New multi-path spiral flow field designs are developed to improve the under-rib convection mass transport, and consequently the performance of direct methanol fuel cells. The new designs are based on the approach of maximizing the number of the flow paths and flow path patterning. Three new designs are proposed, one design with two flow paths and two designs with three flow paths. To assess the effect of the proposed designs on fuel cell
performance, a three-dimensional, isothermal, and single-phase mathematical model for the DMFC is developed and validated using the experimental data available in the literature. Results clearly indicate a significant increase in fuel cell performance with the enhancement of convection mass transport. It is found that fuel cell power increases by 104% and 74% at inlet methanol concentrations of 0.25 M and 0.5 M, respectively, with the
use of convection-enhanced spiral flow fields. Furthermore, comparing the predicted results at 0.25 M and 0.5 M inlet methanol concentrations reveals that the power obtained with the newly developed design at 0.25 M inlet methanol concentration is approximately the same as that obtained using a conventional spiral flow field at 0.5 M inlet methanol concentration. Therefore, the approach of using convection-enhanced flow fields enables a
reduction in the required inlet methanol concentration, which in turn tackles the methanol crossover problem without affecting the output power of the cell. |
