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An experimental study of fluid flow in a low consistency refiner Mithrush, Troy Lindsay

Abstract

Transport phenomena inside a low consistency disc refiner were experimentally investigated. A transparent refiner door was designed and fabricated with four acrylic viewports enabling plate-scale and groove-scale visual observation. High speed video, ultra-violet fluorescent tracer particles and a MATLAB program were used to perform particle tracking velocimetry to gain further understanding of the flow field. The experimental working fluid under study was water. The effects of refiner operating parameters on the flow field were of particular interest. Refiner flow rates were varied from 300 to 700 litres per minute. Refiner rotational speeds were varied from 400 to 1200 RPM. Plate gap values under study included 7.5, 2.5, 1.5, and 0.75 mm. Two plate configurations were studied, including a smooth rotor and grooved rotor with a machined acrylic stator plate. The plate geometry under test was designed for softwood pulp having a bar edge length equal to 0.99 km/rev. A set of phenomenological characterizations of observed particle behaviour was identified. Qualitative results were provided for the effect of gap, refiner speed, and flow rate on the flow field. Lagrangian pathlines were shown to reveal tortuous flow for grooved rotor experiments. Quantitative results were presented for grooved rotor experiments for gaps of 0.75 mm. Eulerian measurements of groove axial velocity indicated fluid transport into and out of the stator grooves, while net transport occurred out of the grooves. The presence of backflow in the stator grooves was observed at all operating points for the grooved rotor under test. The relationship between stator backflow velocity and operating parameters was reported showing an increase with refiner speed and a minimal decrease with refiner flow rate. It has been shown that there is a linear relationship between stator backflow velocities and the pressure differential across the refiner. Rotational motion in the stator grooves was quantified by angular velocity and turnover rate of the fluid. Turnover rate was defined as the number of rotations of the fluid as it travels the length of the groove. Angular velocity increased proportionally with refiner speed and turnover rate did not vary significantly with refiner operating parameters.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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