Electroconvective enhancement of mass or heat exchange between a drop or bubble and surroundings in the presence of an interfacial tension gradient

Chang, Loto S.; Berg, John C.

doi:10.1002/aic.690310118

Cited by 12 publications

(2 citation statements)

References 9 publications

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“…Circulation inside a drop or a bubble suspended in a continuous phase, induced by an electric field, was first reported by Taylor (1966) and later by many researchers including Chang and co‐workers (Chang and Berg, 1985a,b). However, in all these studies, the emphasis was on the role of interfacial tension on the circulation flow and in turn on heat and mass transfer.…”

Section: Resultsmentioning

confidence: 95%

Electrokinetic Demixing of Aqueous Two-Phase Systems. 3. Drop Electrophoretic Mobilities and Demixing Rates

et al. 1998

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Scale-up of aqueous two-phase extraction, which is useful in the isolation and purification of certain bioproducts, is limited by the slow demixing rates of the two aqueous phases. Electrokinetic demixing has been shown to increase by more than 5-fold the demixing rates of systems up to 100 mL in volume in a manner that depends on field strength, field polarity, pH, and phase composition. The present study is an attempt to relate demixing rates to droplet electrokinetic mobilities which were measured microscopically and inferred from demixing data. A clear dependence of demixing rate was observed on drop electrophoretic mobility and pH. The electrophoretic mobility of individual phase droplets suspended in the other phase was measured for poly(ethylene glycol)/Dextran systems using a microelectrophoresis unit and compared with mobilities predicted by electrokinetic theory. We confirmed earlier reports that the droplet electrophoretic mobility increased with increasing drop diameter and explained this increase on the basis of an internal electroosmotic flow model. Effective electrophoretic mobilities were estimated from electrokinetic demixing data in a 100-mL column and compared with predicted as well as experimentally measured values of electrophoretic mobility. The mobilties increased with increased phosphate ionization due to change in pH irrespective of the sign (or polarity) of the applied electric field. The electroosmotic flow model could explain satisfactorily the following two paradoxes: (1) the direction of migration of drops is the opposite of that predicted by colloid electrokinetics and (2) the phase demixing rate increased irrespective of the sign of the applied electric field.

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Section: Resultsmentioning

confidence: 95%

Electrokinetic Demixing of Aqueous Two-Phase Systems. 3. Drop Electrophoretic Mobilities and Demixing Rates

et al. 1998

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“…Diffusivities of salts were obtained from Chang and Myerson (1985), and were measured at 25°C. Solubilities at 0°C for gases were calculated using Henry’s law constants (Sanders, 1999), and for salts obtained from Haynes (2012) .…”

Section: Resultsmentioning

confidence: 99%

Freeze/Thaw-Induced Embolism: Probability of Critical Bubble Formation Depends on Speed of Ice Formation

Sevanto¹,

Holbrook²,

Ball³

2012

Front. Plant Sci.

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Bubble formation in the conduits of woody plants sets a challenge for uninterrupted water transportation from the soil up to the canopy. Freezing and thawing of stems has been shown to increase the number of air-filled (embolized) conduits, especially in trees with large conduit diameters. Despite numerous experimental studies, the mechanisms leading to bubble formation during freezing have not been addressed theoretically. We used classical nucleation theory and fluid mechanics to show which mechanisms are most likely to be responsible for bubble formation during freezing and what parameters determine the likelihood of the process. Our results confirm the common assumption that bubble formation during freezing is most likely due to gas segregation by ice. If xylem conduit walls are not permeable to the salts expelled by ice during the freezing process, osmotic pressures high enough for air seeding could be created. The build-up rate of segregated solutes in front of the ice-water interface depends equally on conduit diameter and freezing velocity. Therefore, bubble formation probability depends on these variables. The dependence of bubble formation probability on freezing velocity means that the experimental results obtained for cavitation threshold conduit diameters during freeze/thaw cycles depend on the experimental setup; namely sample size and cooling rate. The velocity dependence also suggests that to avoid bubble formation during freezing trees should have narrow conduits where freezing is likely to be fast (e.g., branches or outermost layer of the xylem). Avoidance of bubble formation during freezing could thus be one piece of the explanation why xylem conduit size of temperate and boreal zone trees varies quite systematically.

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The effect of electric field on mass transfer from drops dispersed in a viscous liquid

He¹,

Baird²,

Chang³

1993

Can. J. Chem. Eng.

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Mass transfer of benzoic acid from drops dispersed into a continuous phase of mineral oil with high viscosity has been investigated both with and without an imposed non‐uniform d.c. electric field. Total mass transfer efficiency was significantly enhanced in the presence of the high voltage electric field. The results indicate that the application of the electric field to the drop formation process does not change the fundamental mass transfer mechanisms and the mass transfer during drop free fall can also be described by existing mass transfer models. The results also suggest that the high viscosity of the continuous phase inhibits the drops oscillation as well as circulation when the drop sizes become smaller under the applied high voltage electric field. Therefore the significant enhancement of mass transfer efficiency in the present work is mainly due to the increased specific interfacial area.

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Electroconvective enhancement of mass or heat exchange between a drop or bubble and surroundings in the presence of an interfacial tension gradient

Cited by 12 publications

References 9 publications

Electrokinetic Demixing of Aqueous Two-Phase Systems. 3. Drop Electrophoretic Mobilities and Demixing Rates

Electrokinetic Demixing of Aqueous Two-Phase Systems. 3. Drop Electrophoretic Mobilities and Demixing Rates

Freeze/Thaw-Induced Embolism: Probability of Critical Bubble Formation Depends on Speed of Ice Formation

The effect of electric field on mass transfer from drops dispersed in a viscous liquid

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