Ripken ab , Jeffery A. E-mail: s. Specifically, distortion of the fluid due to the protrusion and the location of the bubbles can affect transport phenomena, and, in turn, the chemical conversion.
Therefore, understanding nucleation and growth of bubbles within microreactors is desirable to optimize reactor performance. A promising approach to that end, and to ultimately control transport phenomena in multiphase catalytic microreactors, is to direct the nucleation of bubbles. For this purpose, we report here a microfluidic device that contains hydrophobic micropits along the smooth floor of a rectangular cross-section microchannel, which were patterned in a silicon substrate using deep reactive ion etching.
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The pits are intended to act as nucleation sites. Device performance was evaluated for the two cases of boiling of water and outgassing of dissolved carbon dioxide CO 2. As intended, bubbles were observed to form at the micropits, but also along the rough microchannel side walls.
The experimentally determined bubble geometry was used as the boundary condition for a 3D-numerical model. Numerical simulations indicated that the presence of bubbles had a large impact on the local flow distribution, concentration field and reaction conversion within the microreactor, and therefore on the overall conversion for a chosen model reaction. They could more easily be released from the surface by fluid shear forces, promising to both reduce the coverage and enhance the conversion at the catalytic surface.
An improved understanding of the contact angle and location of the bubbles, as well as the bubble departure radius and time, is therefore desirable to ultimately control transport phenomena in multiphase systems such as APR reaction mixtures. Bubble contact angles can be altered by electric field gradients, an effect that is utilized in electrowetting-on-dielectrics EWOD applications, 27,28 by micro- or nanoscale surface roughness elements, 29β34 by changing the wall interfacial tension, 35 or by combining the two latter approaches.
