Scale Effects on Hydrodynamic and Mass Transfer Characteristics of External Loop Airlift Reactors

Benyahia, Farid; Jones, Lynn

doi:10.1002/(sici)1097-4660(199707)69:3<301::aid-jctb716>3.0.co;2-z

Cited by 28 publications

(21 citation statements)

References 8 publications

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“…Mass transfer is one of the most significant factors in process design and reactor scale up, and has been intensively studied in airlift reactors during the past decades [3][4][5][6][7][8][9]. However, most of these studies have focused on experimental determination of the volumetric mass transfer coefficient (k l a), which is a global parameter that depends on reactor geometry, operating conditions and phase properties [7,[10][11][12][13][14]. The common approach to describe k l a is to correlate it with the factors that affect it.…”

Section: Introductionmentioning

confidence: 99%

Gas holdup, bubble behavior and mass transfer in a 5m high internal-loop airlift reactor with non-Newtonian fluid

Deng

Wang

Zhang

et al. 2010

Chemical Engineering Journal

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Section: Introductionmentioning

confidence: 99%

Gas holdup, bubble behavior and mass transfer in a 5m high internal-loop airlift reactor with non-Newtonian fluid

Deng

Wang

Zhang

et al. 2010

Chemical Engineering Journal

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“…Gas–liquid mass transfer and species transport in chemical and bioreactors have been investigated for many decades as a basis for rational design, operation, and scale‐up of these reactors. In most studies, experimental methods that assume a perfectly mixed batch reactor were used 11, 31, 32. This technique is based on the measurement of the time evolution of the average dissolved gas concentration in the reactor.…”

Section: Introductionmentioning

confidence: 99%

Flow and mass transfer of fully resolved bubbles in non‐Newtonian fluids

2007

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In this work, high-resolution 2-D numerical simulations were performed on the motion of deformable bubbles in non-Newtonian fluids and the associated mass transfer. For that purpose, we have implemented a semi-Lagrangian advection scheme and improved the fluid dynamic calculation by the usage of implicit algorithms. Non-Newtonian fluids are described by generalized Newtonian as well as viscoelastic model fluids. As shear-thinning model we use a Power-Law and a Carreau-Yasuda model, the viscoelastic fluid simulations are based on an Upper-Convected Maxwell model combined with a recently introduced model for the evolution of the effective shear rate. The mathematical challenges arising from the hyperbolic nature of the resulting set of equations are addressed by inclusion of artificial diffusion in the stress equation. In our work, it was found that shear thinning effects have impact on collision rates, and therefore, may influence coalescence of bubbles in non-Newtonian liquids. Furthermore, for the first time, concentration fields of dissolved gas in viscoelastic fluids are presented. The study shows that the fluid elasticity plays a major role for bubble rise velocity, and therefore, mass transfer. As the wake dynamics differ significantly from that in Newtonian liquids, abnormal mixing characteristics can be expected in the bubbly flow of viscoelastic fluids. 2007 American Institute of Chemical Engineers AIChE J, 53: [1861][1862][1863][1864][1865][1866][1867][1868][1869][1870][1871][1872][1873][1874][1875][1876][1877][1878] 2007 Keywords: numerical simulation, bubbles, non-Newtonian liquids, mass transfer IntroductionBecause of persistent uncertainties in the underlying models and system properties, the scale-up of bioreactors remains a challenging problem. For example, the rheology of media in bioreactors is non-Newtonian in most cases. [1][2][3][4][5][6][7][8] However, details of the non-Newtonian fluid characteristics, such as viscoelasticity or the tendency for shear thinning, are frequently unknown or neglected. Furthermore, in contrast to Newtonian media, there is a lack of general correlations for mass and heat transfer rates, which are needed for the prediction of oxygen supply and heat removal. Similar observations can be made for the properties needed to precisely predict transport of metabolites, nutrients, or CO 2 . So far, most studies are based on experimental investigations, which are usually interpreted with simple theoretical models. 3,4,[8][9][10][11] principles methods to predict mass-transfer coefficients, transport rates, and other parameters in non-Newtonian fluids have not been reported so far. Local mass transfer is not the only micro-effect of central importance in the design of bioreactors. Knowledge of the localized forces, such as shear and normal stresses in the cell's microenvironment, is also a key for determining whether a bioreactor is suitable to handle sensitive biosystems.12 Subcritical shear stresses found in the hydrodynamic environment of large-scale reactors may redu...

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“…Furthermore, optimum ratio between the diameter of the riser and the downcomer (i.e. D r / D d ) was reported to be between 1.0 and 3.0 , , . As shown in Fig.…”

Section: Methodsmentioning

confidence: 90%

“…This class of bioreactors is divided into two main subclasses of internal and external loop airlift bioreactors. The main difference in the design of the external loop airlift bioreactors is that the liquid circulation in the riser and downcomer takes place in two separate compartments, which are connected by a pipe at the bottom and a pipe or a tank at the top . This design leads to maximum deaeration in the gas disengagement section of the external loop airlift bioreactors.…”

Section: Introductionmentioning

confidence: 99%

Dynamic and local gas holdup studies in external loop recirculating airlift reactor with two rolls of fiberglass packing using electrical resistance tomography

Hamood-Ur-Rehman

Ein‐Mozaffari

Dahman

2012

J of Chemical Tech & Biotech

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BACKGROUND: Airlift bioreactors have been used extensively in biotechnology industries in recent years in a variety of arrangements and applications. The insertion of packing inside the bioreactors has the potential to provide high productivity within a compact size through utilizing immobilized species. RESULTS: A novel recirculating external loop airlift bioreactor that has two rolls of fiberglass packing and a gas distributor in between was designed and built. Electrical resistance tomography (ERT) images showed that the gas holdup increased after installing the packing and the gas distributor. Gas holdup in the riser increased with decreasing static liquid height in the bioreactor. This decreased the liquid superficial velocity, which contributed to a higher gas holdup in the bioreactor. Results also showed that riser gas holdup varied slightly with different sparger configurations. Higher gas holdup increases the oxygen mass transfer rate by increasing the residence time and interfacial mass transfer area. CONCLUSION: ERT results showed that fiberglass packing with an installed gas distributor in bioreactors can achieve higher gas holdup at higher superficial gas velocity. This can contribute to improved conversion in bioreactors with packing through utilizing higher biomass concentrations and higher oxygen concentration. © 2012 Society of Chemical Industry

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Scale Effects on Hydrodynamic and Mass Transfer Characteristics of External Loop Airlift Reactors

Cited by 28 publications

References 8 publications

Gas holdup, bubble behavior and mass transfer in a 5m high internal-loop airlift reactor with non-Newtonian fluid

Gas holdup, bubble behavior and mass transfer in a 5m high internal-loop airlift reactor with non-Newtonian fluid

Flow and mass transfer of fully resolved bubbles in non‐Newtonian fluids

Dynamic and local gas holdup studies in external loop recirculating airlift reactor with two rolls of fiberglass packing using electrical resistance tomography

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