The Role Of Rheology In The Flow And Mixing Of Complex Fluids

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The Role of Rheology in the Flow and Mixing ofComplex FluidsbySara Ghorbanian Farah AbadiA thesis submitted toThe University of Birminghamfor the degree ofMASTER OF PHILOSOPHYSchool of Chemical EngineeringCollege of Engineering and Physical SciencesThe University of BirminghamNovember 2016

University of Birmingham Research Archivee-theses repositoryThis unpublished thesis/dissertation is copyright of the author and/or thirdparties. The intellectual property rights of the author or third parties in respectof this work are as defined by The Copyright Designs and Patents Act 1988 oras modified by any successor legislation.Any use made of information contained in this thesis/dissertation must be inaccordance with that legislation and must be properly acknowledged. Furtherdistribution or reproduction in any format is prohibited without the permissionof the copyright holder.

ABSTRACTMixing of fluids with complex rheology is encountered more and more frequently inindustries. Nonetheless, mixing behaviour of such fluids is still poorly understood due tothe complexity of their rheological behaviour. This study aims to enhance fundamentalunderstanding of the flow and mixing of rheologically complex fluids such as thixotropic,shear-thinning and viscoelastic fluids. The objectives of this study were to investigatewithin stirred vessels the effects of thixotropy and viscoelasticity, separately, in theabsence of other rheological behaviours for the fluids examined. To achieve these aimsthe rheological behaviour of the fluid examined is isolated by using a fluid that exhibitsonly one of these behaviours of interest at a time. The Particle Image Velocimetry (PIV)technique was employed to characterize the flow fields of fluids. The flow pattern,normalized mean velocity and cavern growth in the vessel were characterized during themixing for both thixotropic and viscoelastic fluids. The results were compared to thereference fluids under laminar and transition regimes. Three different types of impellerwere investigated: Rushton turbine (RTD), and Pitch Blade Turbine (PBT) in up pumpingmode (PBTU) and in down pumping mode (PBTD). Additional work was conductedusing th Planar Laser Induced Fluorescence (PLIF) visualization technique to investigatein more detail the evolution of mixing in a cavern with time for a thixotropic fluid. Themixing efficiency of the impellers was analyzed in terms of impeller pumping efficiencyand size and growth of a cavern.

Dedicated To My Beloved Parents

ACKNOWLEDGEMENTSFirstly, I would like to thank my supervisor Professor M. Barigou for his guidance duringthe course of my research. I would like to express my gratitude towards Professor MarkSimmons for valuable advice and support throughout this work.I would like to thank the following people: Dr. Andreas Tsoligkas for his first trainingwith PIV experiments, and Dr. Federico Alberini for his guidance in using PIV and PLIFtechniques; Dr. Asja Portsch, Dr. Taghi Miri, and Dr. James Bowen for the introductionand advice on using a Rheometer; Dr. Hamed Rowshandel for his valuable advice inMatlab, and Dr. Halina Murasiewicz and Dr.Artur Majewski for their generous supportthrough this research.In addition, I would like to express my appreciation, for their valuable help concerningthe experimental setup, to David Boylin, Thomas Eddleston and Steven Williams fromthe workshop team.I would also like to thank all the great people from the General Office, especially LynnDraper, for their friendship and continuous support. I want to thank Zainab Alsharify,Shahad Al-Najjar Dr. Li Liu for their friendship and support.I have to also thank the student services team, especially Julie Kendall and Laura Salkeld,for their understanding and support.Last but not least, I would like to thank my family: my beloved parents, lovely sister,supportive brother, and sweet grandmother for their encouragement and infiniteunderstanding and support. I have to also thank my husband for his understanding andsupports.

TABLE OF CONTENTSChapter 1: INTRODUCTION . 11.1 Motivation. 11.2 Objectives . 31.3 Thesis layout . 4Chapter 2: LITERATURE REVIEW . 52.1 Mixing Systems . 52.1.12.1.2Mechanically Agitated Vessels . 6Flow Regime . 72.1.2.12.1.2.22.1.32.1.42.1.5Laminar and Transitional Flow Regimes . 9Turbulent Regime. 11Impeller selection and resulting flow patterns . 12Unconventional Geometry . 18Mixing Times . 192.2 Fluid Rheology . 212.1.12.2.12.2.22.1.2Newtonian and non-Newtonian Fluids. 21Viscoelastic Fluid . 23Viscoplastic Fluid . 26Thixotropic Fluid . 282.3 Visualization Techniques. 302.3.12.3.22.3.32.3.42.3.5Hot Wire Anemometry (HWA) . 31Laser Doppler Velocimetry/Anemometry (LDV/A) . 32Planar laser Induced Fluorescence (PLIF) . 34Particle Image Velocimetry (PIV) . 35Positron Emission Particle Tracking (PEPT) . 37Chapter 3: EXPERIMENTAL TECHNIQUE AND THEORETICAL ANALYSIS . 403.1 Apparatus . 403.2 Particle Image Velocimetry (PIV) . 433.3 Planar Laser Induced Fluorescence (PLIF) . 453.4 Flow Number . 47Chapter 4: EFFECT OF THIXOTROPY ON FLUID MIXING IN A STIRRED TANK . 504.1 Introduction. 514.2 Material and Experimental Design . 534.2.1Rheology of Test Fluids . 534.2.1.14.2.1.24.2.2Rheology Results . 544.2.2.14.2.2.24.2.34.2.4Time Dependent Fluids (Thixotropy) . 53Time Independent Fluids. 54Hysteresis Loop Test . 56Steady State Shear Viscosity. 57Experimental Design . 61Experimental Techniques . 61

4.3 Results and Discussion . 624.3.1Flow Fields. 634.3.1.14.3.1.24.3.1.34.3.24.3.3Re 158 . 63Re 61 . 72Re 7 . 72Cavern Growth . 76Effect of Non-standard Configurations . 804.3.3.1 Un-baffled Vessel. 804.3.3.2 Off-bottom Clearance Effects . 894.4 Conclusions . 94Chapter 5: THE EFFECT OF VISCOELASTICITY IN A STIRRED TANK . 975.1 Introduction. 975.2 Rheology and Material Characterization . 1005.2.1Test fluids . 1005.2.1.15.2.1.25.2.1.35.2.2Viscoelastic Fluid (Boger Fluid) . 100Newtonian Fluid . 101Shear-thinning Inelastic Fluid . 101Rheology of Test Fluids . 1025.3 Experimental Setup. 1085.4 Results and Discussion . 1085.4.1Newtonian Fluid (N93, N95) . 1095.4.1.15.4.1.25.4.1.35.4.1.45.4.2Low viscoelastic Boger Fluids (100PAA) . 1165.4.2.15.4.2.25.4.2.35.4.35.4.45.4.5Re 80 . 109Re 45 . 113Re 7 . 114Shear-thinning Inelastic Fluid . 115RTD Configuration . 116PBTU Configuration . 119PBTD Configuration . 122High viscoelastic Boger Fluid (300PAA) . 123Pseudo-Caverns . 128Conclusions . 129Chapter 6: CONCLUSIONS AND FUTURE WORK. 1316.1 Conclusions . 1316.2 Future work . 133REFERENCES . 135

LIST OF FIGURESFigure 2.1. Schematic representation of a typical mechanically agitated vessel (Edwardset al., 1997). 7Figure 2.2. Typical predicted 2D flow patterns for a fully baffled vessel with (a) axialflow and (b) radial flow impeller (Edwards et al., 1997). . 13Figure 2.3. Schematic illustration of 2D flow patterns around a radial flow impeller in aviscoelastic fluid, (a) low EI, (b) intermediate EI, (c) high EI (Özcan-Taskin and Nienow,1995) . 15Figure 2.4. (a) Three-blade propeller, (b) Six-blade disc turbine, (c) Simple paddle, (d)Anchor impeller and (e) Helical ribbon (Edwards et al., 1997). . 17Figure 2.5. Mixing time measurement (Edwards et al., 1997) . 20Figure 2.6. Rheological properties of Newtonian and non-Newtonian fluids (Paul et al.,2004) . 22Figure 2.7. Stress components around a rotating coaxial cylinder (Özcan-Taskin, 1993). 24Figure 2.8. Breakdown of a 3D thixotropic structure (Barnes, 1997) . 30Figure 2.9. A typical LDV experimental set up, 1: laser; 2: fiber-optical module; 3:transmitting/receiving optics; 4: stirred vessel; 5: photomultipliers; 6: flow velocityanalyser; 7: oscilloscope; 8: computer; 9: intersection of the two laser beams (Guida,2010) . 32Figure 2.10. Simplified PLIF experimental facility. . 35Figure 2.11. Simplified, typical PIV set-up, Image taken from (Guida, 2010). 36Figure 2.12. Schematic illustration of a PEPT experimental set-up showing positronannihilation and 𝛾-ray detection by the PEPT camera, Image taken from (Guida, 2010). 38Figure 3.1. The layout of the stirred vessel configurations, equipped with impeller, asused in this work. (a) baffled, (b) un-baffled. . 41

Figure 3.2. Impeller geometries used in the experiments, a) PBT, b) RTD . 42Figure 3.3. Schematic of various off-bottom clearance configurations studied in this work. 43Figure 3.4. Experimental setup for PIV measurements . 44Figure 3.5. Pixel greyscale versus tracer concentration . 46Figure 3.6. Experiment setup for PLIF experiments . 46Figure 3.7. Schematic diagram of flow rates for PBTD impeller taken from (Guida et al.,2010). . 48Figure 4.1. 2.2w% Laponite fluid under application of shearing followed by arecoveryperiod for three different shear rates . 55Figure 4.2. Viscosity curve overlap in test runs. . 56Figure 4.3. (a) Full shear ramp experiment of 2.2w% Laponite fluid (six ramps), . 58Figure 4.4. Schematic of steady shear flow tests; (a) few constant shear stress applied tothe thixotropic fluid (b) response of shear rate at constant shear stress over a time ofexperiments. . 59Figure 4.5. Flow curves corresponding to different shearing times of 2.2w% Laponite. 59Figure 4.6. Flow curve of 1w% Carbopol fluid at different shearing times. . 60Figure 4.7. The contour of normalized velocity magnitude of three impellers for 2.2w%Laponite at Re 158. . 65Figure 4.8. Velocity vector on an axial-radial plane for a two flow regime at Re 61 andRe 158 for both fluids mixed by the PBTD impeller. . 66Figure 4.9. The contour of normalized magnitude velocity for the three impellers at . 68Figure 4.10. Velocity vector on an axial-radial plane for two flow regimes Re 61, Re 158 for both fluids mixed with the PBTU impeller. . 69

Figure 4.11. Contour of shear strain rate plot for 2.2w% Laponite (at t1 and t3) and 1w%Carbopol fluid. . 71Figure 4.12. The contour of normalized magnitude velocity for three impellers for2.2w% Laponite at Re 61. . 73Figure 4.13. (a) Normalized magnitude velocity for three impellers at Re 7 for 2.2w%Laponite fluid at t3, (b) velocity field for three impellers at Re 7 for 2.2w% Laponitefluid at t3. . 75Figure 4.14. The changes of normalized cavern area % for the thixotropic fluid as afunction of time for (a) Re 158 and (b) Re 61. . 76Figure 4.15. The cavern height and radius growth as a function of time for the thixotropicfluid at (a) Re 158, (b) Re 61. . 77Figure 4.16. Schematic diagram of cavern growth while mixing for 2.2w% Laponite and1w% Carbopol at Re 61. . 78Figure 4.17. The cavern growth from PLIF experiments for both 1w% Carbopol and2.2w% Laponite fluid at Re 7. 79Figure 4.18. Variation of Power number as a function of Reynold number for viscoplasticfluid in the (a) baffled vessel and (b) un-baffled vessel. Image adopted from Hirata andAoshima (1996). . 81Figure 4.19. The cavern shape and size for the thixotropic and viscoplastic fluids in thebaffled and un-baffled vessel at Re 158. . 82Figure 4.20. The contour of

Mixing of fluids with complex rheology is encountered more and more frequently in industries. Nonetheless, mixing behaviour of such fluids is still poorly understood due to the complexity of their rheological behaviour. This study aims to enhance fundamental understanding of the flow and mixing of rheologically complex fluids such as thixotropic,

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