Theory and modeling of multiphase flows

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Theory and modeling of multiphase flows
Payman Jalali Department of Energy and
Environmental Technology Lappeenranta University
of Technology Lappeenranta, Finland Fall 2006
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Introduction to the CFD modeling of multiphase
flows
In the first part of this course, after some
introductory discussion on continuum mechanics
and derivation of governing equations in
single-phase fluid flows, we reviewed the
elementary modeling methods of two-phase flows,
namely homogeneous flow theory and separated
flow theory. In the second part of this course,
we will focus on the methods used in CFD
modeling.
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Introduction to the CFD modeling of multiphase
flows
Different modeling methods are used for
gas-liquid or gas-solid mixtures as shown in the
table.
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Introduction to the CFD modeling of multiphase
flows

• Some industrial fluid flow processes can be
  mentioned below
• Single-phase flows
• - Combustion chambers, furnaces - Flow in
  pipelines
• - Gas dispersion - Internal combustion engines
• - Gas fires and explosions
• Multi-phase flows
• - Flow in pipelines - Gas/liquid seperators
• - Coal combustors - Fluidized beds
• - Diesel engines - Aerated bio-reactors

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Introduction to the CFD modeling of multiphase
flows

• The need for flow simulations
• Strong influence of design parameters on the
  various processes occuring in industrial
  equipment
• Computer simulation of the interactions of the
  processes in a flowing system will improve
• - Basis for new designs
• - Estimation of operational characteristics
• - Better basis of performance of equipment from
  various vendors
• - Efficiency of various counter-measures in
  safety analysis

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Introduction to the CFD modeling of multiphase
flows
Modeling Zero- versus multi-dimensional CFD
models

• Multi-dimensional CFD models
• Set of partial differential equations
• Momentum equations need to be solved

• Zero-dimensional models
• Set of ordinary differential equations
• No momentum equations need to be solved

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Introduction to the CFD modeling of multiphase
flows

• Different classes of methods exist in the
  modeling of multiphase flows
• PSIC (Particle-Source-In-Cell)
• - Continuous phase (liquid or gas) is Eulerian
• - Dispersed phase (bubbles, droplets or
  particles) is Lagrangian
• Volume Of Fluid (VOF) technique
• - The interface between gas and liquid is
  calculated and thus it is able to resolve the
  details of the bubble shape as it moves through
  the liquid
• Multi-fluid method
• - Phases are treated as interpenetrating fluids
  that share the space and interact with
  each other through the source terms

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Introduction to the CFD modeling of multiphase
flows
Multi-fluid method Transport equations governing
the conservation of mass, momentum, and
scalar variables like turbulent quantities kl and
?l for gas-liquid flows, enthalpy (hk) and
concentration of chemical species (Yj,k) are
derived for each phase k.
Conservation of mass for phase k
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Introduction to the CFD modeling of multiphase
flows
Conservation of momentum for phase k
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Introduction to the CFD modeling of multiphase
flows
Conservation of scalars for phase k
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Introduction to the CFD modeling of multiphase
flows
Interfacial forces
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Introduction to the CFD modeling of multiphase
flows
Shape regimes for bubbles and drops
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Introduction to the CFD modeling of multiphase
flows
Drag force
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Introduction to the CFD modeling of multiphase
flows
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Reference
Hjertager B.H., Basic numerical analysis of
multiphase flows, Lecture notes, HUT, ESPOO (2006)