Effect of scale-up on average shear rates for aerated non-Newtonian liquids in external loop airlift reactors

Al-Masry, Waheed A.

doi:10.1002/(sici)1097-0290(19990220)62:4<494::aid-bit14>3.0.co;2-6

Cited by 29 publications

(19 citation statements)

References 26 publications

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“…The knowledge of shear-rate and the resulting stress distribution in aerated non-Newtonian liquids are important for determining whether a bioreactor is suitable to handle shearsensitive biosystems [4]. In the recent literature, few attempts have so far been made to analyze numerically the drop or bubble behavior in non-Newtonian fluids.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of a bubble rising in shear-thinning fluids

Zhang

Yang

Mao

2010

Journal of Non-Newtonian Fluid Mechanics

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a b s t r a c tThe motion of a single bubble rising freely in quiescent non-Newtonian viscous fluids was investigated experimentally and computationally. The non-Newtonian effects in the flow of viscous inelastic fluids are modeled by the Carreau rheological model. An improved level set approach for computing the incompressible two-phase flow with deformable free interface is used. The control volume formulation with the SIMPLEC algorithm incorporated is used to solve the governing equations on a staggered Eulerian grid. The simulation results demonstrate that the algorithm is robust for shear-thinning liquids with large density ( 1 / g up to 103 ) and high viscosity (Á 1 /Á g up to 10 4 ). The comparison of the experimental measurements of terminal bubble shape and velocity with the computational results is satisfactory. It is shown that the local change in viscosity around a bubble greatly depends on the bubble shape and the zero-shear viscosity of non-Newtonian shear-thinning liquids. The shear-rate distribution and velocity fields are used to elucidate the formation of a region of large viscosity at the rear of a bubble as a result of the rather stagnant flow behind the bubble. The numerical results provide the basis for further investigations, such as the numerical simulation of viscoelastic fluids.

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Section: Introductionmentioning

confidence: 99%

Numerical simulation of a bubble rising in shear-thinning fluids

Zhang

Yang

Mao

2010

Journal of Non-Newtonian Fluid Mechanics

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“…The criticism made of the Nishikawa et al [8] equation has been discussed in detail elsewhere [9]. Al-Masry's [15] model is relatively simple and predicts shear rates with reasonable accuracy in bioreactors and would be used for gas holdup corrections in this study. From Eq.…”

Section: Resultsmentioning

confidence: 96%

“…A comparison of the various models for shear rates (and hence shear stress) could be chosen from Eqs. (4) through (15). The comparison of the various models was established by simulating shear rates in the 150 dm 3 circulating bubble column, and is shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

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Gas Holdup in Circulating Bubble Columns with Pseudoplastic Liquids

Al-Masry¹

2001

Chem. Eng. Technol.

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The contributions of pressure drop due to wall frictional losses to the total gas holdup of two‐phase viscous non‐Newtonian systems were experimentally investigated using a 150 dm3 circulating bubble column. The column had a downcomer‐to‐riser cross‐sectional area ratio of 0.54 and a dispersion height of 2.5 m. Aqueous solutions of xanthan gum and carboxymethyl cellulose were used to simulate a wide range of rheological properties. The average wall shear stress was estimated from Al‐Masry's (1999) correlation for the average wall shear rate in external loop airlift reactors. Pressure drop due to wall shear stress was found significantly contributed by 10–70 % to the total gas holdup. This contribution has always been ignored in the data presented in the literature due to the absence of reliable and simple correlations for the average shear rate and shear stress. Corrections to gas holdup were found necessary for non‐Newtonian solutions with concentrations of ≥ 0.5 wt/wt.‐%.

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“…As Nf °c C/(d 2 L), NfL 3 oc CL 2 /d 2 . It is known that the crowding number N oc CL 2 /d 2 ; thus, the effective viscosity is a function of the crowding number N. Shamlou et al (1998) and Al-Masry (1999) showed that shear rate is a function of superficial gas velocity in non-Newtonian liquids, which indicates that the effective viscosity in a fiber suspension is also a function of superficial gas velocity.…”

Section: Homogeneous and The First Part Of The Transitional Flow Regimentioning

confidence: 99%

Gas holdup in a gas-liquid-fiber semi-batch bubble column

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Effect of scale-up on average shear rates for aerated non-Newtonian liquids in external loop airlift reactors

Cited by 29 publications

References 26 publications

Numerical simulation of a bubble rising in shear-thinning fluids

Numerical simulation of a bubble rising in shear-thinning fluids

Gas Holdup in Circulating Bubble Columns with Pseudoplastic Liquids

Gas holdup in a gas-liquid-fiber semi-batch bubble column

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