On the anode side of a DMFC CO2-bubbles emerge. Given hydrophobic channel walls, these bubbles stick to the walls and keep growing such that a strong displacement effect on the water-methanol-flow toward the GDL arises. Hence, cell power increases while the bubble is present. This effect has been numerically predicted by [1] and has been experimentally proven recently by ZBT scientists [2].
Based on those findings the question raised whether the cell power could be permanently increased by adding some kind of artificial bubbles that would lead to a similar displacement effect on the flow at the anode side of a DMFC. Further investigations using laser-optical flow measurement techniques and time-resolved cell-power measurements have been conducted with a special designed single-channel DMFC. Within this special DMFC artificial obstacles are fixed at the anode channel wall opposite to the GDL surface resembling a stationary CO2-bubble sticking to the channel wall. Those obstacles lead to a significant reduction of the channel cross section and create the desired displacement effect on the flow. Results showed an increase of up to 15%- 19% of the cell power with respect to the obstacle-free channel configuration. Power increase tends to scale with blockage ratio. Further investigations are currently under way.
The findings have been presented at the “Fuel Cells 2014 Science & Technology – A Grove Fuel Cell Event” in Amsterdam in April 2014. The poster was awarded best conference poster 2014.
- Department micro systems and fluid mechanics
- ZBT Flow measurements[1] Hutzenlaub, T, Paust, N, Zengerle, R, Ziegler, C: The effect of wetting properties on bubble dynamics and fuel distribution in the flow field of direct methanol fuel cells, Journal of Power Sources, 196: 8048– 8056, 2011
[2] Burgmann, S, Blank, M, Panchenko, O, Wartmann, J: µPIV measurements of two-phase flows of an operated direct methanol fuel cell, Exp Fluids, 54:1513, 2013
