Liquid Dispersion Mechanisms in Agitated Tanks: Part Ii. Straight Blade and Disc Style Turbines

Chang, T.P.K.; Sheu, Y.-H.E.; Tatterson, Gary B.; Dickey, David S.

doi:10.1080/00986448108910935

Cited by 19 publications

(8 citation statements)

References 2 publications

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“…This regularity in the direction of drop elongation would indicate that breakup occurred in the anisotropic turbulent region. Experimental and modeling results presented by Konno et al (1983) and Chang et al (1981) suggest that the rms turbulent fluctuating velocities in regions where the flow regime is anisotropic could be important in the breakup of floc particles. Therefore, an increase in the rms fluctuating velocity with increasing tank size, as shown in this study, could explain why investigators have seen a degradation in flocculation performance with increasing tank size.…”

Section: Implication Of Experimental Results On Flocculation Performancementioning

confidence: 96%

“…However, if breakup occurred at scales where the flow regime is anisotropic or at scales outside the universal equilibrium range, then the maximum floc size cannot be uniquely described by 2 and can be influenced by flocculator geometry. Based on data from emulsification experiments, Konno et al (1983) and Chang et al (1981) displayed photographic evidence that a large portion of the oil droplets was broken behind the Rushton turbine blade. The breaking drops appeared to follow the outward flow along the impeller blade.…”

Section: Implication Of Experimental Results On Flocculation Performancementioning

confidence: 99%

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Turbulence in flocculators: Effects of tank size and impeller type

Ducoste

Clark

Weetman³

1997

AIChE Journal

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Section: Implication Of Experimental Results On Flocculation Performancementioning

confidence: 96%

Section: Implication Of Experimental Results On Flocculation Performancementioning

confidence: 99%

Turbulence in flocculators: Effects of tank size and impeller type

Ducoste

Clark

Weetman³

1997

AIChE Journal

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“…16 For dispersions with a low-viscosity dispersed phase it has been found that drops burst and several smaller drops of comparable size are obtained. 17,18 Whereas for high-viscosity drops, rupturing occurs via stretching leading to formation of bimodal distributions. 7,17,18 The results obtained in this work for the viscous subrange clearly point to a change in the pattern of evolution of drops-size distributions with viscosity ratio.…”

Section: Resultsmentioning

confidence: 99%

“…17,18 Whereas for high-viscosity drops, rupturing occurs via stretching leading to formation of bimodal distributions. 7,17,18 The results obtained in this work for the viscous subrange clearly point to a change in the pattern of evolution of drops-size distributions with viscosity ratio. Figure 3 presents typical time evolution of drop-size distributions for a lowviscosity oil phase, 0.65 cSt, and a high-viscosity silicon oil, 100 cSt (viscosity ratios of 0.49 and 96.50, respectively).…”

Section: Resultsmentioning

confidence: 99%

Viscosity effects in miniemulsification via ultrasound

Nazarzadeh

Sajjadi

2010

AIChE Journal

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“…However, the results may apply to more concentrated dispersions when coalescence is minimized by the presence of stabilizing agents (Valentas et al, 1966). In a turbulent stirred tank contactor, drop breakup is believed to be confined to the impeller region, and is due to variations in turbulent pressure along the drop's surface (Hinze, 1955) and to stretch-ing of globules in the trailing vortex system created by the impeller ( Ali et al, 1981;Chang et al, 1981).…”

Section: Introductionmentioning

confidence: 99%

Drop breakup in turbulent stirred‐tank contactors. Part I: Effect of dispersed‐phase viscosity

1986

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The extent to which dispersed-phase viscosity influences equilibrium mean drop size and drop size distribution at constant interfacial tension is determined for dilute suspensions by dispersing silicone oils of various viscosity grades in water. A mechanistic model for mean drop size is developed which predicts the moderate-viscosity data and whose parameters correlate the high-viscosity results. Trends in the mean size data coincide with those for the drop size distribution, which broadens considerably as viscosity increases and suggests a dependency on breakage mechanism.Drops are stabilized in dilute agitated liquid-liquid systems by surface and dispersed-phase viscous forces and are broken up by forces associated with the continuous-phase turbulence. Most studies have been limited to surface force stabilized dispersions, so the extent to which dispersed-phase viscosity influences mean drop size and drop size distribution is not well understood.For inviscid dispersed phases, equilibrium mean drop sizes produced by turbulent stirred-tank contacting processes are correlated by the well-known Weber number theory. This semiempirical theory, as applied to dilute suspensions, has been extended via mechanistic arguments to account for the effect of dispersedphase viscosity. A viscosity group, N,, is introduced which accounts for the importance of dispersed-phase viscosity relative to interfacial tension. Numerous experiments were conducted in four, baffled cylindrical tanks of standard geometry, equipped with six-blade Rushton turbines, by photographically examining dilute suspensions of silicone oils in water. Five grades of oil, ranging in viscosity from about 0.1 to 10 Pa -s and exhibiting the same interfacial tension with water ([0.0378 N / m), were employed. The range of variables studied includes 13,000 < Re < 101.000. 44 < We < 1.137, and 0.065 < < 0.50 m2/s3. The objectives of the experimental program were to examine the extent to which dispersed-phase viscosity influences equilibrium mean drop size and drop size distribution at constant interfacial tension, and to determine the relevance of the predicted correlating parameters and the range of applicability of the semiempirical theory.Results are compared to the data of Chen and Middleman (1967) for inviscid dispersed phases and the limited data of Arai et al. (1977) for viscous drops. Trends in the data are interpreted in light of the relevant correlating variables, the functional form of the drop size distribution, and the mechanism of drop breakup. AIChE JournalApril 1986 Vol. 32, No. 4 CONCLUSIONS AND SIGNIFICANCEThe experimental data have been analyzed and compared to the derived correlations and to literature data for inviscid dispered phases. The following conclusions apply to the range of variables studied.1. At constant conditions of agitation, the equilibrium drop size distribution broadens considerably as dispersed-phase viscosity, pd, increases. The size of the smallest drops decreases, while their number increases. The size of the largest drops ...

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Liquid Dispersion Mechanisms in Agitated Tanks: Part Ii. Straight Blade and Disc Style Turbines

Cited by 19 publications

References 2 publications

Turbulence in flocculators: Effects of tank size and impeller type

Turbulence in flocculators: Effects of tank size and impeller type

Viscosity effects in miniemulsification via ultrasound

Drop breakup in turbulent stirred‐tank contactors. Part I: Effect of dispersed‐phase viscosity

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