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Study of hydrodynamic cavitation by CFD modeling

Study of hydrodynamic cavitation by CFD modeling. Chemical and Materials Engineering University of Alberta. Outline. Background M ilestone Cavitation modeling Cavitation experiments Future work. Background.

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Study of hydrodynamic cavitation by CFD modeling

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  1. Study of hydrodynamic cavitation by CFD modeling Chemical and Materials Engineering University of Alberta

  2. Outline • Background • Milestone • Cavitation modeling • Cavitation experiments • Future work

  3. Background • Objective: develop a system for enhancing fine particle flotation using microbubbles generated by cavitation • Mechanism proposed by Zhou et al. 1997 • Hydrophobic particle surface in water is a good nucleation sites for cavity generation particle particle tiny bubble tiny bubble Flotation-sized bubbles Enhanced coagulation by Bubble bridging Two stage attachment

  4. Milestone • Develop a model for cavitation using CFD • Apply the cavitation model in a high intensity agitation system • Determine critical variables for hydrodynamic cavitation • Determine bubble size distribution using population balance equations • Measure bubble size distribution • Couple the cavitation and population balance equations with flow equations • Study floatation recovery

  5. HIA Cell CFD modelling CFD Modelling of cavitation is performed for the laboratory HIA cell for different impeller speeds and different dissolved gas content.

  6. Volume fraction of vapor Contours of pressure and volume fraction of vapor in the HIA cell Pressure

  7. Geometries • Orifice (R/r=2,3, R=2cm) • Venturi (R/r=2, R=2cm) • Contraction (R/r=2, R=2cm) R r R r R r

  8. Pressure profile in venturi Our model Hu et al. 1998 • Minimum inlet velocity is 4 m/s for the studied venturi

  9. Pressure and velocity profiles in venturi Single phase model Inlet velocity=4m/s Pressure profile (Pa) Velocity profile (m/s)

  10. Pressure profiles in orifice Single phase model Inlet velocity=4m/s

  11. 2D and 3D comparison Single phase model Inlet velocity=4m/s 2D 3D

  12. Cavitation models • Schnerr-Sauer model • Bubble number density • Zwart-Gerber-Belamri • Bubble diameter • Evaporation coefficient • Condensation coefficient • Singhal et al. cavitation model • Non-condensable gas fraction

  13. Cavitation modelling • Multiphase flow • Continuity equation for mixture • Momentum equation for mixture • Cavitation model for vapor phase • Bubble dynamics: growth of cavitation bubbles using Rayleigh-Plesset equation

  14. Cavitation model • vapor transport equation Evaporation rate term Condensation rate term When Pv ≥ P When Pv ≤ P Singhal et al. (2002): Ce=0.02, Cc=0.01

  15. Multiphase modelling in orifice • Continuity, turbulent flow model and Singhal et al. cavitation model, inlet velocity: 4m/s

  16. Multiphase modelling in orifice • Singhalet al. and Zwart-Gelber-Belamri Cavitation models (inlet velocity=4 m/s)

  17. Multiphase modelling in orifice • Continuity, turbulent flow model and Singhal et al. cavitation model, inlet velocity: 4m/s and 4.5m/s

  18. CFD analysis in orifice R/r=3 • Velocity contours in orifice (R/r=3) • Pressure profile • vapor fraction contours Inlet velocity= 4 m/s Max velocity= 51 m/s Max pressure= 1.14 MPa Min pressure= -98 kPa Max vapor fraction= 0.92 Cavitation model: Zwart-Gerber-Belamri

  19. 3D Multiphase modelling in orifice

  20. Experimental Setup

  21. Experimental Setup • ID= 1 inch • Variable speed slurry pump • Velocity range: 0-6 m/s for 1 inch ID tube

  22. Proposed setup • Pump: • Centrifugal • Max flow: 66 GPM • Max head: 122 ft • Price: $ 2000 • Flowmeter • Coriolis Flow and Density Meter

  23. Gas holdup measurements • FBRM • 0.8 to 1000 micron • Inline detection • CCD • RedlakeMotionscope • 517 fps @ 1280 x 1024 • Min exposure time 1µs R. J. N. Bernier, “Unsteady two-phase flow instrumentation and measurement,” Ph.D. dissertation, Cal.. Inst. Technol., Pasadena, 1982.

  24. Gas holdup measurements • Acoustic spectrometer • Sonartrac • 2”-36” • 1-10 m/s • 1-20 % • 5 % accuracy • $ 16500 R. J. N. Bernier, “Unsteady two-phase flow instrumentation and measurement,” Ph.D. dissertation, Cal.. Inst. Technol., Pasadena, 1982.

  25. Gas holdup measurements • Conductivity cell: C: Specific conductivity of the solution G: Measured conductivity of the solution L: Distance between two plates A: area of the plates L/A: cell constant http://www.coleparmer.ca/techinfo/techinfo.asp?htmlfile=Conductivity.htm&ID=78

  26. Gas holdup measurements • Electrods: • Coaxial • Parallel flat plate • Wire grid http://www.coleparmer.ca/techinfo/techinfo.asp?htmlfile=Conductivity.htm&ID=78

  27. Future Work Implement physical experiments to evaluate parameters in cavitation model and population balance model Use UDF in Fluent to model the generation of bubbles Implement the population balance in a bubble-particle environment Determine bubble-particle and particle-particle collision rate (frequency) and efficiency model parameters {experiments} Develop comprehensive model for flotation involving in-situ bubble generation, bubble-particle interaction and the ultimate flotation recovery. Study the effect design and operating parameters on fine particle flotation

  28. Acknowledgements • Financial support for this work from: • NSERC-CAMIRO CRD Grant on Fine ParticleFlotation • NSERC-industrial Research Chair Program in Oil Sands Engineering.

  29. Thank you for your attention

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