The present invention provides a method and apparatus for the humidification of gas streams, such as reactant gas streams for fuel cells, wherein the specific water evaporation rate, gas delivery temperature, and degree of gas humidity may be adjusted and maintained at predetermined levels. The humidification apparatus is well suited for use in testing the operation of a fuel cell under various well-controlled conditions in order to evaluate the performance of the fuel cell. The amount of water vapor being introduced into the gas stream can be varied up to the saturation point of the reactant gas stream. As the water vapor leaves the evaporation chamber, it mixes with the gas stream in a gas humidification chamber or riser. The gas riser preferably has a baffle disposed therein to attract any water that may have condensed in the gas stream and direct the condensed liquid water toward the evaporation chamber so the water may be evaporated once again. The humidified reactant gas stream is then maintained at a set point temperature which is at least above the dew point temperature of the humidified reactant gas.

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