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Tangential velocity measurements in a conical hydrocyclone operated with a fibre suspension
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2007 (English)In: Minerals Engineering, ISSN 0892-6875, Vol. 20, no 4, 407-413 p.Article in journal (Refereed) Published
Abstract [en]

The tangential velocity flow field in a conical hydrocyclone was measured using a self-cleaning pitometer. The influence of pulp fibre concentration on the tangential velocity profile was of particular interest.

The measurement, showed that the pulp fibres had a strong influence on the tangential velocity profile. When operating the hydrocyclone with pure water, the velocity profile showed the typical combination of free-vortex-like rotation close to the hydrocyclone wall and solid-body-like rotation in the proximity of the hydrocyclone axis. This profile changed significantly when pulp fibres were added. At a low fibre concentration (1.2 g/l), the fibres smoothened the transition between the free-vortex-like and the solid-body-like region of the velocity profile. The location of the maximum tangential velocity moved to a larger radius. At higher fibre concentration (7.5 and 11 g/l), the free-vortex-like behaviour in the outer area was virtually suppressed. Due to networking, the fibre suspension in the entire hydrocyclone behaved as a solid body.

The radial acceleration profile and tangential rate-of-strain profile were determined. Based on these profiles, a hypothesis was proposed explaining the well-known observation that fractionation efficiency decreases significantly at higher fibre concentrations.

Place, publisher, year, edition, pages
2007. Vol. 20, no 4, 407-413 p.
Keyword [en]
hydrocyclones; shear forces
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-6376DOI: 10.1016/j.mineng.2006.09.008ISI: 000245938600013OAI: diva2:11070
QC 20100701Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2010-08-04Bibliographically approved
In thesis
1. Flow Field and Fibre Fractionation Studies in Hydrocyclones
Open this publication in new window or tab >>Flow Field and Fibre Fractionation Studies in Hydrocyclones
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Hydrocyclones can be used to fractionate fibres according to their papermaking potential. The obtained fractions typically differ in fibre wall thickness and/or degree of fibre treatment. Despite a multitude of potential application scenarios, the process has so far had little commercial success. This is largely explained by the low fractionation efficiency and unfavourable operating characteristics of the process.

The fractionation efficiency of a hydrocyclone is closely related to its flow field. The influence of pulp concentration on the tangential velocity field was therefore studied, by using a self-cleaning pitometer. It was found that the pulp concentration had a strong influence on the tangential velocity. At a feed pulp concentration above 7.5 g/l, the suspension rotated almost as a solid body. As a consequence, the magnitude of radial acceleration and shear stresses decreased dramatically. It is suggested that this is detrimental to the fractionation efficiency.

The radial velocity field was measured using an Ultrasonic Velocity Profiler. The measurements showed that the rotational centre of the flow field did not correspond with the geometrical centre of the hydrocyclone. This displacement caused the tangential velocity component of the vortex to contribute substantially to the measurement result of the radial velocity component.

Based on the findings in respect to the flow field studies, a novel design for a fibre fractionation hydrocyclone was proposed. The flow field inside this hydrocyclone was compared to that in a conventional hydrocyclone. It was found, that high radial acceleration and shear stresses could be maintained in the novel design even at high fibre concentration. The fractionation efficiency of the novel hydrocyclone was characterised in terms of surface roughness difference between fine and coarse fraction. When operated with refined bleached softwood kraft pulp, the novel hydrocyclone could produce fractions with a substantial surface roughness difference without deteriorating the dewatering characteristics of the fine fraction. A low thickening of the reject is proposed to be the explanation for that. When fractionating TMP, the best efficiency occurred at a concentration of 10 g/l.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006
Trita-FPT-Report, ISSN 1652-2443 ; 2006:40
Fibre suspension, fractionation, hydrocyclone, measurement technique, velocity measurement, shear forces
National Category
Paper, Pulp and Fiber Technology
urn:nbn:se:kth:diva-4175 (URN)
Public defence
2006-12-01, STFI-salen, STFI-Packforsk, Drottning Kristinas väg 61, Stockholm, 10:10
QC 20100804Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2010-08-04Bibliographically approved

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Bergström, JonasVomhoff, Hannes
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