An Experimental Study of Fluid Flow in a Low Consistency Disk Refiner
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AN EXPERIMENTAL STUDY OF FLUID FLOW IN A LOW CONSISTENCY REFINER by Troy Lindsay Mithrush B.Eng. Aerospace Engineering, Carleton University, 2011 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Applied Science in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Mechanical Engineering) The University Of British Columbia (Vancouver) November 2013 c Troy Lindsay Mithrush, 2013 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 parti- cles 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 mo- tion 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. Angu- lar velocity increased proportionally with refiner speed and turnover rate did not vary significantly with refiner operating parameters. ii Preface This thesis is original, unpublished work by Troy Mithrush. The research program was proposed by Dr. James Olson and Dr. Mark Martinez. The research, including experimental design, experi- mental procedures and data analysis was performed by the author. The tracking algorithm implemented in the PPC MATLAB Image Processing and Particle Tracking Velocimetry Program was originally developed by J. Crocker, D. Grier and E. Weeks and made available in MATLAB by D. Blair and E. Dufresne. Segments of code used to condi- tion input and output data for the tracking algorithm were developed by a research colleague, J. Mackenzie. The data flow architecture, image processing, and data analysis was sole work of the author. Journal Submittals Below is a list of co-authored journal submittals. Contributions included performing compu- tational fluid dynamics (CFD) simulations, results analysis, and contributions to written content. This work is referenced in Chapter 1 and Chapter 4. 1. Rajabi Nasab, N., Mithrush, T., Olson, J.A. & Martinez, D.M. (2013), Turbulent Couette flow between two parallel corrugated walls: The case with motion of one wall perpendicular to the corrugation cavities, accepted for publication in the Canadian Journal of Chemical Engineering. This publication presents a CFD study on the flow field in the cross-section of a low consis- tency refiner. 2. Rajabi Nasab, N., Mithrush, T., Olson, J.A. & Martinez, D.M. (2013), On the relationship between plate pattern and the flow field in LC refiners: Insight into the groove depth effect and no-Load power, submitted for publication. In this publication the flow field of a low consistency refiner was investigated using CFD modelling to study the effect of groove depth on no-load power. iii Table of Contents Abstract ............................................. ii Preface ............................................. iii Table of Contents ....................................... iv List of Tables .......................................... vii List of Figures ......................................... viii Nomenclature ......................................... xii Acknowledgements ...................................... xiv 1 Introduction ........................................ 1 1.1 Working Fluid in a Low Consistency Refiner ..................... 1 1.2 Geometry and Operation of an LC Refiner ...................... 2 1.3 Fibre Treatment and The Refining Action ...................... 4 1.4 Fibre and Pulp Transport ............................... 6 1.4.1 Gross Refiner Flow .............................. 6 1.4.2 Groove Cross-sectional Flow ......................... 7 1.4.3 Fibre Capture ................................. 9 1.5 Background Review .................................. 10 1.6 Research Objectives and Thesis Organization .................... 11 2 Research Methods ..................................... 12 2.1 Experimental Methods ................................ 12 iv 2.1.1 Refining Facility ............................... 12 2.1.2 Modified Refiner Door ............................ 13 2.1.3 Experimental Setup .............................. 18 2.1.4 Experimental Test Matrix .......................... 19 2.1.5 Particle Tracking Velocimetry ........................ 22 2.2 Analysis Methods ................................... 25 2.2.1 Approach ................................... 25 2.2.2 Image Processing ............................... 26 2.2.3 Particle Tracking Algorithm ......................... 30 2.2.4 Instantaneous Velocity Measurements .................... 30 2.2.5 Lagrangian Analysis ............................. 31 2.2.6 Eulerian Analysis ............................... 31 2.2.7 Coordinate Transformations ......................... 32 2.2.8 Calibration Methods ............................. 33 2.2.9 Uncertainty Analysis ............................. 34 3 Results and Discussion ................................... 35 3.1 Qualitative Observations of Particle Behaviour .................... 35 3.1.1 Phenomenological Characterizations and Observations ........... 35 3.1.2 Qualitative Observations ........................... 39 3.2 Effect of Operating Parameters on Stator Groove Velocities ............. 45 3.2.1 Velocity Distributions at Cross-sections of Interest ............. 45 3.2.2 Axial Velocity Profile Along Stator Grooves ................. 46 3.2.3 Bulk Axial Velocity Groove Estimates versus Refiner Operating Parameters 48 3.2.4 Discussion of Stator Groove Velocity Results ................ 49 3.3 Effect of Refiner Operating Parameters on Groove Rotational Flow ......... 53 3.3.1 Results and Discussion ............................ 53 4 Conclusions and Recommendations ........................... 56 4.1 Conclusions ...................................... 56 4.2 Strengths and Limitations of Research ........................ 57 4.3 Recommendations for Future Work .......................... 57 Bibliography .......................................... 59 v A Preliminary Mechanical Design .............................. 63 A.1 Preliminary Design .................................. 63 A.2 Design Considerations for Acrylic as an Engineering Material ........... 64 A.2.1 Material Selection .............................. 64 A.2.2 Planar Disc Windows ............................. 65 A.2.3 Crazing .................................... 65 A.2.4 Water Exposure Effects ............................ 65 B Mechanical Design Drawings ............................... 66 C Structural Finite Element Analysis ............................ 76 D Industrial Operating Region Data ............................ 77 E Groove Axial Velocity Plots ................................ 79 F Fluid Transport Justification ............................... 87 vi List of Tables Table 2.1 Experimental test plan for flow rate, refiner speed and plate gap. ......... 20 Table 2.2 Summary of UV fluorescent tracer particle properties provided by Cospheric Innovations in Microtechnology. ......................... 24 Table B.1 Mechanical Design Drawing List ......................... 66 vii List of Figures Figure 1.1 LC refiner model showing important operational features including rotor and stator plates, refiner inlet and outlet, gap actuator and electric motor. ..... 2 Figure 1.2 Single disc refiner plate geometry. (a) is a frontal view of a simplified plate geometry showing the sector angle θ and the bar angle φ. (b) is the cross- sectional area of the rotor and stator plates depicting important dimensions. U is the translational velocity of the rotor over the stator at radius R in the 2D representation. .................................. 3 Figure 1.3 (a) Un-refined chemical fibres showing intact cell walls. (b) Fibrillated and collapsed chemical fibres following the refining process, reproduced with per- mission. (M Polan (1993)) ............................ 4 Figure 1.4 Gross refiner flow transport as depicted by