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Overlimiting convection at a heterogeneous cation-exchange membrane studied by particle image velocimetry
| Citace: |
BELLOŇ, T. SLOUKA, Z. Overlimiting convection at a heterogeneous cation-exchange membrane studied by particle image velocimetry. JOURNAL OF MEMBRANE SCIENCE, 2022, roč. 643, č. MAR 1 2022, s. nestránkováno. ISSN: 0376-7388
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| Druh: | ČLÁNEK |
| Jazyk publikace: | eng |
| Anglický název: | Overlimiting convection at a heterogeneous cation-exchange membrane studied by particle image velocimetry |
| Rok vydání: | 2022 |
| Autoři: | tomáš Belloň , doc. Ing. Zdeněk Slouka Ph.D. |
| Abstrakt EN: | Electroconvection and gravitational convection are recognized as the primary mechanisms driving overlimiting currents in ion-exchange systems. Here, we use particle image velocimetry (PIV) to characterize the convection on a small piece of a commercially available heterogeneous cation-exchange membrane. We perform chronoamperometric measurements under various experimental conditions and simultaneously record the developed convection at the membrane-electrolyte solution interface using tracking particles. The convection is observed independently in horizontal and vertical planes, capturing flow fields pertinent to electroconvection and gravitational convection. PIV analysis computes velocity vector fields we employ to calculate the volumetric flow rate through a virtual semi-cylindrical wall around the membrane. The volumetric flow rate represents a way how to quantify the intensity of electroconvection. The electroconvection recorded on the horizontal plane manifests itself as a local short-range chaotic whirring localized at the membrane surface superimposed by two long-range counter-current vortices. The volumetric flow rate associated with the two counter-current vortices almost linearly increases with voltage and decreases with increasing concentration. The stagnant points of the vortices localize from 100 to 450 ?m away from the membrane. The convection observed on the vertical plane occurs as a result of electroconvection and gravitational convection. We show that gravitational convection eventually dominates and produces an upward-directed intensive flow with similar values of characteristic velocities as the electroconvection. The development of the gravitational convections is approximately one order of magnitude slower (on the order of seconds) than that of electroconvection (on the order of hundreds of milliseconds). |
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