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CVEN 679 Term Project Presentation

CVEN 679 Term Project Presentation. Multiphase Flow studies using PIV. Collaborators: CHAMPA JOSHI TIRTHARAJ BHAUMIK RAMAKRISHNAN HARI PRASAD. PROJECT OBJECTIVE

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CVEN 679 Term Project Presentation

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  1. CVEN 679 Term Project Presentation Multiphase Flow studies using PIV Collaborators: CHAMPA JOSHI TIRTHARAJ BHAUMIK RAMAKRISHNAN HARI PRASAD

  2. PROJECT OBJECTIVE The PIV (Particle Image Velocimetry) measurement method is used to obtain relevant parameters in the study of multiphase plumes with the objective of validating numerical models and use them to predict field phenomena.

  3. MULTIPHASE FLOW BASICS Multiphase flows are fluid flows involving the dynamics of more than one phase or constituent • One of the core areas of research inEnvironmental Fluid Mechanics • Dispersed & Continuous Phases Dispersed Phase : Bubbles, Droplets, Powder Continuous Phase : Water, Air • Jets: Driving force – Momentum flux of dispersed phase • Plumes: Driving force – Buoyancy flux of dispersed phase

  4. Applications • Bubble Breakwaters • Antifreeze measures in Harbors • Bubble curtains for Oil spill containment • CO2 Sequestration in Ocean • Lake Aeration • Reservoir Destratification

  5. SCHEMATIC OF A SIMPLE AIR-BUBBLE PLUME Bubbles Bubbles (Dispersed Phase) Water (Continuous phase)

  6. MULTIPHASE PLUMES IN STRATIFIED ENVIRONMENT N=((-g/ρr)*(dρa/dz))1/2 hP LIF Image of a Type 3 plume

  7. Dimensional Analysis: 0 0 0 hT = f (Qinit , Minit , Bb_init , Bw_init , us , N , HT ) ∏1 = hT / (B/N3)¼ ∏2 = us / (BN)¼ ∏1 = g ( ∏2 ) Total no. of variables = 4 Total no. of dimensions = 2 (L, T) BUCKINGHAM-PI THEOREM (4 – 2) = 2 non-dimensional groups ∏1 : Non-dimensional Trap Height ∏2 : Non-dimensional Bubble Slip Velocity

  8. Relationship between the non-dimensional parameters validated from experiments: Single-phase plumes: ∏1 = 2.8 Two-phase plumes: ∏1 = 2.8 – 0.27∏2 ∏1 = 5.2exp(-(П2 – 1.8)2/10.1)

  9. Field Scale Complications: • Stratification profile may be non-linear - N varies with depth • There may be bubble expansion - us varies with depth • There may be more than one dispersed phases present LEADS TO: Poor correlation between lab and field scales! REMEDY: Numerical models with parameters validated from laboratory experiments can include the field-scale complications

  10. Governing Differential Equations: • Conservation of Mass flux • Conservation of Momentum flux • Conservation of Buoyancy flux of dispersed phase • Conservation of Buoyancy flux of continuous phase Unknown parameters to be solved: Um–velocity of continuous phase 2b – width of plume Cm – void fraction of dispersed phase g’ – reduced gravity of continuous phase

  11. Gaussian and Top-Hat profiles: SELF – SIMILARITY ASSUMPTION Top-Hat Distribution Gaussian Distribution X: state variable of interest ( u, C, ∆ρ)

  12. Derivation of the Governing Equations: 2b Entrainment Hypothesis Balance of buoyant forces on two phases Viscous Drag is negligible for water Momentum of air bubbles is negligible Dilute plume assumption Density locally invariant inside C.V

  13. Numerical models: Mixed-fluid model : McDougall (1978), Asaeda & Imberger (1993) - Treats the dispersed and continuous phases as a single mixture Two-fluid model : Socolofsky & Adams (2001) - Treats the dispersed and continuous phases as separate entities

  14. Numerical Model Equations: NUMERICAL SCHEME USED: 4TH ORDER RUNGE-KUTTA

  15. Critical Model Issues: • Entrainment Coefficient • Initial conditions Um , b and alpha are to be estimated using PIV measurements

  16. Particle Image Velocimetry

  17. Facilities & Equipments • Experimental Tank (40 x 40 x 70 cm) made of transparent acrylic glass (Plexiglas) • Diffuser source (Airstone - 1.4 cm dia) – produces bubbles of 3 mm dia above Q = 0.25 l/min • Electronic Mass Flowmeter (Aalborg GFM 171) and Needle valve • 3.2 mm piping • Laser Light Source: (Nd:YAG pulse laser) -Maximum power(400 mJ/pulse) - Wavelength (532 nm - green) - Pulse width ( 8 nanoseconds) - Time interval between pulses ( 4 ms ) - Thickness of laser light sheet (4 mm) • Optics - Cylindrical Lens – creates planar light sheet • Seeding Particles – Polyamide spheres (white, 50 μm diameter) • Camera (CCD) – Flowmaster 3S (3) - Frame rate (8 fps) - PixelResolution (1280 x 1024) - Grayscale Resolution (12-bit : 0 to 4095 grayscales) - Field of View (18cm x 18 cm for each of the 3 cameras) - Controllable exposure time (0.2 to 125 ms) • Computer - Data analysis software – DaVis (product of LaVision GmBH) - Synchronization unit – controls timing of laser pulse triggering and camera exposure - Frame Grabber – captures frames and transfers to computer RAM and then to Hard Disk - Utilities – Matlab

  18. PIV EXPERIMENTAL SETUP

  19. MEDIAN FILTERING FOR PIV DATA Interrogation Window – 16 X 16 pixels, 50% overlap UMEDIAN – 1.5URMS < U < UMEDIAN + 1.5URMS

  20. PTV ANALYSIS BY THRESHOLD Grayscale intensity Threshold Range for a 12-bit CCD camera: 0 – 4095 Intensity Threshold for the brighter bubbles: 2500

  21. FLUID & BUBBLE VELOCITY PROFILES Fluid velocity profile: Resembles Gaussian Bubble velocity profile: Resembles Top-Hat

  22. ENTRAINMENT COEFFICIENT FROM PIV IMPORTANT FINDING: Alpha is not constant and varies non-linearly with depth

  23. COMPARISON W/TWO-FLUID MODEL Model and experimental results agree appreciably well

  24. COMPARISON W/MIXED-FLUID MODEL Model overpredicts the velocity of continuous phase and the momentum flux

  25. RESULTS: • PIV of unstratified bubble plume successful • Entrainment coefficient depends on bubble concentration • Two-fluid models appear to match plume physics better than mixed fluid models ONGOING WORK: • Combining three different FOV to get better aligned data • Application of PIV to stratified bubble plume • Extending single plume numerical model to double plume • Obtaining appropriate initial conditions FUTURE SCOPE OF WORK: • PIV-LIF Combined study for the bubble plume • Develop LES (Large Eddy Simulation) numerical models

  26. REAL-LIFE SCENARIOS: • Ocean Sequestration of Liquid CO2(constitutes 64% of global greenhouse gas emissions)

  27. Other Applications: • Aeration of Lake/Aquariums • Fate of oil/chemicals released in deep sea due to accidental leakages and blowouts • Bio-medical Engineering - blood flow modeling in a ventricular assist device • Chemical industries - two-phase flow modeling due to countercurrent chromatography • Metallurgy -gas stirring of molten metals in ladles, in nuclear devices and chemical reactors

  28. References: • Asaeda, T. & Imberger, J. (1993), ‘Structure of bubble plumes in linearly stratified environments’, J.Fluid Mech.249, 35-57. • Bergmann C. (2004), ‘Physical and Numerical studies on multiphase plumes’, MS Thesis, Dept. of Civil Engrg,, Coastal & Ocean Engrg. Program, Texas A&M University, College Station, TX. • Bergmann C., Seol D.-G., Bhaumik T. & Socolofsky S. A. (2004), ‘Entrainment and mixing properties of a simple bubble plume’, Abstract # 272, 4th International Symposium on Environmental Hydraulics, IAHR, Hong Kong, China. • Lemckert, C. J. & Imberger, J. (1993), ‘Energetic bubble plumes in arbitrary stratification’, J.Hydraulic Engrg..119(6), 680-703. • McDougall, T.J. (1978), ‘Bubble plumes in stratified environments’, J.Fluid Mech.85(4), 655-672. • Milgram, J.H. (1983), ‘Mean flow in round bubble plumes’, J.Fluid Mech.133, 345-376. • Morton, B. R., Taylor, S. G. I. & Turner, J. S. (1956), ‘Turbulent gravitational convection from maintained and instantaneous sources’, Proc. of the Royal Soc.A234, 1-23 • Schladow, S. G.(1993), ‘Lake destratification by bubble-plume systems: Design methodology’, J. Hydr. Engrg.119(3), 350-368. • Socolofsky S. A. (2001), ‘Laboratory Experiments of Multi-phase plumes in Stratification and Crossflow’, Ph.D Thesis, Dept. of Civ. Env. Engrg., MIT, Cambridge, MA. • Socolofsky, S. A., Crounse, B. C. & Adams, E. E (2002), ‘Multi-phase plumes in uniform, stratified and flowing environments, in H. Shen, A. Cheng, K.-H. Wang & M. H. teng, eds, ‘Environmental Fluid Mechanics – Theories and Applications’, ASCE/Fluids Committee, Chapter 4, pp. 84-125. • Wuest, A., Brooks, N. H. & Imboden, D. M. (1992), ‘Bubble plume modeling for lake restoration’, Water Resour. Res.28(12), 3235-3250. Related Links: • http://vtchl.uiuc.edu/basic/r/bp/ • http://www.dantecdynamics.com/PIV/System/Index.html • http://archive.greenpeace.org/politics/co2/co2dump.pdf • www.umanitoba.ca/institutes/fisheries/eutro.html • http://bss.sfsu.edu/ehines/geog646/Marine%20Pollution.pdf • http://www.sealifesupply.com/aquaria.htm

  29. Questions ?

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