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Application of a pitometer to measure the tangential velocity in a cylindrical through-flow hydrocyclone operated with a fiber suspension
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2005 (English)In: Nordic Pulp and Paper Research Journal, ISSN 0283-2631, Vol. 20, no 1, 30-35 p.Article in journal (Refereed) Published
Abstract [en]

This investigation evaluates a novel fluid velocity measurement method to measure the tangential velocity in a hydrocyclone. The hydrocyclone was operated with an opaque fiber suspension in order to investigate the influence of fiber presence on the tangential velocity distribution. The tangential velocity was measured with a one-hole pitometer, 0.9 mm in diameter, that was equipped with a micro pressure transducer. The pitometer was kept clean with a continuous purge flow. The probe was tested in a cylindrical through-flow hydrocyclone operated with water and 0.4 g/l and 0.8 g/l (0 %, 0.04 % and 0.08 %) addition of a bleached softwood kraft pulp. The velocity profiles measured in pure water agreed qualitatively with velocity distributions that are found in the literature. The outer section had a free vortex-like distribution and the inner section had a solid body rotation. The addition of small amounts of fibers changed the tangential velocity profile significantly. The radius of solid body rotation increased, the maximum tangential velocity decreased and the transition from solid body rotation to free vortex rotation was smoothened.

Place, publisher, year, edition, pages
2005. Vol. 20, no 1, 30-35 p.
Keyword [en]
fiber suspension; hydrocyclone; measurement technique; velocity measurement
National Category
Mathematics
Identifiers
URN: urn:nbn:se:kth:diva-6375ISI: 000228457000005OAI: oai:DiVA.org:kth-6375DiVA: diva2:11069
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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