Abstract
We investigate the absorption of a pure gas into a liquid in laminar flow past a superhydrophobic surface consisting of alternating solid walls and micro-bubbles. We experimentally measure and numerically estimate the dynamic mass transfer of gas absorption at stable gas–liquid interfaces for short contacting times. We study the net rate of gas absorption experimentally by in situ measurements of dissolved oxygen concentration profiles in aqueous solutions flowing over oxygen bubbles by fluorescence lifetime imaging microscopy. We numerically analyze the dynamics of interfacial mass transfer of dissolved oxygen by considering (i) kinetic equilibrium conditions at bubble surfaces that are conventionally described by Henry's Law and (ii) non-equilibrium conditions at bubble surfaces using Statistical Rate Theory (SRT). Our experimental results show that kinetic equilibrium is not established for short contact times. Mass transfer of gas into liquid flow past micro-bubbles can be well described by our simulations performed with the non-equilibrium theory for a short exposure time (∼180 μs) of liquid with a microbubble, deviating from the commonly accepted Henry's Law.
Highlights
Gassing/degassing of liquids is of interest in various research elds and applications ranging from the multiphase chemical reactors to biotechnologies in both the macro- and microscale.[1,2,3] Traditional gas–liquid contacting equipment such as distillation columns, packed towers, tray/plate columns and bubble columns provide direct contact of gas–liquid and phase equilibrium-based absorption/desorption processes at these interfaces
We numerically analyze the dynamics of interfacial mass transfer of dissolved oxygen by considering (i) kinetic equilibrium conditions at bubble surfaces that are conventionally described by Henry's Law and (ii) non-equilibrium conditions at bubble surfaces using Statistical Rate Theory (SRT)
We numerically study the dynamics of interfacial mass transfer of dissolved oxygen in the liquid side microchannel embedded with curved oxygen microbubbles, using two models of interfacial gas concentration at the (i) kinetic equilibrium state and (ii) non-equilibrium state using Statistical Rate Theory (SRT)
Summary
Gassing/degassing of liquids is of interest in various research elds and applications ranging from the multiphase chemical reactors to biotechnologies in both the macro- and microscale.[1,2,3] Traditional gas–liquid contacting equipment such as distillation columns, packed towers, tray/plate columns and bubble columns provide direct contact of gas–liquid and phase equilibrium-based absorption/desorption processes at these interfaces. Besides the conventional gas–liquid contacting equipment, porous hydrophobic membranes in gas–liquid contacts are increasingly utilized because of several advantages, such as their xed interfacial area used for the stabilization of the gas– liquid interfaces.[7,8,9,10] Mass transfer characteristics of gas absorption/desorption in membrane contactors have been widely studied.[7,10,11,12,13,14,15] The overall mass transfer process is reported to consist of four consecutive steps: (i) transport from the bulk gas phase to the outer surface of the membrane, (ii) diffusion through the membrane, (iii) dissolution of gas into liquid, and (iv) liquid phase transport.
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