Time-dependent gas hold-up and bubble size distributions in a gas—highly viscous liquid—solid system

Kawalec-Pietrenko, B.

doi:10.1016/0300-9467(92)80017-5

Cited by 11 publications

(21 citation statements)

References 19 publications

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“…This occurs because several of the relative big bubbles moving from the separator penetrated the downcomer still deeper. On the other hand a slight decrease of the downcomer mass transfer coef®cient with an increase of the liquid viscosity was observed (Table 2), because the number of the small bubbles of diameter smaller than 1 mm increased as the liquid viscosity increased [5]. Simultaneously with an increase of the liquid viscosity the large bubbles gas hold-up decreased.…”

Section: Region-dependent Mass Transfer Ratementioning

confidence: 85%

“…The reason was probably the secondary¯ow, which generates usually in the corners of the rectangular cross-section canals. The bubble size distribution in the bubble swarm was more extended in the higher viscosity liquid [5]. There are the slowly rising small bubbles of diameter lower than 1 mm as well as large bubbles of diameter of tens of millimeters.…”

Section: Region-dependent Gas Hold-upmentioning

confidence: 96%

“…There are the slowly rising small bubbles of diameter lower than 1 mm as well as large bubbles of diameter of tens of millimeters. The gas volume in the large bubbles can be about 50% of the total gas hold-up [5]. The small bubble hold-up increased with an increase of the liquid viscosity and ®rst of all the small bubbles were transported into the downcomer.…”

Section: Region-dependent Gas Hold-upmentioning

confidence: 99%

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Region-dependent oxygen transfer rate in the rectangular airlift reactor

Kawalec-Pietrenko

Hołowacz

1998

Bioprocess Engineering

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Gas hold-up and the oxygen transfer in the zones of the internal loop airlift reactor with rectangular cross-section was studied. It was found, that the downcomer to the riser gas hold-up ratio depends on the gas ow rate, the physicochemical properties of the system and on the reactor height. The ratio of the downcomer mass transfer coef®cient to the global mass transfer coef®cient was less than 6%. The ratio of the downcomer to the global mass transfer coef®cient slightly increased with increase of the gas¯ow rate and decreased with increase of the liquid viscosity. The proposed correlation for the global overall mass transfer coef®cient predicts the experimental data well within 16.6% deviation. It was con®rmed that the reactor height is the important parameter for a design and a scale-up of the airlift reactors. List of symbolsa m length A m 2 cross-section area A ± proportionality constant in Eq. (9) b ± exponent in Eq. (9) b m width c ± exponent in Eq. (9) c kg á m A3 oxygen concentration in the liquid c Ã kg á m A3 equilibrium liquid phase dissolved-oxygen concentration d ± exponent in Eq. (9) d R m equivalent riser diameter (= 4´¯ow area/wetted perimeter) D m 2 á s A1 diffusivity in liquid phase DTAR ± cylindrical draft-tube airlift reactor ELAR ± cylindrical external loop airlift reactor Fr u 2 GR g Á d R Froude number g m á s A2 gravitational acceleration h R m reactor height Dh m difference between the liquid level in the upper and the lower piezometric tube Dh m m distance between the manometer tube location k L a s À1 liquid-phase volumetric mass transfer coef®cient Mo g 4 L Á g q L Á r 3 Morton number RILAR ± rectangular inner loop airlift reactor Sc g L q L Á D Schmidt number Sh k L a Á d 2 R D Sherwood number t s time, residence time t C s circulation time u GR m á s A1 super®cial gas velocity based on the riser cross-section u C m á s A1 mean liquid circulation velocityGreek letters e ± gas hold-up g mPa á s liquid dynamic viscosity q kg á m A3 density r mN á m A1 surface tension s s time-constant f ± correction factor in Eqs (3, 4)

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Section: Region-dependent Mass Transfer Ratementioning

confidence: 85%

Section: Region-dependent Gas Hold-upmentioning

confidence: 96%

Section: Region-dependent Gas Hold-upmentioning

confidence: 99%

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Region-dependent oxygen transfer rate in the rectangular airlift reactor

Kawalec-Pietrenko

Hołowacz

1998

Bioprocess Engineering

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“…Greek symbols e phase holdup e G established ®nal value of the total gas holdup in the reactor e Gr established ®nal value of the mean total gas holdup in the riser e GLB established ®nal value of the large bubble hold-up e GSB established ®nal value of the small bubble hold-up e GSt small bubble hold-up at the aeration time t e Gt total gas hold-up at the aeration time t Dh difference of the liquid heights in the upper and lower piezometric tubes Dh m distance between the location points of the piezometric tubes g a mPas apparent suspension viscosity g L mPas liquid viscosity q kg.m A3 density Aeration of the highly viscous liquids is especially of important signi®cance in biotechnology. An accumulation of small bubbles was observed during the aeration time of the highly viscous liquids in the bubble column [1,3,5,6,8,12,13,14]. Buchholz et al [1] and Peschke et al [12] found a large number of small bubbles in the aerated carboxymethyl cellulose solutions.…”

Section: B Kawalec-pietrenko W Pietrenkomentioning

confidence: 94%

“…Philip et al [13] described the mechanism of the generation of small bubbles. The contribution of the small bubble holdup to the total gas hold-up as well as the accumulation kinetics of small bubbles during the aeration of the highly viscous liquids in the bubble column was investigated by Kawalec-Pietrenko [5,6]. Heijnen et al [3] found that the overall mass transfer coef®cient values from the dynamic method are lower than the steady state values.…”

Section: B Kawalec-pietrenko W Pietrenkomentioning

confidence: 99%

Generation of small bubbles and small bubble-liquid mass transfer in airlift reactors containing highly viscous liquids

Kawalec-Pietrenko¹,

Pietrenko²

1999

Bioprocess Engineering

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The time-dependent gas hold-up is investigated during the aeration of the Saccharomyces cerevisiae suspension, the aqueous saccharose solutions and the glycerol solutions in the external loop airlift reactor. Due to the time-dependent bubble size distribution the fraction of the small bubble hold-up in the total gas hold-up decreases with an increase of the gas¯ow rate and with a decrease of the viscosity. The course of the accumulation process of the small bubbles is described by the ®rst-order kinetic equation. The small bubble accumulation rate is investigated in the airlift reactor and the bubble column. It is showed that the small bubbles form and disappear exclusively in the riser of the airlift reactor. It is found that the small bubble-liquid mass transfer coef®cient is several times larger than the overall oxygen transfer coef®cient. List of symbolsA d m 2 cross-section of the downcomer A r m 2 cross-section of the riser B, C parameters in the equation (10) D r m diameter of the riser D d m diameter of the downcomer D BC m diameter of the equivalent bubble column with the cross-section area equal to the sum of the riser and the downcomer cross-section areas H m height of the unaerated liquid (suspension) k s A1 accumulation rate constant of the small bubbles k d s A1 disengagement rate constant of the small bubbles k L a SB s A1

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Influence of impeller type on hydrodynamics and gas‐liquid mass‐transfer in stirred airlift bioreactor

et al. 2015

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The influence of impeller type in a mechanically stirred airlift bioreactor was analyzed in relation to the non‐Newtonian viscous fluids. The agitation was carried out through a marine impeller (axial impeller) and a paddle impeller (radial impeller) located along with the gas sparger in the region comprised by the riser. The bioreactor was sparged with air under different velocities (0.036–0.060 m s−1). Carboxymethylcellulose 1.94% and xanthan 1.80% were used as a fluid model. The gas holdup and volumetric mass‐transfer coefficient increased in up to five and three times, respectively, when compared to a conventional airlift bioreactor; however, better results were obtained when the straight paddle impeller type was used. The results suggest that the studied bioreactor can be used successfully in viscous fluid, and it can be more efficient than conventional airlift bioreactors. The results obtained suggest the use of radial impellers. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3159–3171, 2015

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Time-dependent gas hold-up and bubble size distributions in a gas—highly viscous liquid—solid system

Cited by 11 publications

References 19 publications

Region-dependent oxygen transfer rate in the rectangular airlift reactor

Region-dependent oxygen transfer rate in the rectangular airlift reactor

Generation of small bubbles and small bubble-liquid mass transfer in airlift reactors containing highly viscous liquids

Influence of impeller type on hydrodynamics and gas‐liquid mass‐transfer in stirred airlift bioreactor

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