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J.D.Redlinger-Pohn, W.Bauer and S.Radl. Fractionation of fibre pulp in a hydrodynamic fractionation device: Influence of Reynolds number and accept flow rate. In Advances in Pulp and Paper Research, Oxford 2017, Trans. of the XVIth Fund. Res. Symp. Oxford, 2017, (W.Batchelor and D.Söderberg, eds), pp 209–228, FRC, Manchester, 2018.

Abstract

Fibre fractionation in the Hydrodynamic Fractionation Device (HDF) was studied for changing suspension flow parameters, i.e. different channel Reynolds numbers Re and accept flow rates up to 20% of the feed flow rate. The suspension flow behaviour was described using images recored with a high-speed camera system. Fractionation performance was determined based on mass balances for a variety of length fractions of the pulp. Low Reynolds number flow characterised by Re = 1300 led to the formation of a fluid gap between the wall and the fibres located at the chaneel centre. Best fractionation performance was achieved for flow at this Reynolds number: no fiber removal was observed at 10% accept flow rate, and only 1% of the fibres were removed at 20% accept flow rate. A design space was established that highlights the optimum settings for fractionation in an HDF, which at low Re and high accept flow rate. Surprisingly, we found a significant increase of fines mass flow rate in the accept upon an increase of the Reynolds number. We speculate that a flow regime-dependent interaction of fines with the fibres exists in the HDF that critically affects the amount of fines in the fluid gap near the wall.


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