Flow measurements on a turbulent fiber suspension by laser Doppler anemometry

Andersson, Sven; Rasmuson, Anders

doi:10.1002/aic.690460603

Cited by 17 publications

(35 citation statements)

References 11 publications

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“…The turbulence intensity increased in the small length scales only when the crowding factor was small (for example, N Ϸ 3.6), or when the crowding factor was in the medium range and the flow was in the wall region. The suppression of the small-scale components of the turbulence spectrum by fiber addition was also reported by Andersson and Rasmuson 9 and Forgacs et al, 10 who further concluded that the suppression was stronger at higher fiber mass fractions.…”

Section: Introductionsupporting

confidence: 55%

Gas‐liquid‐fiber flow in a cocurrent bubble column

Tang

Heindel

2005

AIChE Journal

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Section: Introductionsupporting

confidence: 55%

Gas‐liquid‐fiber flow in a cocurrent bubble column

Tang

Heindel

2005

AIChE Journal

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“…Similar patterns were found for the mean tangential velocity (see Figure 13). Analogous measurements were reported by Andersson and Rasmuson (2000) for similar systems but without the presence of gas. The results of this work agree with theirs, which also explain the fact that the RMS and the mean velocities are rather high close to the wall.…”

Section: Radial Profi Les For the Case Of 12% Wt Fibres And 10% Volmentioning

confidence: 94%

“…range with gas contents up to 15% vol. The two transition points, found by Andersson and Rasmuson (2000), were detected also with gas present and appear at higher impeller speeds with increasing gas and fi bre concentrations. Plotting RMS and mean velocities versus impeller speed and power input, it is found that both decrease with increasing gas and fi bre contents.…”

mentioning

confidence: 84%

“…Another fl ow phenomenon that occurs is that the fi bres damp the turbulence, which was shown by Andersson and Rasmuson (2000). Using LDA, they determined the power spectrum and found a suppression of the turbulence at wave numbers corresponding to fl oc size.…”

Section: Infl Uence Of Fibre Concentrationmentioning

confidence: 97%

“…The same rotary shear tester used in the work by Andersson and Rasmuson (2000) is used here. The model system comprises a refractive-index matched suspension in the 4-12% wt.…”

mentioning

confidence: 99%

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LDA Measurements on a Turbulent Gas/Liquid/Fibre Suspension

Pettersson

Rasmuson

2004

Can J Chem Eng

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T he three-phase system gas/liquid/fi bre suspension is of great importance in many industrial systems, particularly in the manufacture of pulp. Both separating a gas phase from a fi bre suspension and mixing them are important processes. Pulp fi bre processing is commonly carried out in the medium-consistency (MC) range where the mass concentration of the suspension is between 0.03 and 0.15. MC technology has the potential to decrease not only water and energy consumption but also equipment dimensions. This is of particular importance in connection with the closing of mills. The disadvantages are associated with the more diffi cult processing of the fi bre suspension in operations such as screening, pumping, washing and mixing.The accumulation of gas in centrifugal pumps was one of the fi rst problems encountered when MC technology was introduced (Gullichsen and Härkönen, 1981). Centrifugal forces in the pumps caused an effi cient phase separation and accumulated gas around the pumping wheel prevented further operation. The problem was solved early with vacuum pumps removing excess air from the centre of the pump. Flotation de-inking of wastepaper involves the use of air bubbles to remove hydrophobic particles from wastepaper slurries. Ideally, a homogeneous system would provide more effi cient fl otation but bubble sizes and rise velocities are also very important. Radiographic images reveal that gas fl ow characteristics are substantially altered in the presence of fi bres (Heindel and Monefeldt, 1998).In pulp bleaching operations, gaseous reagents are often mixed into pulp suspensions. The introduction of ozone bleaching in particular has, however, caused complications. The reaction is extremely fast, which makes good gas dispersion essential. Poor dispersion leads to low selectivity, producing unevenly bleached fi bres and degraded fi bres. Byrd et al. (1992) review the literature of ozone bleaching and delignifi cation. When gases are mixed into pulp suspensions, it is important to achieve good mixing over the macro-scale, fi bre-scale and microscale. This ensures the uniform distribution of reagents throughout the suspension and leads to uniform bleaching. Bennington (1993) was the fi rst to make a thorough investigation of the mixing of gases into MC pulp suspensions. Using a high-speed video system, he identifi ed six different fl ow regimes, which were correlated to the power input, pulp consistency and volume fraction of the gas phase. Most of these regimes are less turbulent than is the case in this work. As far as is known, however, no detailed fl ow characterization has been performed on this three-phase fl ow system. Detailed fl ow measurements on a turbulent fi bre suspension (without gas) by Laser Doppler Anemometry (LDA) were reported in earlier work by Andersson and Rasmuson (2000). The measurements were performed on a refractive-index matched glass-fi bre suspension in the 3-20% wt. range. It was found that the liquid fl ow of such suspensions underwent two transitions: the Detailed continuous...

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