A thermally coupled metal hydride hydrogen storage and fuel cell system

Abstract

This paper examines the ability of metal hydride storage systems to supply hydrogen to a fuel cell with a time varying demand, when the metal hydride tanks are thermally coupled to the fuel cell. A two-dimensional mathematical model is utilized to compare different heat transfer enhancements and storage tank configurations. The scenario investigated involves two metal hydride tanks containing the alloy Ti 0.98Zr 0.02V 0.43Fe 0.09Cr 0.05Mn 1.5, located in the air exhaust stream of a fuel cell. Three cases are simulated: a base case with no heat transfer enhancements, a case with external fins attached to the outside of the tank, and a case where an annular tank design is used. For the imposed duty cycle, the base case is insufficient to provide the hydrogen demands of the system, while both the finned and annular cases are able to meet the demands. The finned case yields higher pressures and occupies more space, while the annular case yields acceptable pressures and requires less space. Furthermore, the annular metal hydride tank meets the requirements of the fuel cell while providing a more robust and compact hydrogen storage system.