Patent ID: 7556874

Claim:
In a stack of fuel cells, wherein adjacent cells are separated by a porous, hydrophobic barrier layer having a water intrusion pressure that prevents liquid water from crossing between cells through the barrier layer under normal operating conditions, the cell on one side of the barrier layer defining a flow channel for liquid water adjacent that one side of the barrier layer, the cell on the other side of the barrier layer defining a flow channel for steam adjacent that other side of the barrier layer, said water and steam flow channels being in vapor communication with each other through the barrier layer, the process of cooling the fuel cells by evaporative cooling during fuel cell operation comprising the steps of: flowing liquid water into and through the water flow channel and out of the fuel cell, the water being heated within the water channel by heat produced by the fuel cell; and causing the liquid water to boil as it flows through the water channel by reducing the pressure in the steam channel below the vapor pressure of the flowing liquid water to convert at least some of the water to steam that passes through the barrier layer into the steam channel, wherein the pressure in the steam channel is increased or decreased during cell operation in response to the operating temperature of the cell to increase or decrease the operating temperature of the cell to achieve a desired cell operating temperature; wherein the step of reducing the pressure in the steam channel includes drawing a vacuum in the steam channel, and the step of increasing or decreasing the pressure in the steam channel includes passing the steam through a radiator after the steam leaves the cell and controlling the amount of heat removed from the steam within the radiator; and condensing the steam outside the fuel cell and recirculating a portion of the condensed steam back to the flowing liquid water, wherein the steam originated as the flowing liquid water converted into steam and passed through the barrier layer into the steam channel.