PEM fuel cell passive water management
View Patent ↗Water flow field inlet manifolds ( 33, 37 ) are disposed at the fuel cell stack ( 11 ) base. Water flow field outlet manifolds ( 34, 38 ) are located at the fuel cell stack top. Outlet and inlet manifolds are interconnected ( 41-43, 47, 49, 50 ) so gas bubbles leaking through the porous water transport plate cause flow by natural convection, with no mechanical water pump. Variation in water level within a standpipe ( 58 ) controls ( 56, 60, 62, 63 ) the temperature or flow of coolant. In another embodiment, the water is not circulated, but gas and excess water are vented from the water outlet manifolds. Water channels ( 70 ) may be vertical. A hydrophobic region ( 80 ) provides gas leakage to ensure bubble pumping of water. An external heat exchanger ( 77 ) maximizes water density differential for convective flow.
1. A PEM fuel cell power plant having passive water management, comprising:
a PEM fuel cell stack comprising plurality of fuel cells, each of said fuel cells having a membrane electrode assembly with a cathode on one side and an anode on the other side, the cathode and anode each comprising a porous flow field plate having reactant gas flow channels on one surface and water flow channels on a surface opposite to said one surface;
at least one water outlet manifold near the top of said fuel cell stack, said water flow channels extending from near the bottom of each of said fuel cells generally upwardly to said at least one water outlet manifold, thereby allowing fuel reactant gas which leaks into paid water flow channels on said anode side to bubble-pump water in said water channels on said anode side upwardly to one said at least one water outlet manifold, and allowing oxidant reactant gas which leaks into said water flow channels on said cathode side to bubble-pump water in said water channels on said cathode side upwardly to one said at least one water outlet manifold;
at least one vent connected to said at least one water outlet manifold to allow venting of fuel and oxidant gas from said fuel cell stack, whereby water management in said fuel cell stack is effected without a mechanical pump;
at least one water inlet manifold disposed at the base of said fuel cell stack, said water channels extending from said at least one water inlet manifold generally upwardly to said at least one water outlet manifold; and
conduits connecting said at least one water inlet manifold with said at least one water outlet manifold, whereby said water flows through said stack by natural convection.
2. A power plant according to claim 1 wherein:
said at least one vent comprises part of a gas separator.
3. A power plant according to claim 1 wherein said conduits include a controllable valve, and further comprising:
means for controlling said controllable valve in response to the level of water in said fuel cell stack, whereby to control the amount of water in said stack.
4. A power plant according to claim 1 further comprising:
a plurality of coolant flow plates interspersed between at least some of said fuel cell, each having coolant flow channels therein;
a coolant flow system in fluid communication with said coolant flow channels, said coolant flow system including a radiator for cooling the coolant and means responsive to the level of water in said fuel cell stack for controlling the cooling of coolant in said coolant flow system.
5. A power plant according to claim 1 further comprising:
a hydrophobic portion on at least one of said porous plates, thereby to ensure gas leakage sufficient to provide adequate bubble-pumping of a water/gas mixture in said water channels of said at least one porous plate.
6. A power plant according to claim 1 further comprising:
a heat exchanger in said conduits thereby providing sufficient differential density between water in said conduits and water in said water channels to ensure convective flow of water/gas mixture in said water flow channels.
7. A power plant according to claim 1 further comprising:
a gas separator connected to at least one of said water outlet manifolds to remove gas from a water/gas mixture flowing in said water channels connected to said at least one water outlet manifold.