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UBC Theses and Dissertations

The hydrodynamics of individual pulp fibres Wong, Tze Bun


In order to understand how pulp fibres with different properties (e.g. length, diameter, coarseness, etc.) can be fractionated in hydrocyclones, there is a need to understand the hydrodynamic behavior of individual pulp fibres. Measurements of the settling velocity of fibres in fluids of different density and viscosity can be used to give the drag coefficient of fibres as a function of the Reynolds number. Such measurements can yield Reynolds numbers up to about 0.1. In order to achieve the higher fibre Reynolds numbers present in a hydrocyclone, a novel device, called the rotating tank, was constructed to measure the velocity of fibres in water under the influence of a centrifugal field. The tank is a circular cylinder made of plexiglas, 30.5cm in diameter, and 4.45cm high, with its axis vertical. The tank is filled with fluid and is spun at a constant rate until the fluid is in solid body rotation. Fibres or other objects to be tested can be placed in the tank through a hole along the axis of the cylinder, and centrifugal forces cause the fibres to be flung outwards. A fibre inside the rotating tank is subject to a centrifugal force, a drag force, and a pressure force. The radial equation of motion of a fibre in the rotating tank will be exactly the same as during gravitational settling except the gravitational acceleration is replaced by the centrifugal acceleration. Therefore, high Reynolds numbers can be achieved by using a high rotation speed of the tank. Our rotating tank was tested and found to be capable of spinning at 1500 rpm. The tank has been primarily validated by reproducing Stokes' theory for the drag of a sphere. The tank results were in good agreement (4% error) with Stokes' theory. Further validation of the tank was done with copper wires and nylon fibres, which are similar to wood fibres. The results were in good agreement (

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