Bubble Size Distribution and Two-Phase Pressure Drop in Thin-Gap Microchannel
Advancing the chemical engineering fundamentals
Multifase Flows - II (T2-5b)
Keywords: thin-gap microchannel, two-phase flow, flow-patterns, pressure drop
Process intensification in production of fine chemicals can be achieved using various types of microreactors. One of suitable arrangements for electrochemical reactions is a thin-gap microreactor. Thin-gap microreactor can be used as a single-pass flow-through reactor, with electrodes built in front and rear walls. In case of electroorganic oxidation, the desired reaction takes place on anode, whereas on cathode hydrogen is generated from the solvent as a counter reaction. Evolution of gas leads to formation of a two-phase system inside the microreactor.
Bubble presence near the electrode has negative effect on reactor efficiency due to the hindrance of electrode active surface. If the bubble covers large part of electrode (its diameter is much larger than reactor thickness) it blocks electrode surface from the bulk liquid. Only a thin liquid film exists between the bubble and electrode. Mass transfer from the bulk liquid to this film is slow and the electrode area is not fully utilized for the reaction. Therefore, for the efficient reactor design, the understanding of the bubble size distribution and flow patterns is essential.
Another parameter considered in reactor design is the pressure drop. For individual microreactor the pressure drop is not so important because of its low value. However, in the case of reactor stack, pressure drop can play significant role when determining optimal operating condition. Two-phase pressure drop has been intensively studied during last years and several correlations are already available in literature.
Present study experimentally investigates the two-phase flow in a rectangular microchannel. Cross section of the microchannel is 10×0.1 mm, and orientation is vertical. Flow in the thin-gap microchannel is visualized using digital camera for a range of operating conditions. Image processing is than used for the evaluation of bubble size distribution. From these data, basic flow map is formulated. The applicability of previously proposed correlations for two-phase frictional pressure drop to thin-gap channel is investigated. Finally, two-phase pressure drop is identified with flow patterns existing in microreactor.
Presented Monday 17, 15:20 to 15:40, in session Multifase Flows - II (T2-5b).
