Quiz 12 Flashcards
What is a multiphase flow?
o Simultaneous flow of:
▪ Materials with different states or phases
• Gas – Liquid – Solid
o Materials with different chemical properties but in the same state or phase
▪ Liquid – Liquid (oil – water)
What are the multiphase flow regimes Phil mentions?
o Bubbly flow: discrete gaseous bubbles in a continuous liquid
o Droplet flow: discrete fluid droplets in a continuous gas
o Particle-laden flow: discrete solid particles in a continuous fluid
o Slug flow: large bubbles in a continuous liquid
o Annular flow: continuous liquid along walls, gas in core
o Stratified and free-surface flow: immiscible fluids separated by a clearly-defined interface
What is the Lagrangian approach to CFD modelling of multiphase flows?
o Fluid phase is a continuum
o Time average taken by following a certain particle and observing it at some time interval
o Particle trajectories are calculated from the equation of particle motion
o Lagrangian averages are popular especially in modeling the dynamics of a single particle or a dilute suspension
What is the Eulerian approach to CFD modelling of multiphase flows?
o Particle phase treated as a continuum
▪ Conservation equations for momentum and mass
o Constitutive equations
▪ Close the equation system by taking into account the structure of the flow field and material properties by experimental correlations
o Interfacial conditions
Which approach does FDS use?
Lagrangian
Which of the coupling stages between phases is at last needed for a practical sprinkler application?
o Two-way coupling: ▪ Mass, momentum and energy ▪ Examples include: • Inert particle heating and cooling • Droplet evaporation, boiling • Particle devolatilization, charring
Would you trust FDS enough to use the sprinkler model in a real case when using an analytical approach to design? Motivate your answer.
Maybe, depends on what aspect ▪ Activation – probably ▪ Smoke movement – maybe ▪ Smoke layer cooling – maybe ▪ Extinction – not likely
