Barracuda官方教程阅读笔记(一)

Introduction to CPFD Software and the Barracuda Virtual Reactor

Fluid-Particle flows

Examples

  • Fluidized Beds
  • Ore Reactors
  • Cyclones
  • Risers
  • Deep Beds

What is different than single phase flows?

Particles are NOT fluids:

  • Particles are discrete entities (cannot be subdivided like a fluid)
  • Particles have a size distribution
  • Particle cannot completely fill a space
  • Particles occupy a physical volume (and displace fluid)
  • Particles CAN support a shear stress (while fluids CANNOT support a shear stress)

Other considerations:

  • Coupling between particles and fluids
  • Wall treatments
  • Boundary treatment
  • Thermal, chemistry…

Modeling approaches

To accurately simulate fluid-particle flows, one must model the effects of:

  • Drag and coupling
    • Dilute flows (<1% by volume)
    • Dense flows (up to close pack)
  • Many particle sizes or size distribution
  • Multiple types of particles (size, density, composition)
  • Particle interactions (walls, other particles)
  • Heat transfer
  • Chemical reactions
    • Gas-phase (homogeneous)
    • Gas + particles (heterogeneous)
    • Changing particle composition

There are different approaches to modeling particle flows

Modeling Approachs
Single Phase
Multi-Phase
Eulerian
Lagrangian
Eulerian/Eulerian
Eulerian/Lagrangian
Unidirectional Coupling
Bi-directional Coupling: Barracuda VR

The CPFD? modeling approach

Overview

  1. What about the large number of particles?
    • Lesser number of computational particles
    • The particle field is resolved by using a reasonable number of computational particles
    • Each computational particle represents one or more actual particle(s) with identical physical properties
    • The physics are computed on the individual particle (e.g. drag based on size, chemistry, etc.)
    • All changes experienced by the computational particle are applied to all actual particles represented by that computational particle (proper fluid displacement)
    • Many CPFD calculations utilize between 500,000 and 5,000,000 computational particles
  2. What about particle contact and collision?
    • Modeled, rather than directly computed
    • Collision detection can be prohibitive with millions of computational particles
    • Rather than computing which particle a given computational particle will impact, the CPFD method is more concerned with the question “is a collision likely to occur?”
    • The collisions are then subjected to various models
      • Enduring contact at close-pack handled via a non-linear stress tensor
      • BGK-type collisional damping
  3. What about inter-phase coupling?
    • Inter-phase interpolation operators, and tight, bi-directional coupling
    • Different particles experience different motion, even though both are in the same cell
    • All sub-grid particle motion is coupled back to the fluid phase momentum equation

Advantages and disadvantages

Advantages:

  • PSD
  • Erosion
  • Number of particles

Disadvantages:

  • Direct particle contact
  • Multiple particles must fit in cell

Validation

  • U m f U_{mf} Umf
  • dP/dz
  • 2D Bed
  • PSRI Jet Cup

Commercial examples and case studies

Biomass CFB combustor

FCC regenerator

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