Analysis of heat transfer and fluid flow characteristics of a hydrogen reformer for fuel cell applications

Abstract

Fuel cells that utilize hydrogen are promising energy conversion units that have a high intrinsic efficiency. However there are operational difficulties in storing hydrogen. One way to alleviate this problem is to generate hydrogen in situ from a liquid fuel such as ethanol in a reformer. In this paper, an ethanol reformer was modeled as a tubular non-isothermal, non-isobaric packed-bed reactor with an annular heat transfer jacket, operating at unsteady state. Since the reforming reaction is endothermic, it is necessary to design a suitable heat transfer jacket to provide heat to the reformer. The partial differential equations of the reformer model were solved numerically after estimating the model parameters from the literature. The effect of inlet conditions on the heat transfer characteristics were studied. Model predictions of hydrogen generation were compared to experimental data available in the literature for a laboratory-scale reformer and were shown to be in excellent agreement. A commercial-scale reformer was designed using this high-fidelity model that can produce sufficient hydrogen to generate up to 5 kW of power when used in conjunction with a Ballard Mark V fuel-cell stack. Experimental data from the dynamic power consumption in a 3-bedroom house were used to determine the size of the reformer as well as a back-up battery that supplies power when the reformer is unable to meet the power demand.