Abstract
The gas/liquid phase separation of CO2 from a water-methanol solution at the anode side of a µDirect-Methanol-Fuel-Cell (µDMFC) plays a key role in the overall performance of fuel cells. This point is of particular importance if the µDMFC is based on a “Lab-on-a-Chip” design with transient working behaviour, as well as with a recycling and a recovery system for unused fuel. By integrating a membrane-based micro contactor downstream into the µDMFC, the efficient removal of CO2 from a water-methanol solution is possible. In this work, a systematic study of the separation process regarding gas permeability with and without two-phase flow is presented. By considering the µDMFC working behaviour, an improvement of the overall separation performance is pursued. In general, the gas/liquid phase separation is achieved by (1) using a combination of the pressure gradient as a driving force, and (2) capillary forces in the pores of the membrane acting as a transport barrier depending on the nature of it (hydrophilic/hydrophobic). Additionally, the separation efficiency, pressure gradient, orientation, liquid loss, and active membrane area for different feed inlet temperatures and methanol concentrations are investigated to obtain an insight into the separation process at transient working conditions of the µDMFC.
Highlights
In recent years, the operating time and the miniaturisation of portable electronic devices such as smartphones, laptops, and many others devices has become a field of high importance
By combining membrane- and micro-engineering -technology, an orientation-independent removal and recovery of carbon dioxide and water from the two-phase flow is possible [9,10,11,12]. This can be achieved by using a porous membrane-based micro contactor installed downstream of the μDMFC with additional integration on the bipolar plates to achieve a compact and flat LOC design including a recycling system
Porous Membranes Based on theoretical considerations (Equations (1) and (2)), only hydrophobic membranes for Based on theoretical considerations (Equations (1) and (2)), only hydrophobic membranes for gas/liquid phase separation were chosen as a separation membrane in a micro contactor
Summary
The operating time and the miniaturisation of portable electronic devices such as smartphones, laptops, and many others devices has become a field of high importance. Two-phase flows are formed by the produced carbon dioxide and water at both -anode and cathode- side This occurring two-phase flow, on the one hand, decreases the accessibility of methanol and oxygen to the catalyst layer on the respective electrode area inside the μDMFC, leading, on the other hand, to a channel blocking phenomena in one or more channels during operation. By combining membrane- and micro-engineering -technology, an orientation-independent removal and recovery of carbon dioxide and water from the two-phase flow is possible [9,10,11,12] This can be achieved by using a porous membrane-based micro contactor installed downstream of the μDMFC with additional integration on the bipolar plates to achieve a compact and flat LOC design including a recycling system. A membrane-based micro contactor for the gas/liquid phase separation with its corresponding systematic study of the gas permeability, influence of the diffusion fluxes, and separation performance at single and two-phase flow conditions, is presented for four different membranes
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