FLOW CONTROL APPARATUS AND METHOD FOR FUEL CELL FLOW FIELDS

An adjustable flow field and flow regulation method for an electrochemical device such as a fuel cell is described. The flow field preferably includes a plurality of flow paths between an inlet and an outlet and a plurality of microvalves for regulating fluid flow through the flow paths in response to changes in the operating states of the fuel cell, such as changes in power output or temperature. For example, adjustment of the microvalves may restrict the number of flow paths through which fluid is flowing to alter the effective active area and current density of the flow field. The valves may be selectively opened or closed, either entirely or partially, to maintain a minimum pressure drop between the inlet and outlet. Alternatively or additionally, adjustment of the valves may alter the direction of fluid flow through at least some of the flow paths. The invention improves the stability of the fuel cell in low power and low reactant stoichiometry operating states without significantly increasing the complexity of the system or increasing parasitic loads. For example, the invention may improve water management in low power modes and avoid related performance problems such as low current density failures and voltage oscillations. The invention may also help reduce the cost and complexity of the system power electronics. L'invention concerne un champ d'Ecoulement rEglable et un procEdE de rEgulation d'Ecoulement pour dispositif Electrochimique du type cellule Electrochimique. Le champ d'Ecoulement comporte de prEfErence une pluralitE de chemins d'Ecoulement entre une entrEe et une sortie et une pluralitE de microvalves pour rEguler l'Ecoulement de fluide A travers les chemins d'Ecoulement en rEaction aux changements d'Etats de fonctionnement de la cellule Electrochimique, comme des changements de sortie de puissance ou de tempErature. Par exemple, le rEglage des microvalves peut limiter le nombre de chemins d'Ecoulement A travers lesquels s'Ecoule le fluide pour modifier la zone active efficace et la densitE de courant du champ d'Ecoulement. Les valves peuvent Etre ouvertes ou fermEes de maniEre sElective, entiErement ou partiellement, pour maintenir une chute de pression minimale entre l'entrEe et la sortie. Autre possibilitE ou possibilitE supplEmentaire, le rEglage des valves peut modifier le sens d'Ecoulement de fluide A travers au moins une partie des chemins d'Ecoulement. L'invention amEliore la stabilitE de la cellule Electrochimique dans des Etats