University of Alberta Characteristics of the Vortex Structure in the Outlet of a Stairmand Cyclone: Regular Frequencies and Reverse Flow Mei Chen O A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirernents for the degree of Master of Science in Chemical Engineering Department of Chemical and Materials Engineering Edmonton, Alberta FaIl 1999 National Library Bibliothèque nationale I*$1Iof Canada du Canada Acquisitions and Acquisitions et Bibliographie Services senrices bibliographiques 395 Wellington Street 395. rue Wellington OttawaON K1AON4 OttawaON K1AON4 Canada Canada The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant a la National Library of Canada to Bibliothèque nationale du Canada de reproduce, Loan, distribute or sel1 reproduire, prêter, distribuer ou copies of this thesis in rnicrofom, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/filrn, de reproduction sur papier ou sur format électronique. The author retains ownershp of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or othenvise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. To my diligent and sacrificial parents To whom 1 owe al1 that I am Abstract In this project. a combination of experiments and simulations is used to investigate the penetration of the processing vortex core into the cyclone, the extent of the reverse flow, and the impact of the geometry on the flow field. Periodic motions were detected in the gas outlet tube or just outside of the gas outlet tube with the three gas outlet tube diameters tested. The observed oscillations are caused by a coherent structure. These oscillations grow less vigorous down the gas outlet tube and eventually die out. Time avenged axial velocity profiles at different elevations indicate that the back flow region shrinks down the gas outlet tube. Numerical simulation (3D)was also conducted. With the Reynolds Stress Mode1 (RSM) to account for the non-isotropie effect of turbulence in the highly swirling tlow, the CFD simulation prove to be effective in capturing the essential features of the flow in cyclone. Acknowledgments 1 must begin by acknowledging Professor Kresta and Professor Mees, who were excellent instructors, motivators and overseers of the project. In addition, ail my colleagues in our group gave me much help. Dr. Bara and Dr. Hackman at Syncmde Canada are thanked for their much insightful advice. To the list 1 must add the personnel in the machine shop. DACS center and the instrument shop. for their hard work. The financial aid for this project was graciously provided by Syncmde Canada Ltd. Table of Contents Chapter 1 : Introduction ............................................................................... 1 1.1 The fùnction of a cyclone ...................................................................... 1 1.2 Geometric variables of a cyclone .......................................................... 1 1.3 General flow pattern in a cyclone ....................................................... 1 1.4 The mechanism of particle separation ................................................... ,7 . 1.5 Previous investigattons .......................................................................... 3 1 .5 . 1 Experimental work ........................................................................... 3 1 .5 .1.1 Back flow in the center of the core .................................. ., ...... 3 1 .5 .1.2 Flow oscillation in cyclone ........................................................... 5 1S.2 Numerical work ............................................................................... 8 1.6 Approach used in this work ................................................................. 10 Chapter 2: Experimental ............................................................................ 17 2.1 The principle of laser Doppler anemometry (LDA) - an overview.... 17 2.2 Optical system.................................................................................... 19 2.2.1 Optical configurations ................................................................... 19 2.2.2 Optical requirements and cornponent measured in the study........ 20 2.3 Seeding design (seeding tank) ............................................................ 21 2.4 Cyclone mode1 and blower .................................................................. 24 2.4.1 Cyclone mode1 .................................... .................................... 24 2.4.2 Blower ............................................................................................25 2.5 Cyclone alignment .............................................................................. 26 2.6 Experiment error prediction and equipment calibration ..................... 27 2.7 Conclusion ...........................................................................................28 Reference .................................................................................................. 3 8 Chapter 3: Experimental results ............................................................... 39 3.1 Data analysis technique ................................................................ 39 3.1.1 Alias fiee sampling ........................................................................ 39 3.1.2 Turbulence power spectrum ......................................................... 40 3.1.3 Transformation to fiequency domain using FFT........................... 40 3.1.4 Autocorrelation Function ............................................................... 42 3.1.5 Analyzing unevenly spaced data ................................................. 42 3.2 Flow field rneasurements .................................................................. 44 3.2.1 Inlet velocity................................................................................... 44 3.2.2 Axial velocity ................................................................................. 45 3.2.3 Tangential velocity..................................................................... 49 3.2.4 Measurements at different inlet velocities..................................... 51 3.2.5 Measurements at different gas outlet tube diameters ..................... 51 3.3 Discussion ............................................................................................ 52 3.3.1 The mechanisrn of back flow ......................................................... 52 3.3.2 Origin of coherent stmcture and asymmetric flow tiled ............... 54 3.3.3 Volumetric flow rate ..................................................................... 54 3.3.4 Momentum balance ....................................................................... 55 3.4 Conclusions .......................................................................................... 56 Re ferences :................................................................................................. 88 Chapter 4 Characterization of swirling flows in cyclone using dimensional analysis ................................................................................... 90 4.1 Dimensional anal y sis..................................................................... 90 .. 4.1.1 Buckingham s Pi theorern ............................................................ 90 4.1.2 Nondimensional parameter determined fiom differential equations . ............................................................................................................... 92 4.2 Swirl number ........................................................................................ 94 4.2.1 Generation of swirl and calculation of swirl number .................... 97 4.3 Strouhal number................................................................................... 97 4.4 Results ........................... ... ..........*.....................................-.........*......*..99 Reference: ................................................................................................ 1 03 Chapter 5: Computational Techniques ................................................ 1 5.1 Introduction ........................................................................... 104 5.2 Computational Fluid Dynamics Soiver FLUENT.......................... 104 5.2.1 Mathematical Formulation .................................................... 1 04 5.2.2 Turbulence Models............................................................... 1 06 5.2.3 Computational domain. boundary conditions and time step.... 108 5.2 Validation of CFD results ......................................................... 1 11 5.3 Numerical results versus experirnental results ............................... 1 12 5.4 Prediction of the frequency of oscillation................................... 1 13 5.4.1 Tirne averaged velocity prediction ........................... ... ........... 1 14 ... 5.4.2 Solution sensitivity.................................................................... 1 15 5.5 Possible reasons for the discrepancy between experiment and simulation...................................................................................... 1 15 5.6 Conclusion:..................................................................................