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A numerical and experimental investigation into pressure screen foil rotor hydrodynamics

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Title: A numerical and experimental investigation into pressure screen foil rotor hydrodynamics
Author: Delfel, Sean
Degree Doctor of Philosophy - PhD
Program Mechanical Engineering
Copyright Date: 2009
Publicly Available in cIRcle 2009-10-29
Abstract: Pressure screens are an effective way to remove contaminants from a pulp stream and to fractionate the pulp, or separate the fibres by length, both of which improve the quality of the end-product paper. In this thesis, seven experimental and numerical studies were conducted to investigate the hydrodynamics of pressure screen foil rotors and the effects of rotor design on the overall performance of a pressure screen. Additionally, this knowledge was applied to the development of a high performance foil rotor for both out-flow and in-flow screens. A multi-element foil rotor was developed using computational fluid dynamics (CFD), laboratory experiments, pilot plant trials, and a full scale mill trial. It was found that varying the shape and configuration of the foil affected both the pressure pulses generated by the rotor and the maximum capacity of the pressure screen. The multi-element foil (MEF) was found to be capable of generating a 126% higher magnitude negative pressure pulse, a 31% increase in screen capacity at a given rotor power consumption and a 43% reduction in power consumption without affecting capacity compared to state of the art single element rotors. The effect of varying the frequency of the pressure pulses, by changing the number of foils on the rotor, the diameter of the cylinder, and slot velocity on rotor performance was also studied. Adding foils to the rotor was found to reduce the velocity of the fluid relative to the foils and the magnitude of the pressure pulses generated by the rotors, leading to a reduction in overall screen performance. Increasing the diameter of the screen slightly reduces the performance of the foils. Increasing slot velocity did not affect the pressure pulses generated by the rotor for fully attached flows, but caused the foils to stall and a higher tip speed. Finally, factors affecting rotor power consumption other than rotor speed were investigated experimentally and analytically. The cylinder slot geometry, flow rates, and the design of the inlet to the screen were all found to have significant effects on rotor power consumption.
URI: http://hdl.handle.net/2429/14307

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