Portable micro direct methanol fuel cells (µDMFC) are of great interest as power supply for small electric devices. During the operation, CO2 is formed by the reaction of methanol and water at the anode side of the fuel cell, generating a two-phase flow.
If not separated from the fuel, the CO2 bubbles can reduce the cell’s performance by lining the anode surface. Therefore, a micro contactor for the two phase separation of CO2 from the methanol/water fuel mixture suitable for portable applications is developed.
The separation efficiency of the micro contactor depends on the properties of the porous membrane, the fluid supply into to the micro channel and pressure conditions during the separation. The influence of the channel walls’ wettability on the two-phase flow in combination with different membranes and separation performance was characterised by several means like:
- Contact angle of membranes and channel walls
- Visual investigation of the two-phase flow pattern in a micro channel.
- Experimental determination of the separation efficiency with a micro contactor.
The two-phase flow dynamic with heterogeneous channels distinctly differs from regular homogeneous ones. A dependency of the flow pattern on the membrane’s and channel walls’ wettability (hydrophilic/hydrophobic) is present and influences the separation efficiency. Current results are:
- The more hydrophobic the membrane, the more efficient the gas separation.
- Hydrophilic channel walls enhanced separation performances.
The best separation efficiency was achieved by combining hydrophilic walls with a hydrophobic membrane and controlled pressure conditions during the separation. Complete separation achievable with appropriate pressure conditions and sufficient membrane area.
Future studies will be done with a modular measuring cell with preheating system (micro heat exchanger) and porous membrane or microsieve based micro contactor. Additionally, the pre heating system can be replaced by a µDMFC to study the separation at transient µDMFC operation conditions.