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Literature review of experimental hydrocyclone flow field studies
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2007 (English)In: Separation and Purification Technology, ISSN 1383-5866, Vol. 53, no 1, 8-20 p.Article in journal (Refereed) Published
Abstract [en]

The complex flow field of hydrocyclones has been experimentally investigated on several occasions. Most studies present similar results for the tangential velocity component. In the inner part of the cyclone, it resembles a solid-body rotation, while it typically has a free-vortex-like behavior in the outer part. When looking at the axial velocity component, the results are more diversified. Most studies show a downward velocity close to the wall and an upward velocity in the center. However, some studies report a heavily varying axial velocity over short radii close to the centerline. The radial velocity component appears to be the most problematic one to measure. Dissimilarities in measurement results between the studies are often greater than similarities. However, later studies agree on an increasing inward radial velocity towards the hydrocyclone center. Despite the obvious relationship, extremely little experimental research work can be found in the literature where changes to the flow field are connected to changes in separation efficiency.

Place, publisher, year, edition, pages
2007. Vol. 53, no 1, 8-20 p.
Keyword [en]
Hydrocyclones; Measurement techniques; Fluid mechanics
National Category
Mathematics
Identifiers
URN: urn:nbn:se:kth:diva-6374DOI: 10.1016/j.seppur.2006.09.019ISI: 000243881600002OAI: oai:DiVA.org:kth-6374DiVA: diva2:11068
Note
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
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:40
Keyword
Fibre suspension, fractionation, hydrocyclone, measurement technique, velocity measurement, shear forces
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-4175 (URN)
Public defence
2006-12-01, STFI-salen, STFI-Packforsk, Drottning Kristinas väg 61, Stockholm, 10:10
Opponent
Supervisors
Note
QC 20100804Available from: 2006-11-22 Created: 2006-11-22 Last updated: 2010-08-04Bibliographically approved

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