Gas holdup and axial dispersion in gas-liquid concurrent bubble column.

Wachi, Shun; Morikawa, Hisashi; Ueyama, Korekazu

doi:10.1252/jcej.20.309

Cited by 39 publications

(12 citation statements)

References 4 publications

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“…In other instances, a more complex relationship between axial dispersion coefficient and the gas flow rate may exist. Thus, for any fixed value of gas flow rate, increases in the concurrent liquid flow velocity are known to produce a decline in the value of axial dispersion coefficient [24]. This is because, for a fixed gas flow rate, increasing (55) and (56)) are shown for the riser and the downcomer.…”

Section: Resultsmentioning

confidence: 99%

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Rubio

García

Molina

et al. 2001

Chemical Engineering Journal

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Models were developed for prediction and interpretation of the observed steady-state axial dissolved oxygen concentration profiles in tall airlift bioreactors. The observed concentration profiles were non-linear because of a combination of hydrodynamic and mass transport factors. The profiles were influenced mainly by the liquid-phase axial dispersion coefficient, the volumetric overall gas-liquid mass transfer coefficient, the gas velocity, the induced liquid circulation velocity. The model-predicted concentration profiles agreed within ±2% with the measured data in a tall (working aspect ratio ∼ 15) airlift vessel operated under aeration regimens that are typically used during wastewater treatment. Axial inhomogeneities in dissolved oxygen increased with increasing aeration rate. This phenomenon may influence activated sludge processes in airlift and deep-shaft reactors. The maximum attainable concentration of dissolved oxygen at the bottom of a typically aerated airlift reactor, ≥ 3.5 m deep, always remained at <80% of air saturation value even when oxygen was not being consumed. Also, at steady state and without a net transfer of oxygen, the gas-phase mole fraction of oxygen varied by > 10% axially up the reactor.

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Section: Resultsmentioning

confidence: 99%

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Rubio

García

Molina

et al. 2001

Chemical Engineering Journal

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“…(1981), Joshi (1983), Walter and Blanch (1983), Ulbrecht et al (1985) Yang et al (1986), Wachi et al (1987), Clark et al (1987) and Kawase and Moo-Young (1989).…”

Section: Modelling Of Liquid Phase Flow Patternmentioning

confidence: 99%

Sparged loop reactors

et al. 1990

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Circulating bubble columns or loop reactors form one of the important classes of modified bubble columns. The present paper analyses the performance of external loop air lift reactors (EL‐ALR). The EL‐ALR has many advantageous features especially at large scale. These arise from its feature of having controlled liquid circulation which is the key parameter for the design and operation of EL‐ALR contactors. Therefore, a reliable and generalised circulation model has been presented. The reliability of the model depends on the accuracy of the predictive methods for the gas hold‐up and the two‐phase fractional pressure drop. Detailed analysis of these fundamental parameters of gas‐liquid flows has been presented. The effects of design (area ratio of riser to downcomer, height to diameter ratio and volume of reactor) and operating (gas flow rates and sparging locations) parameters on the performance of the EL‐ALR have been analysed in detail. A rational basis has been developed for the estimation of pressure drop, mixing time and mass transfer coefficient. An optimum combination of design and operating parameters has been suggested and a criterion has been developed for the optimum location of spargers. An attempt has been made to provide critical analysis of the published information and to construct a coherent picture of EL‐ALR.

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“…They will k grouped into two sections: overall (average) and local phase holdup. (Hikita et al, 1980;Miller, 1980;Fan et al, 1985;Reilly et al, 1986;Wachi et al, 1987;Prakash, 1991;Del Pozo, 1992;Gandhi, 1997 (Akita and 'fahida, 1973;Kato et al, 1973;Grover et al. 1986;Hatate et al, 1986;Morooka et al, 1986;Ozturk et al, 1987 2)The design of gas and liquid sparger plays a vital role in limiting the magnitude of the erron.…”

Section: Phase Holdup Measurement Techniquementioning

confidence: 99%

“…Aiso due to limitations in the probe design, some probes cannot detect small bubbles of diameters less than 1 mm (Hudson, 1996). Wachi et al ( 1987) found that the probe technique failed to detect 30 % of the gas holdup.…”

Section: Electroconductivity Techniquementioning

confidence: 99%

Heat Transfer and Hydrodynamics in a Three-Phase Slurry Bubble Column

Prakash

1997

Ind. Eng. Chem. Res.

102

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The instantaneous and time-averaged heat transfer coefficients in the regions near the wall and at the center and average gas holdups were measured in a 0.28 m diameter slurry bubble column for the air−water and air−water−glass beads (35 μm) system. The effects of high gas velocities (up to 0.35 m/s) and high solids concentrations (up to 40 vol %) were investigated. Gas holdup decreased with increasing slurry concentrations; the rate of decline was rapid at high gas velocities. The instantaneous local heat transfer measurements were analyzed to study the bubble behavior in the regions near the wall and at the center for different solids concentrations. Larger bubbles were detected in the wall region in slurry systems compared to the solid-free system. The average heat transfer coefficient decreased with increasing slurry concentrations. The heat transfer coefficient was always lower at the wall than at the center.

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Gas holdup and axial dispersion in gas-liquid concurrent bubble column.

Cited by 39 publications

References 4 publications

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Axial inhomogeneities in steady-state dissolved oxygen in airlift bioreactors: predictive models

Sparged loop reactors

Heat Transfer and Hydrodynamics in a Three-Phase Slurry Bubble Column

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