Some effects of pseudoplasticity on hold-up in aerated, agitated vessels

Machoň, Václav; Vlček, Jiřı́; Nienow, Alvin W.; Solomon, John T.

doi:10.1016/0300-9467(80)85078-7

Cited by 34 publications

(34 citation statements)

References 10 publications

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“…At higher gas flow rate, power numbers are the same as in water or within the measurement errors. The small effect of rheology on P g has already been mentioned in the literature (Luong and Volesky, 1979; Machon et al, 1980). Therefore, to establish k L a correlations, power number values measured in water were preferred because a large amount of data was available.…”

Section: Resultsmentioning

confidence: 63%

Effect of tank size on k_La and mixing time in aerated stirred reactors with non‐newtonian fluids

et al. 2011

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The most important scale-up parameters of aerated bioreactors are investigated in 42 and 340 L vessels, with water and various xanthan gum and carboxymethyl cellulose solutions. The study focuses mainly on mass transfer (k L a) measurements under various operating conditions. The relevance of existing correlations is discussed. The traditional viscosity-contribution approach appears unable to predict the changes in k L a during scale-up and an alternative formulation is proposed. The effect of rheology on power consumption and mixing time is in fair agreement with works published on this topic.

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Section: Resultsmentioning

confidence: 63%

Effect of tank size on k_La and mixing time in aerated stirred reactors with non‐newtonian fluids

et al. 2011

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“…All the observations made in the CMC solutions in this work were also made by Ranade and Ulbrecht and Machon and Vlcek, who employed aqueous solutions of CMC in their hydrodynamic studies. Although they did not specifically measure bubble sizes in their experiments, they mentioned about the bubble flow patterns in the tank and the approximate bubble sizes in the liquids used.…”

Section: Resultsmentioning

confidence: 72%

“…This increase in coalescence inhibition is invoked by sodium ions that are present in the CMC solutions. Machon and Vlcek, in their study on gas dispersion in the CMC solutions, noted the presence of very small bubbles circulating in the liquid. The existence of these tiny bubbles was linked to the presence of sodium ions in the CMC solutions, which repressed coalescence.…”

Section: Resultsmentioning

confidence: 99%

Size distribution of bubbles in agitated viscous Newtonian and non‐Newtonian solutions

Momiroski

Bhattacharya

Davoody

et al. 2018

Asia-Pacific J Chem Eng

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The effects of impeller type, Newtonian shear thinning liquid viscosities, and noncoalescing conditions on the impeller gas cavities, impeller power consumption, and Sauter mean bubble diameter (d 32 ) in a multiphase agitated vessel were systematically studied. An underwater recording technique was used to study gas cavities and bubble size in various operating and design conditions. The gas cavity images were used to relate d 32 to gas cavity structure. It was observed that d 32 values increase with an increase in Newtonian and shear thinning liquid viscosities. Results also indicate that impellers operating in shear thinning liquids consume higher gassed power at the same operating conditions compared with those in Newtonian fluids. In addition, the d 32 values in noncoalescing liquids are substantially smaller compared with those in coalescing solutions at the same P g /V. Mathematical correlations are proposed for estimating the d 32 in the impeller discharge stream and P g /V in viscous Newtonian and non-Newtonian solutions.KEYWORDS bubble size, gas cavities, gas-liquid hydrodynamics, mathematical correlations, non-Newtonian liquid, power consumption Nomenclature and symbols:Greek letters: σ, surface tension, N/m; η, microscale of turbulence, m; ρ L , liquid phase density, kg/m 3 ; μ L , liquid phase viscosity, Pa·s; μ G , gas phase viscosity, Pa·s; τ, torque, N·m; v, kinematic viscosity of liquid, m 2 /s Letters and subscripts: a G-L , gas-liquid interfacial area, m 2 /m 3 ; C, impeller clearance, m; Ca c , critical capillary number, dimensionless; D, impeller diameter, m; d, particle size, m; d max , maximum stable diameter, m; d 32 , Sauter mean diameter, m; d bi , average bubble diameter in Equation (2), m; ε, energy dissipation rate, W/kg; G, strength of the applied strain rate around the bubble, 1/s; g, gravitational acceleration, m/s 2 ; H, liquid height, m; k, impeller constant; L, scale of the main flow, m; M s , mass of solids, kg; N, impeller speed, rps; n i , number of bubbles in Equation (2); N jsg , impeller speed for complete off-bottom solids suspension in three-phase systems, rps; N js , impeller speed for complete off-bottom solids suspension in two phase systems, rps; N P , power number; P g , gassed power input, W; S, dimensional coefficient; Q g , gas flow rate, vvm; T, tank diameter, m; V, liquid volume, m 3 ; V S , superficial gas velocity, m/s; vvm, volumetric flow rate of gas per minute per volume of liquid in the tank; u 2 , mean square velocity difference, m 2 /s 2 ; X, solid loading ratio, kg/kg Abbreviations: CMC, carboxymethyl cellulose; MIBC, methyl isobutyl carbinol

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“…The level measurements by Machon et al (1980) were carried out by means of a frequency unit for liquid level. Greaves and Barigou (1 990) used average conductivity in 5 points.…”

Section: Experimental Methods and Apparatusmentioning

confidence: 99%

“…Conductivity measurement results obtained in this study were checked by comparing with reference values for gas hold-up from the literature (see Table 1). The level measurements by Machon et al (1980) were carried out by means of a frequency unit for liquid level. Greaves and Barigou (1 990) used average conductivity in 5 points.…”

Section: Gas Dispersion Nonmentioning

confidence: 99%

Non‐uniformity of gas dispersion in turbine‐generated viscoelastic circulation flow

Vlaev

Martinov

1998

Can J Chem Eng

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Gas dispersion has been analysed experimentally by measuring local gas hold-up in two lab-scale conventional turbine-agitated vessels loaded with viscoelastic fluids. The gas hold-up radial profiles obtained in various axial positions close and far from the impeller reveal high non-uniformity of gas dispersion. Nonuniformity is quantified and related to elasticity, shear dependent viscosity, shear rate, first normal stress difference coefficient and type of fluid. The low values of gas hold-up obtained for the vessel central area are interpreted as hindered gas dispersion caused by the flow pattern specific for the viscoelastic properties of the circulating fluid. The paper is complementary to the effort for collecting up data for benchmarking numerical CFD simulations (Kumar et al., 1997).On a Ctudik expkrimentalement la dispersion de gaz en mesurant la rktention de gaz dans deux rkservoirs agitks B l'kchelle de laboratoire aliment& avec des fluides viscoklastiques. Les profils de rktention de gaz radiaux obtenus dans diverses positions axiales B proximitk ou B distance de la turbine rkvble une forte nonuniformitk de la dispersion de gaz. Cette non-uniformitk est quantifike et relike B l'klasticitk, h la viscositt dipendante du cisaillement, B la vitesse de cisaillement, au coefficient de diffkrence des contraintes normales primaires et au type de fluide. Les faibles valeurs de rktention de gaz obtenus pour la region centrale des rkservoirs sont interprktkes comme une dispersion de gaz entravke en raison du profil d'kcoulement spkcifique induit par les propriktks viscoklastiques du fluide circulant. Cet article vient complkter des efforts pour rkunir des donnkes pour des simulations numkriques (Kumar et al., 1997).Keywords: mixing and gas dispersion, viscoelastic systems, gas hold-up, non-uniformity. recent discussion on mixing in stirred non-Newtonian A fluids, Tatterson (1991) quotes differences of the main mixing parameters for viscoelastic solutions, e g , mixing time, power draw, circulation time. Emphasising on gas dispersion, the analyses (see Chhabra, 1993, Dekee et al., 1986) reveal significant viscoelastic effects on the behaviour of dispersed fluid particles. Bearing on the complexities of stirred flow, it has been realised that viscous and elastic flow properties influence the quality of gas dispersion in agitated reactors. However, analyses of the behaviour of structural macroparameters in stirred gas-liquid systems, such as local gas hold-up or bubble size distribution, are lacking. Apart from the studies of total gas hold-up in such type of fluids by Ranade and Ulbrecht (1978) and fluid flow mobility limitations noted by Wichterle and Wein (1981) and later by Nienow and Elson (1988), phenomenological descriptions of gas and liquid volumetric distribution in agitated non-Newtonian fluids are scarce. Regarding viscoelastic mixing flow patterns, the specific loops caused by shapepreserving forces in viscoelastic fluids (Ide and White, 1974; Hbcker et al, 1981) and the different discharge angles obse...

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Some effects of pseudoplasticity on hold-up in aerated, agitated vessels

Cited by 34 publications

References 10 publications

Effect of tank size on k_La and mixing time in aerated stirred reactors with non‐newtonian fluids

Effect of tank size on k_La and mixing time in aerated stirred reactors with non‐newtonian fluids

Size distribution of bubbles in agitated viscous Newtonian and non‐Newtonian solutions

Non‐uniformity of gas dispersion in turbine‐generated viscoelastic circulation flow

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Some effects of pseudoplasticity on hold-up in aerated, agitated vessels

Cited by 34 publications

References 10 publications

Effect of tank size on kLa and mixing time in aerated stirred reactors with non‐newtonian fluids

Effect of tank size on kLa and mixing time in aerated stirred reactors with non‐newtonian fluids

Size distribution of bubbles in agitated viscous Newtonian and non‐Newtonian solutions

Non‐uniformity of gas dispersion in turbine‐generated viscoelastic circulation flow

Contact Info

Product

Resources

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Effect of tank size on k_La and mixing time in aerated stirred reactors with non‐newtonian fluids

Effect of tank size on k_La and mixing time in aerated stirred reactors with non‐newtonian fluids