Boundary layer theory for mass and heat transfer in clouds of moving drops, bubbles or solid particles

Waslo, S.; Gal‐Or, Benjamin

doi:10.1016/0009-2509(71)83044-0

Cited by 34 publications

(11 citation statements)

References 27 publications

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“…This result validates the use of average mass-transfer coefficients to characterize microbubble mass transfer in experimental systems. The range of ka V predicted by the model compares favorably to the steady-state k values predicted by the theoretical model of Waslo and Gal-Or (32). The experimental KL,av values measured in pure water were similar in magnitude to the predicted ka V values.…”

supporting

confidence: 69%

Engineering Issues in Synthesis-Gas Fermentations

Worden¹,

Bredwell

Grethlein³

1997

ACS Symposium Series

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Biomass-derived synthesis gas can be readily converted into fuels and chemicals by anaerobic microorganisms. However, synthesis -gas fermentations typically exhibit low volumetric productivities due, in part, to low cell densities, production of unwanted by -products, and slow transfer of the synthesis gas into the liquid phase. Engineering approaches to improve bioreactor productivities are discussed, and recent advances in this area are summarized. Particular emphasis is placed on the use of bioreactor design to increase biocatalyst concentrations, development of metabolic models to study pathway regulation and the use of microbubble dispersions to enhance synthesis-gas mass transfer.Synthesis gas, which consists primarily of carbon monoxide (CO), and hydrogen (H 2 ), is produced by the partial oxidation of an organic feedstock at high temperature in the presence of steam. Although coal and petroleum have historically been the most commonly used feedstocks for synthesis-gas production, several new gasification plants have recently been based on biomass (7). Biomass offers several advantages over the traditional feedstocks. First, it has a much lower sulfur content than many coals. Synthesis gas produced from wood chips at the GE gasification plant in Schenectady, NY contained 28 ppm H 2 S (2), compared to 1-2% for coal-derived synthesis gases (3). Purification steps to remove sulfur from coal-derived synthesis gas are energy-intensive and add significantly to the product costs (4). Second, biomass materials are more reactive and thus require lower gasification temperatures and/or residence times. Fluidized-bed coal gasifiers are typically run at 1000°C using residence times of 0.5-3.0 h. By comparison, a temperature of 850°C was sufficient to gasify biomass using a residence time of 30 s to 5.0 min (5). Third, gasification of wood waste has the potential to solve a disposal problem while producing a valuable product. When wood waste is in

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supporting

confidence: 69%

Engineering Issues in Synthesis-Gas Fermentations

Worden¹,

Bredwell

Grethlein³

1997

ACS Symposium Series

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“…These average values of k L,av can be compared to steady‐state values from literature correlations. Waslo and Gal‐Or (8) used boundary‐layer theory to develop expressions for steady‐state mass‐transfer coefficients in clouds of moving bubbles. For a very dilute suspension of oxygen bubbles coated with surfactant, which gives a rigid bubble surface, their correlation predicts a k L value of 0.000 13 m/s.…”

Section: Resultsmentioning

confidence: 99%

“…(8) The total mass density of the liquid ( C ) and the diffusivity of A in the liquid ( D A ) are constant.…”

Section: Mathematical Modelmentioning

confidence: 99%

Mass-Transfer Properties of Microbubbles. 2. Analysis Using a Dynamic Model

Worden

Bredwell

1998

Biotechnol. Prog.

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Gas-to-liquid mass transfer is commonly the rate-limiting step in industrial fermentations. Microbubble sparging has been shown to give extremely high volumetric masstransfer rates, even for low power-to-volume ratios. Microbubbles are surfactantstabilized bubbles having a radius on the order of 25 µm. The extremely high surfacearea-to-volume ratios of microbubbles can result in rapid changes in their size, internal pressure, and gas composition. Consequently, an unsteady-state modeling approach is needed to adequately describe microbubble mass transfer. A dynamic model of a single microbubble immersed in an infinite pool of stagnant liquid was developed and solved numerically. The model accounts for mass-transfer resistances of the surfactant shell and surrounding bulk liquid, bubble shrinkage, changes in the gas pressure and composition inside the bubble, and changes in the liquid-phase concentration profile of the transferred gas surrounding the bubble. The model was used to explore a variety of dynamic phenomena associated with microbubble mass transfer. The presence of a nontransferred gas in the microbubble was predicted to significantly reduce the masstransfer rate, indicating that microbubble sparging is better suited to gases with a high consumable fraction. The instantaneous mass-transfer coefficient was predicted to change significantly with time, but the time-averaged coefficient was constant enough to justify the measurement of average mass-transfer coefficients for microbubbles. Average mass-transfer coefficients predicted by the model agreed well with values measured experimentally and calculated using literature correlations.

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“…Heat and mass transfer in non-Newtonian fluids is of great interest in many operations in the chemical and process engineering industries including coaxial mixers [1], blood oxygenators [2], milk processing [3], steady-state tubular reactors, and capillary column inverse gas chromatography devices [4], mixing mechanisms [5], bubble-drop formation processes [6], dissolution processes [7], and cloud transport phenomena [8]. Many liquids possess complex shear-stress relationships which deviate significantly from the Newtonian (NavierStokes) model.…”

Section: Introductionmentioning

confidence: 99%