Fluent多相流模拟 Multiphase Flow Modeling.ppt

Agenda Introduction Modeling Free Surfaces Dispersed Multiphase Flow Eulerian/Lagrangian Model Algebraic Slip Mixture Model Eulerian/Eulerian Model Eulerian/Granular Model Why model multiphase flow?! Multiphase flow is important in many industrial processes: Riser reactors Bubble column reactors Fluidized bed reactors Scrubbers, Dryers, etc. Typical objectives of a modeling analysis Maximize the contact between the different phases, typically different chemical compounds Flow dynamics Definitions Multiphase flow is simultaneous flow of: Materials with different states or phases (i.e. gas, liquid or solid). Materials with different chemical properties but in the same state or phase (i.e. liquid-liquid, such as, oil-water) The primary and secondary phases One of the phases is continuous (primary) while theother(s) (secondary) are dispersed within the continuous phase. A diameter has to be assigned for each secondary phase to calculate its interaction (drag) with the primary phase. A secondary phase with a particle size distribution is modeled by assigning a separate phase for each particle diameter Definitions (2) Dilute versus Dense phase: Refers to the volume fraction of secondary phase(s) Volume fraction of a phase = Laminar versus Turbulent Each phase could be laminar or turbulent Fluid flow (primary phase) may be turbulent with respect to the secondary phase but may be laminar with respect to the vessel In a dilute secondary phase, the small particles follow the fluid flow and typically exhibits laminar motion A dense phase at large velocities exhibits turbulent behavior Multiphase Flow Regimes Bubbly flow: Discrete gaseous bubbles in a continuous liquid Droplet flow: Discrete fluid droplets in a continuous gas Particle-laden flow: Discrete solid particles in a continuous fluid Slug flow: Large bubbles in a continuous liquid Annular flow: Continuous liquid along walls, gas in core Stratified/free-surface flow: Immiscible fluids separated by a clearly-defin