Liquid metal heat exchanger for high temperature fuel cells

1. A heat exchanger for a fuel cell stack, said heat exchanger comprising:

a first plate;

a second plate;

said first and second plates being connected to one another by at least one wall;

said first and second plates and said at least one wall forming an enclosure having an interior area defined by interior surfaces of said enclosure;

at least one liquid metal disposed within said interior area; and

transfer means disposed within said interior area, said at least one liquid metal being caused to flow within said transfer means and said interior area in response to a temperature gradient applied to said enclosure.

2. The heat exchanger of claim 1 , wherein:

said transfer means comprises at least one porous coating disposed on at least a portion of said interior surfaces;

said porous coating includes a plurality of capillaries therein, wherein at least a portion of said capillaries are connected to one another; and

said at least one liquid metal is transported by capillary action within said capillaries.

3. The heat exchanger of claim 2 , wherein said porous coating comprises a metal.

4. The heat exchanger claim 2 , wherein said porous coating is electrically conductive.

5. The heat exchanger of claim 1 , wherein said porous coating extends between opposing portions of said interior surfaces forming porous bridges therebetween, said porous coating and said porous bridges having exposed surfaces which define at least one cavity within said interior area for accommodating phase changes of said at least one liquid metal.

6. The heat exchanger of claim 1 , wherein said enclosure is electrically conductive.

7. The heat exchanger of claim 1 , wherein said at least one liquid metal comprises at least one of sodium, potassium and a combination sodium and potassium.

8. A fuel cell stack, said fuel cell stack comprising:

a plurality of fuel cells stacked along a common axis, each of said plurality of fuel cells comprising a first conduit disposed adjacent to an anode, a second conduit disposed adjacent to a cathode and an electrolyte disposed between said anode and said cathode;

a heat exchanger disposed between adjacent fuel cells;

said heat exchanger comprising a first plate and a second plate, said first and second plates being connected to one another by at least one wall, said first and second plates and said at least one wall forming an enclosure having an interior area defined by interior surfaces of said enclosure;

at least one liquid metal disposed within said interior area; and

transfer means disposed within said interior area, said at least one liquid metal being caused to flow within said transfer means and said interior area in response to a temperature gradient applied to said enclosure.

9. The fuel cell stack of claim 8 , wherein said heat exchanger includes an extension protruding from said fuel cell stack.

10. The fuel cell stack of claim 9 , wherein said extension discharges heat to an area outside of said fuel cell stack.

11. The fuel cell stack of claim 9 wherein said extension includes at least one heat transfer fin projecting outwardly therefrom.

12. The fuel cell stack of claim 8 , wherein:

said transfer means comprises at least one porous coating disposed on at least a portion of said interior surfaces;

said porous coating includes a plurality of capillaries therein, wherein at least a portion of said capillaries are connected to one another; and

said at least one liquid metal is transported by capillary action within said capillaries.

13. The fuel cell stack of claim 8 , wherein said porous coating extends between opposing portions of said interior surfaces forming porous bridges therebetween, said porous coating and said porous bridges having exposed surfaces which define at least one cavity within said interior area for accommodating phase changes of said at least one liquid metal.

14. A method for operating a fuel cell stack, said method comprising the steps of:

providing a plurality of fuel cells stacked along a common axis, each of said plurality of fuel cells comprising a first conduit disposed adjacent to an anode, a second conduit disposed adjacent to a cathode and an electrolyte disposed between said anode and said cathode;

providing a heat exchanger disposed between adjacent fuel cells, said heat exchanger comprising a first plate and a second plate, said first and second plates being connected to one another by at least one wall, said first and second plates and said at least one wall forming an enclosure having an interior area defined by interior surfaces of said enclosure;

providing at least one porous coating on at least a portion of said interior surfaces and at least one liquid metal disposed in said porous coating;

heating at least one of said fuel cells to at least a boiling point of said liquid metal;

supplying heat from said fuel cells into an evaporation area of said heat exchanger;

transferring at least a portion of said heat from said evaporation area into said liquid metal;

evaporating at least a portion of said liquid metal into a metal vapor;

flowing a coolant over a condensation area of said heat exchanger;

removing at least a portion of said heat from said condensation area;

transporting at least a portion of said metal vapor from said evaporation area to said condensation area;

condensing at least a portion of said metal vapor into said liquid metal in said condensation area; and

transporting said liquid metal to said evaporation area through said porous coating.

15. The method of claim 14 , wherein said coolant is an oxidant which is preheated and supplied to said second conduit.

16. The method of claim 14 , comprising the steps of:

flowing a fuel into said first conduit; and

preheating said fuel for reformation thereof.