjacent plates in the stack, and is sealed to the pair of adjacent plates, and where the support structures provide support for the water permeable membranes within the flow fields; and (c) an inlet manifold and an outlet manifold for the first gas stream, and an inlet manifold and an outlet manifold for the second gas stream, where the inlet manifold and the outlet manifold for the first gas stream are in flow communication with a first the plates defining the gas flow passages for the first gas stream, and where the inlet manifold and the outlet manifold for the second gas stream are in flow communication with a second the plates defining the gas flow passages for the second gas stream, where the plates are stacked and the manifolds are arranged such that the gas flow passages for the first gas stream alternate with the gas flow passages for the second gas stream throughout the stack, and such that each of the water permeable membranes separates one of the gas flow passages for the first gas stream from one of the gas flow passages for the second gas stream; and where the top and bottom sealing surfaces of the plates, including the bridging portions, are provided with a compressible sealing material. An INDEPENDENT CLAIM is a plate for a humidifier for transferring water vapor from a first gas stream to a second gas stream, the plate comprising: (i) a top, a bottom and a thickness measured between the top and bottom; (ii) an inlet opening along an edge of the plate; (iii) an outlet opening along an edge of the plate; (iv) a flow field defined in a central portion of the plate, the flow field having an open top along the top of the plate and an open bottom along the bottom of the plate; (v) an inlet passage connecting the inlet opening to the open top and the open bottom of the flow field; (vi) an outlet passage connecting the open top and the open bottom of the flow field to the outlet opening; (vii) a planar top sealing surface extending along the top of the plate, where the top sealing surface extends continuously around the flow field, and includes bridging portions extending across the inlet passage and the outlet passage; (viii) a planar bottom sealing surface extending along the bottom of the plate, where the bottom sealing surface extends continuously around the flow field, and includes bridging portions extending across the inlet passage and the outlet passage; and (ix) support structures located within the flow field and extending between the top and bottom of the plate; and where the top and bottom sealing surfaces of the plates, including the bridging portions, are provided with a compressible sealing material.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic, perspective view of a humidifier.    Humidifier (10)    Core (12)    Bolt (66)    Nut (67)    End plate (72)    Manifolds (74, 76, 78, 80)