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TUSTP 2003

TUSTP 2003. Mechanistic Modeling and CFD Simulations of Oil-Water Dispersions in Separation Components. by Carlos F. Torres May 20, 2003. Topics. Background Objectives Particle Tracking Model Preliminary Results Universal Dispersion Model. Background.

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TUSTP 2003

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  1. TUSTP 2003 Mechanistic Modeling and CFD Simulations of Oil-Water Dispersions in Separation Components by Carlos F. Torres May 20, 2003

  2. Topics • Background • Objectives • Particle Tracking Model • Preliminary Results • Universal Dispersion Model

  3. Background • Knowledge of particle motion and phase distribution will enhance performance evaluation of separation equipment • TUSTP has used the Eulerian-Lagrangian technique to design and analyze performance of separation devices such as GLCC, LLCC and LLHC • Existing models carry out simulations considering mainly the following forces acting on a particle: drag and buoyancy • Additionally, these models assume particle local equilibrium

  4. Objectives • The general objectives of this study are to develop models capable of characterizing hydrodynamics of multiphase dispersion flow in separations and piping components • Initially, study focuses on dilute and dense dispersed flow • Develop a mechanistic model for calculating droplet motion, considering the different acting forces • Determine dispersed phase void fraction • Validate and extend the three way coupling approach proposed by Gomez 2001

  5. Particle Tracking Model • General approach • Simplified approach • Future improvements

  6. Particle Tracking:General Approach • Gomez 2001 presented a new Eulerian – Lagrangian mechanistic model: • Local equilibrium assumed for dispersed phase • Forces used: drag, lift, body force, added mass and pressure gradient • Model is one way coupling between continuous and dispersed phase, considering variation of interfacial area

  7. Lagrangian Equation • Forces on particle • Effects of continuous phase turbulence on particle: • Behzadi et al (2001) presented an averaging approach for the effects of fluid turbulence on particles • Iliopoulos et al. (2003) presented a stochastic model for the effects of turbulence in dispersed flow

  8. Particle Tracking:Simplified Approach • Modifications of Gomez model (2001): • Forces considered: drag, lift and body force • Main goal is calculation of particle trajectory • Parametric technique (function of time) allows determination of particle’s residence time (integration 2nd order accuracy) • Particles are spherical and non-deformable, particle to particle interaction not considered (dilute dispersion) • One way coupling • 3D solution developed for Cartesian and Cylindrical coordinate systems

  9. Modified Gomez Model • Forces on Particle • Particle Position

  10. Particle Tracking:Future Improvements • Extend model capability to include: • Added mass force • Pressure gradient force (hydrodynamic) • Fluid turbulent effects • Particle transients effect • Develop mechanistic model for estimation of void fraction using stochastic approach • Explore limits of dilute flow assumption, and extend to dense flow

  11. Preliminary Results • Particle Tracking in Pipe Flow • Particle Tracking in Stratified Flow • Particle Tracking in Conventional Separators

  12. Particle Tracking: Pipe Flow Mixing Length Velocity Profile

  13. Particle Tracking:Pipe Flow  = 0o, d = 5in, Vcont = 0.01 m/s. Water Continuous (1000 kg/m3, 1cp). Dispersed phase Oil (850 kg/m3), dp = 100 microns

  14. Particle Tracking: Stratified Flow  = 0o, d = 3in, Uls = 0.1 m/s, Ugs = 1.0 m/s Air Water system at 25 C and 1 atm. Shoham and Taitel (1984)

  15. Particle Tracking:Conventional Separators

  16. Particle Tracking:Conventional Separators

  17. Particle Tracking: Conventional Separators Particle Residence Time = 2.63 s Particle Density = 2500 kg/m3 Particle Diameter = 500 micron

  18. Particle Tracking: Conventional Separators Particle Residence Time = 2.362 s Particle Density = 2500 kg/m3 Particle Diameter = 500 micron

  19. Universal Dispersion Model • Gomez Model (2001) • The Eulerian field is known (average velocities, turbulent kinetic energy and energy dissipation) • Solve Lagrangian field using the proposed equation, to calculate slip velocity within flow field • Solve diffusion equation using slip velocity information, to predict void fraction distribution • Calculate bubble or droplet diameter using Eulerian turbulent quantities and void fraction distribution • Repeat non-linear process until convergence is reached

  20. Phase Coupling Model • Definition of Phase Coupling • One-way Coupling: Fluid flow affects particle while there is no reverse effect. • Two-way Coupling: fluid flow affects particle and vice versa. • Four-way Coupling: Additionally from above, there are hydrodynamic interactions between particles, and turbulent particle collisions. • Three-way Coupling

  21. Phase Coupling Model • Continuous phase momentum equation (N- S Equation) • Dispersed phase momentum equation (average) • Particle Source Term, MPso is estimated by coupling mass and momentum balances over control volume.

  22. Two-way Coupling: Solution Scheme • PSI – Cell technique, Crowe et al. (1977) Huber & Sommerfelt (1997). Air continuous Phase.  = 0o, d = 80 mm, V = 24 m/s, Dispersed phase d = 2500 kg/m3 dp = 40 micron

  23. Model Potential LLCC Dispersion of Oil in Water with Water Layer at the Bottom Vm = 0.6 m/s W.C = 67%

  24. Questions ? ? ? ?

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