CFX Combustion and Radiation Training

Combustion:
Defined as an Exothermic Chemical Reaction of a fuel (For example CH
4) with an oxidant (For example O2) to form products.
Modes of Combustion:
Flame Mode: Thin Zone of intense chemical reaction called ‘flame’ exists.
Non-Flame Mode: Volumetric Combustion Process.

Applications for Combustion Modeling
Wide range of reacting flows:
Furnaces
Boilers
Process heaters
Gas turbines
Rocket engines
Predictions of:
Flow field and mixing characteristics
Temperature field
Species concentrations
Particulates and pollutants

Eddy Dissipation and Finite Rate Chemistry Combustion Model
1. We will discuss the theory of Eddy Dissipation (EDM) and the Finite Rate Chemistry (FRC) Models
2. Outline how to setup gaseous combustion processes in CFX.

PDF Flamelet: NonPremixed Combustion
1. We will discuss the PDF Flamelet (PFM) Combustion model in ANSYS CFX. This combustion model is used to analyze non
premixed gaseous combustion processes.
2. We will discuss the theory of the interaction between the PFM combustion model and turbulence in the flow field.
3. We will discuss a tool called “CFX-RIF” which is used to generate input files (Libraries) for the PFM combustion model.
4. We will outline the steps for setting up a PFM combustion case in CFX-Pre.

Partially Premixed Combustion
We will discuss Premixed and Partially premixed Combustion models in CFX
We will also discuss the use of PDF flamelet model to analyze a partially premixed combustion process.
We will study the setup of a partially premixed combustion case in CFX-Pre.

Pollutants Modelling,NOx and Soot
1. We will discuss the mechanism of NOx formation and outline the 4 different NOx models that can be activated in CFX
2. We will discuss the different soot models and outline how soot is modeled in CFX

Radiation Modeling
1. We will discuss the objective of and applications for radiation modeling
2. We will define radiation and outline the development of some mathematical models for radiation
3. We will review 2 solution methods for radiation: Spectral and Spatial
4. We will discuss the radiation models that are available in CFX and how to select the best model for a given case

Advanced Combustion Models and Related Features
Extended Coherent Flame Combustion Model
Shares the framework for the partially premixed combustion with the Burning Velocity Model
Transport Equations are solved for Mean Mixture Fraction, Mixture Fraction Variance and Reaction Progress
Idea of Flame Surface Density (FSD,
S) is introduced in this model to describe the intensity and location of the flame. ‘FSD’ is defined as the surface area of the turbulent flame per unit volume. A transport equation is used to solve for FSD

Particle Transport Modeling for Liquid Spray and Coal Combustion
General description
Particle transport equations
Particle integration algorithm
Heat and mass transfer
Transient particle tracking
Particle injection
Particle diameter distributions
Post-Processing

Method for modelling particle laden flows
A representative sample of particles is tracked through the continuous fluid
Ordinary differential equations (ODE) are integrated for position and velocity of each particle
The overall mass flow rate of the particle phase is shared amongst the representative particles, so each particle has its own mass
flow rate, and its own number rate

Simplifying Assumptions
Moving particle is treated as a moving mass point
• Abstraction from particle shape and volume
Details of the flow around the particle are neglected, e.g.
• Near particle flow field
• Vortex shedding
• Flow separation
• Boundary layers
Local properties of the dispersed phase are predicted from
spatial averaging over particle trajectories which are crossing a certain (control) volume
Not possible to predict the tracks of all physical particles
• This would require a particle flow DNS
• Using concept of representative particle trajectories

Liquid Spray Combustion
Liquid evaporation model
Multi-component evaporation
Oil combustion modelling
Droplet break-up models

Mass Transfer – Liquid Evaporation Model
Synonym: “Spray drier model”
Main difference to simple mass transfer model:
Particle can boil

Coal Combustion & Pollutant Modeling

Coal characterisation
Furnace types
Burner types
Coal pyrolysis modeling
Char oxidation modeling
NOx formation
Examples
Customization of multiphase reactions

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