A membrane exchange humidifier employs a water permeable membrane
comprising a microporous polymer and a hydrophilic additive. In operation,
the membrane preferably has favorable water transmission properties and
resists transmission of reactant gas or other components. The membrane is
suitable for use even when permeable in its dry condition to the wet or
dry gases in the humidifier, and/or when the wet and dry gases are of
different composition. By wetting the membrane, the presence of an amount
of liquid water in the wet gas can reduce gas transmission through the
membrane to an acceptable level. The humidifier is useful in fuel cell
systems in which a reactant gas supply stream, such as the oxidant supply
stream, is humidified primarily using water vapor from a fuel cell
reactant exhaust stream. The humidifier is particularly suitable for use
in conjunction with solid polymer fuel cell systems. The improved
mechanical and welding properties of the membrane allow for a simpler
humidifier configuration.
