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Evaporative cooling of fuel cells employing antifreeze solution

Evaporative cooling of fuel cells employing antifreeze solution description/claims

This invention relates to circulating an antifreeze solution from a reservoir through water channels of porous, hydrophilic water transport plates and back to the reservoir; the mixture enters the fine pores of the water transport plates which are warmed by the heat of the fuel cell process, thereby evaporating water which may include product water (but not antifreeze) from the plates into the process oxidant flow channels, cooling the fuel cells. Water is condensed out of the process air oxidant exhaust and returned to re-mix with the concentrated antifreeze.

It is known that water produced at the cathodes of fuel cells has to be removed from the cathodes in order to prevent the water from blocking the flow of oxidant gas, such as air, from reaching the electrodes. It is also known that fuel cells, when operating, must be cooled to keep the fuel cells at a proper operating temperature. Some fuel cells are cooled only by conduction of heat into cooler plates which are interspersed between some or all of the fuel cells.

One known type of fuel cells employ reactant gas flow field plates which are porous and hydrophilic, having fine pores to allow water to pass from the cathode into the oxidant reactant gas flow channels, and to allow water to pass from the fuel reactant gas flow channels toward the membrane. These are typically called water transport plates. Cooling is typically accomplished by sensible heat transfer to water in the water flow channels formed in or adjacent to the water transport plates.

It has been known to cool fuel cells by evaporation, typically by providing atomized water to the reactant gas streams, which water evaporates, thereby cooling the stack.

In fuel cells which have employed separate cooler plates, the use of an antifreeze mixture as coolant in place of water is known. The use of separate cooler plates requires a fuel cell stack to occupy a larger volume than it would without cooler plates. Similarly, atomizing water into reactant gas streams for evaporative cooling requires additional equipment, which increases cost and volume and presents difficulty, especially at shut down, for fuel cell power plants operating in freezing environments.

In any of the cases referred to, even when antifreeze is used in cooler plates, the requirement to eliminate all water from the stack and auxiliary plumbing before freezing, or to otherwise accommodate the likelihood of freezing temperatures during fuel cell power plant shut down poses additional difficulties, requiring apparatus that adds cost and volume, which are most undesirable when a fuel cell is used as a power source for an electric vehicle.

Objects of the invention include: reducing the volume of a fuel cell power plant; eliminating or reducing freezable water in a fuel cell power plant system; improving fuel cell power plant for use where freezing temperatures may be encountered when the fuel cell is not operating; avoiding having freezable liquid in contact with moving parts in a fuel cell power plant; shortening fuel cell power plant startup time by reducing cell stack thermal mass; and improved fuel cell power plant.

According to the invention, fuel cells in a fuel cell power plant are evaporatively cooled by evaporation of at least some of the water in an antifreeze mixture with a freeze depressing substance in the porous, hydrophilic reactant gas flow field plates, which typically have reactant gas flow channels extending from a surface of reactant flow field plates opposite from coolant passageways. The antifreeze coolant mixture circulates through the coolant passageways in or adjacent the reactant gas flow field plates. A more concentrated mixture returns to a coolant reservoir. The evaporation of water from the antifreeze mixture and product water into the reactant streams (primarily the cathode) cools the fuel cell stack. At least some water vapor is condensed out of at least the oxidant reactant gas stream exiting from the stack, the condensed water being returned to the mixture in the accumulator. To avoid diluting the antifreeze mixture, less than all of the water vapor in the air exhaust may be condensed. The rate of condensing may be controlled using a condensate controller to ensure proper water balance, such as a variable flow cooling fan for the condenser, or by cooling the air in the condenser with a controlled circulation of antifreeze.

A pump is used to pump the antifreeze mixture in a conventional fashion similar to the manner of circulating coolant water in conventional fuel cells. Since only the antifreeze is present in the pump, freezing during shutdown is not a problem.

Other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.

FIG. 1 is a block illustration of the invention.

FIG. 2 is a partial perspective view of an embodiment of the invention.

FIG. 3 is a fragmentary view of a variation of FIG. 1.

FIG. 4 is a fragmentary view of an alternative to the embodiment of FIG. 2.

FIG. 5 is a sectioned, side elevation view, with sectioning lines omitted for clarity, of portions of fuel cells useful with the invention.

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• Utility Patent

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