Dry microfoams: formation and flow in a confined channel |
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Authors: | J-P Raven P Marmottant F Graner |
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Institution: | (1) Laboratoire de Spectrométrie Physique, CNRS - UMR 5588, Université Grenoble I, B.P. 87, 38402 St Martin d'Hères Cedex, France |
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Abstract: | We present an experimental investigation of the agglomeration of
microbubbles into a 2D microfoam and its flow in a rectangular microchannel. Using a
flow-focusing method, we produce the foam in situ on a
microfluidic chip for a large range of liquid fractions, down to a few percent in liquid.
We can monitor the transition from separated bubbles to the desired
microfoam, in which bubbles are closely packed and separated by thin films.
We find that bubble formation frequency is limited by the liquid flow rate, whatever the gas pressure. The formation frequency
creates a modulation of the foam flow, rapidly damped along the channel. The average foam flow rate depends non-linearly on
the applied gas pressure,
displaying a threshold pressure due to capillarity.
Strong discontinuities in the flow rate appear when the number of bubbles in the channel width changes, reflecting the discrete
nature of the foam topology.
We also produce an ultra flat foam, reducing the channel height from 250 μm to 8 μm, resulting in a height to diameter ratio
of 0.02; we notice a marked change in bubble shape during the flow. |
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Keywords: | 47 60 +i Flows in ducts channels nozzles and conduits 83 50 Ha Flow in channels 83 80 Iz Emulsions and foams |
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