Tut 18 Euler Granular

Tutorial: Modeling Heterogeneous Reactions with

Eulerian-Granular Flow

Introduction

This tutorial demonstrates how to do the following:

• Use k-epsilon turbulence model and species transport model.

• Use user-defined function (UDF) to specify a model which is not available with ANSYSFLUENT.

• Set up the reaction of coal particles using the eulerian-granular multiphase flow.

• Solve the case using appropriate solver settings and solution monitors.

• Postprocess the resulting data.

Prerequisites

This tutorial is written with the assumption that you have completed

Tutorial 1 from ANSYS FLUENT 13.0 Tutorial Guide, and that you are familiar with theANSYS FLUENT navigation pane and menu structure. Some steps in the setup and solutionprocedure will not be shown explicitly. For more information on species transport modeland standard k-epsilon viscous model, see Sections 16, Modeling Species Transport and Finite-Rate Chemistry and 13.5.1, Setting Up the Standard or Realizable k-ε Model in the ANSYSFLUENT 13.0 User’s Guide.

Problem Description

In this tutorial, a two dimensional riser geometry is considered to simulate the combustionof coal particles using eulerian-granular multiphase flow. The gas and coal particles simulta-neously enter the domain from the same inlet. In this case, both the phases are modeled asmixture. The dry coal particles contain 2% char and 2% volatiles. The primary phase is agaseous mixture consisting of O2, N2, CO, CO2, tar, and H2O, while the secondary phase isa coal mixture of C(s), volatiles, H2O(l), and ash-coal. In this example, two heterogeneousreactions are considered, one for devolatilization and the other for char combustion. Ahomogeneous reaction of carbon monoxide converting to carbon-di-oxide is also considered.To demonstrate the case setup for eulerian-granular flow with the heterogeneous andhomogeneous reactions, consider the coal composition and the geometry.

c© Fluent Inc. October 28, 2010 1

Modeling Heterogeneous Reactions with Eulerian-Granular Flow

For the realistic coal combustion or gasification process, you need to consider more hetero-geneous and homogeneous reactions.

Setup and Solution

Preparation

1. Copy the mesh file (euler.msh.gz) and the UDF source file (mass xfer rate.c) tothe working folder.

2. Use FLUENT Launcher to start the (2D) version of ANSYS FLUENT.

For more information about FLUENT Launcher refer to Section 1.1.2, StartingANSYS FLUENT Using FLUENT Launcher in ANSYS FLUENT 13.0 User’s Guide.

3. Enable Double-Precision in the Options list.

4. Click the UDF Compiler tab and ensure that the Setup Compilation Environment forUDF is enabled.

The path to the .bat file which is required to compile the UDF will be displayed assoon as you enable Setup Compilation Environment for UDF.

If the UDF Compiler tab does not appear in the FLUENT Launcher dialog box by default,click the Show Additional Options >> button to view the additional settings.

The Display Options are enabled by default. Therefore, after you read in the mesh, itwill be displayed in the embedded graphics window.

Step 1: Mesh

1. Read the mesh file (euler.msh.gz).

File −→ Read −→Mesh...

As the mesh file is read, ANSYS FLUENT reports the progress in the console.

2 c© Fluent Inc. October 28, 2010


Step 2: General Settings

1. Define the solver settings.

General −→ Transient

(a) Select Transient in the Time list.

2. Check the mesh (see Figure 1).

General −→ Check

Figure 1: Mesh Display



Step 3: Models

Models

1. Enable the eulerian multiphase model.

Models −→ Multiphase −→ Edit...

(a) Select Eulerian from the Model list.

(b) Ensure that Number of Eulerian Phases is set to 2.

(c) Click OK to close the Multiphase Model dialog box.



2. Enable the standard k-epsilon viscous model.

Models −→ Viscous −→ Edit...

(a) Select k-epsilon (2 eqn) from the Model list.

(b) Retain the selection of Standard from the k-epsilon Model list.

(c) Select Dispersed from the Turbulence Multiphase Model list.

(d) Click OK to close the Viscous Model dialog box.



3. Enable species transport model.

Models −→ Species −→ Edit...

(a) Select Species Transport from the Model list.

(b) Enable Volumetric from the Reactions list.

(c) Disable Diffusion Energy Source from the Options list.

(d) Select Finite-Rate/Eddy-Dissipation from the Turbulence-Chemistry Interaction list.

(e) Click OK to close the Species Model dialog box.

An Information dialog box will appear informing that the material properties arechanged. Click OK.

Step 4: Materials

Materials

1. Select the materials for the solid and mixture phases.

(a) Copy materials from the database.

Materials −→ Create/Edit...

i. Click FLUENT Database... to open the FLUENT Database Materials dialogbox.

A. Select fluid from the Material Type drop-down list.

B. Copy carbon-monoxide (co), carbon-solid (c<s>), coal-hv-volatiles (hv vol),and water-liquid (h2o<l>) from the FLUENT Fluid Materials list.



C. Similarly select mixture from the Material Type drop-down list.

D. Copy coal-hv-volatiles-air from the FLUENT Mixture Materials list.

E. Close the FLUENT Database Materials dialog box.

(b) Set the properties for carbon-solid (c<s>).

i. Select fluid from the Material Type drop-down list.

ii. Select carbon-solid (c<s>) from the FLUENT Fluid Materials drop-down list.

iii. Enter 1400 kg/m3 for Density.

iv. Select constant from the Cp (Specific Heat) drop-down list and enter 2092 j/kg-k as the value.

v. Enter 0 for Standard State Enthalpy.

vi. Click Change/Create.

(c) Create a new fluid ash-coal.

i. Select carbon-solid (c<s>) from the FLUENT Fluid Materials drop-down list.

ii. Enter ash-coal as the Name and Chemical Formula.

iii. Enter 1500 kg/m3 for Density.

iv. Retain 2092 j/kg-k for Cp (Specific Heat).

v. Enter 120 kg/kgmol for Molecular Weight.

vi. Retain 0 j/kgmol for Standard State Enthalpy.

vii. Enter 210058.3 j/kgmol-k for Standard State Entropy.

viii. Click Change/Create.

A Question dialog box will appear asking change/create mixture and overwritecarbon. Click No.



(d) Set the properties for coal-hv-volatiles (hv vol).

i. Select fluid from the Material Type drop-down list.

ii. Select coal-hv-volatiles (hv vol) from the FLUENT Fluid Materials drop-downlist.

iii. Select none from the Mixture drop-down list.

iv. Enter volatile as the Name and Chemical Formula.

v. Enter 1000 kg/m3 for Density and 2092 j/kg-k for Cp (Specific Heat).

vi. Enter 56.168 kg/kgmol for Molecular Weight.

vii. Enter -1.8859e+08 j/kgmol for Standard State Enthalpy.

viii. Retain 0 j/kgmol-k for Standard State Entropy.

ix. Click Change/Create and click No in the Question dialog box that appears.



(e) Create a new material, tar.

i. Select coal-hv-volatiles (hv vol) from the FLUENT Fluid Materials drop-downlist.

ii. Select none from the Mixture drop-down list.

iii. Enter tar as the Name and Chemical Formula.

iv. Enter 1000 kg/m3 for Density and 1200 j/kg-k for Cp (Specific Heat).

v. Enter 0.1 w/m-k for Thermal Conductivity.

vi. Enter 0.001 kg/m-s for Viscosity.

vii. Enter 144 kg/kgmol for Molecular Weight.

viii. Enter 331176 J/kgmol for Standard State Enthalpy.

ix. Retain 0 j/kgmol-k for Standard State Entropy.

x. Click Change/Create and click No in the Question dialog box that appears.

(f) Create a new mixture, mixture-coal.

i. Select mixture from the Material Type drop-down list.

ii. Select mixture-template from the FLUENT Mixture Materials drop-down list.

iii. Enter mixture-coal as the Name.



iv. Click the Edit... button for Mixture Species to open the Species dialog box.

A. Add carbon-solid (c<s>), volatile, water-liquid(h2o<l>), and ash-coal.

B. Remove h2o, o2, and n2 from the Selected Species list.

Note: Ensure that the Selected Species list contains carbon-solid (c<s>),volatile, h2o<l>, and ash-coal. The last species in the Selected Specieslist is ash-coal.

C. Click OK to close the Species dialog box and click No in the dialog boxthat appears.

v. Select mixture-coal from the FLUENT Mixture Materials drop-down list.



vi. Click the Edit... button for Mechanism to open the Reaction Mechanismsdialog box.

A. Deselect reaction-1.

B. Click OK to close the Reaction Mechanisms dialog box.

vii. Select volume-weighted-mixing-law from the Density drop-down list.

viii. Ensure mixing-law is selected from the Cp (Specific Heat) drop-down list.

ix. Enter 1.5 W/m-K for Thermal Conductivity.

x. Enter 1e-12 m2/s for Mass Diffusivity.

xi. Click Change/Create.

(g) Create a new mixture, mixture-gas.

i. Select coal-hv-volatiles-air from the FLUENT Mixture Materials drop-down list.

ii. Enter mixture-gas as the Name.

iii. Click the Edit... for the Mixture Species to open the Species dialog box.

A. Remove n2 from the Selected Species list.

B. Add tar and carbon-monoxide (co) to the Selected Species list.

C. Add n2 to the Selected Species list.

This ensures that n2 appears last in the Selected Species list.

Ensure that the Selected Species list contains hv vol, o2, co2, h2o, tar,co, and n2. The last species in the Selected Species list is n2.

D. Click OK to close the Species dialog box and click Yes in the dialog boxthat appears.

iv. Select mixture-gas from the FLUENT Mixture Materials drop-down list.



v. Click Edit... for Mechanism to open the Reaction Mechanisms dialog box.

A. Ensure that reaction-1 is selected and click OK to close the ReactionMechanisms dialog box.

B. Enter 0.06 W/m-K for Thermal Conductivity.

C. Enter 6e-05 W/m-K for Viscosity.

D. Enter 1e-07 m2/s for Mass Diffusivity.

vi. Click Change/Create in the Create/Edit Materials dialog box.

2. Set the gaseous phase reaction.

(a) Select mixture-gas from the FLUENT Mixture Materials drop-down list.

(b) Click Edit... for Reaction to open the Reactions dialog box.

(c) Ensure that Number of Reactants is set to 2.

(d) Set the Number of Products to 1.

(e) Select co and o2 from the Species drop-down lists in the Reactants section.

(f) Select co2 from the Species drop-down lists in the Products section.



(g) Enter the values as shown in the following table:

Species Stoich. Coefficient Rate Exponent

co 2 1o2 1 0.25co2 2 0

(h) Enter 2.239e+12 and 1.7e+08 for Pre-Exponential Factor and Activation En-ergy J/kgmol respectively.

(i) Click OK to close the Reactions dialog box.

(j) Click Change/Create and close the Create/Edit Materials dialog box.

3. Remove hv vol from the Selected Species list for mixture-gas.

Materials −→ mixture-gas −→ Create/Edit...

Step 5: Phases

Phases

1. Select the primary phase.

Phases −→ phase-1 −→ Edit...

(a) Select mixture-gas from the Phase Material drop-down list.

(b) Click OK to close the Primary Phase dialog box.

2. Select the secondary phase.

Phases −→ phase-2 −→ Edit...



(a) Select mixture-coal from the Phase Material drop-down list.

(b) Enable Granular.

(c) Enter 0.0005 m for Diameter.

(d) Select syamlal-obrien from the Granular Viscosity drop-down list.

(e) Select lun-et-al from the Granular Bulk Viscosity drop-down list.

(f) Select schaeffer from the Frictional Viscosity drop-down list.

(g) Select syamlal-obrien from the Solids Pressure drop-down list.

(h) Select syamlal-obrien from the Radial Distribution drop-down list.

(i) Click OK to close the Secondary Phase dialog box.



Step 6: User-Defined Functions

1. Compile the UDF.

Define −→ User-Defined −→ Functions −→Compiled...

(a) Click Add... and select the source file, mass xfer rate.c.

(b) Click Build and then click Load to load the library.

2. Define function hooks.

Define −→ User-Defined −→Function Hooks...

(a) Click Edit... for Adjust to open the Adjust Functions dialog box.

i. Select gasification::libudf from the Available Adjust Functions list.



ii. Click Add and click OK to close the Adjust Functions dialog box.

(b) Click OK to close the User-Defined Function Hooks dialog box.‘

Step 7: Phase Interaction

Phases... −→ Interaction...

1. Select syamlal-obrien for the Drag Coefficient drop-down list.

2. Click the Collisions tab and enter 0.8 for Restitution Coefficient.

3. Click the Heat tab and select gunn from the Heat Transfer Coefficient drop-down list.

4. Click the Reactions tab.

(a) Set the Total Number of Heterogeneous Reactions to 2.

(b) Set Number of Reactants to 2.

(c) Retain 1 for Number of Products.

(d) Set the properties for net-reaction-1 as shown in the following table:

Phase Species Stoich. Coefficient

Reactants phase-2 c<s> 1phase-1 o2 0.5

Products phase-1 co 1

(e) Select char combustion::libudf from the Reaction Rate Function drop-down list.



5. Increase ID to 2.

(a) Retain 1 for Number of Reactants.

(b) Set Number of Products to 4.

(c) Set the properties for net-reaction-2.

Phase Species Stoich. Coefficient

Reactants phase-2 volatile 1Products phase-1 tar 0.24

phase-1 co 0.24phase-1 co2 0.24phase-1 h2o 0.231

(d) Select devolatilization::libudf from the Reaction Rate Function drop-down list.

6. Click OK to close the Phase Interaction dialog box.



Step 8: Boundary Conditions

1. Set the inlet boundary conditions.

Boundary Conditions −→ inlet gas

(a) Select phase-1 from the Phase drop-down list and click Edit... to open the VelocityInlet dialog box.

i. Ensure that Magnitude, Normal to Boundary is selected from the VelocitySpecification Method drop-down list.

ii. Enter 3 m/s for Velocity Magnitude.

iii. Select Intensity and Hydraulic Diameter from the Specification Method drop-down list in the Turbulence group box.

iv. Enter 1% for Turbulent Intensity and 0.05 m for Hydraulic Diameter.

v. Click the Thermal tab and enter 1200 K for Temperature.

vi. Click the Species tab and enter 0.75 for o2.

vii. Click OK to close the Velocity Inlet dialog box.

(b) Select phase-2 from the Phase drop-down list and click Edit... to open the VelocityInlet dialog box.

i. Enter 0.2 m/s for Velocity Magnitude.

ii. Click the Thermal tab and enter 1200 K for Temperature.

iii. Click the Species tab and enter 0.02 for carbon-solid (c<s>) and volatile.

iv. Click the Multiphase tab and enter 0.2 for Volume Fraction.

v. Click OK to close the Velocity Inlet dialog box.



2. Set the outlet boundary conditions.

Boundary Conditions −→ outlet

(a) Select phase-1 from the Phase drop-down list and click Edit... to open the PressureOutlet dialog box.

i. Select Intensity and Hydraulic Diameter from the Specification Method drop-down list in the Turbulence group box.

ii. Enter 1% for Backflow Turbulent Intensity and 0.05 m for Backflow HydraulicDiameter.

iii. Click the Thermal tab and enter 1144 K for Backflow Total Temperature.

iv. Click OK to close the Pressure Outlet dialog box.

(b) Select phase-2 from the Phase drop-down list and click Edit... to open the PressureOutlet dialog box.

i. Click the Thermal tab and enter 1144 K for Backflow Total Temperature.

ii. Click the Species tab and enter 0.02 for volatile and carbon-solid (c<s>).

iii. Click OK to close the Pressure Outlet dialog box.



Step 9: Operating Conditions

Boundary Conditions −→ Operating Conditions...

1. Enable Gravity and enter -9.81 m/s2 for Y in Gravitational Acceleration group box.

2. Click OK to close the Operating Conditions dialog box.

Step 10: Solution

1. Set the solution methods parameters.

Solution Methods

(a) Select Green-Gauss Cell Based from Gradient drop-down list.



2. Set up a volume monitor to monitor total solid volume.

Monitors (Volume Monitors)−→ Create...

(a) Enable Plot and Write for vol-mon-1.

(b) Enter vol-solid.out for the File Name.

(c) Select Flow Time from X Axis drop-down list.

(d) Select Time Step from the Get Data Every drop-down list.

(e) Select Phases... from the Field Variable drop-down lists.

(f) Select phase-2 from the Phase drop-down list.

(g) Select fluid riser from the Cell Zones group box.

(h) Click OK to close the Volume Monitor dialog box.

3. Initialize the solution.

Solution Initialization

(a) Select all-zones from Compute from drop-down list.

(b) Click Initialize.

Ensure that phase-2 Granular Temperature is not set to zero.

4. Run the calculation for 100 iterations.

Run Calculation

(a) Enter 0.001 for Time Step Size (s) and 100 for Number of Time Steps.

(b) Enable Data Sampling for Time Statistics.

(c) Enter 50 for Max Iterations/Time Step.



(d) Set Reporting Interval to 5.

(e) Click Calculate.

The 0monitor plot is used to confirm when to start the sampling. Once thequantities of interest reach a steady value, you can infer that the sampling canbe initialized.

5. Save the case and data files (euler-gran-1.cas/dat.gz).

File −→ Write −→Case & Data...

6. Calculate further for 1000 time steps by saving transient statistics.

(a) Change the Time Step Size (s) to 0.01 and enter 1000 for Number of Time Steps.

(b) Enable Data Sampling for Time Statistics.

(c) Enter 50 for Max Iterations/Time Step.

(d) Set Reporting Interval to 5.

(e) Click Calculate.

The convergence history of volume fraction on fluid riser after 1000 time steps isas shown in Figure 2.

Figure 2: Convergence History of Volume Fraction on fluid riser After 1000 Time Steps

7. Save the case and data files (euler-gran-final.cas/dat.gz).



Step 11: Postprocessing

1. Display contours of Mean Mass Fraction of co.

Graphics and Animations −→ Contours −→ Set Up...

(a) Enable Filled from the Options group box.

(b) Select Unsteady Statistics... and Mean Mass Fraction of co from the Contours ofdrop-down lists.

(c) Select phase-1 from the Phase drop-down list.

(d) Click Display (see Figure 3).

Figure 3: Contours of Mean Mass Fraction of co

2. Similarly, display contours of Mean Mass Fraction of o2.

(a) Select Unsteady Statistics... and Mean Mass Fraction of o2 from the Contours ofdrop-down list.

(b) Select phase-1 from the Phase drop-down list.

(c) Click Display (see Figure 4).

(d) Close the Contours dialog box.

3. Display contours of mean temperature of phase-2.

(a) Select Unsteady Statistics... and Mean Static Temperature from the Contours ofdrop-down lists.

(b) Select phase-2 from the Phase drop-down list.

(c) Click Display (see Figure 5).



Figure 4: Contours of Mean Mass Fraction of o2

Figure 5: Contours of Mean Static Temperature of phase-2



Summary

This tutorial demonstrates the use of heterogeneous reactions for modeling gasificationproblems. In this tutorial, only three reactions are used.

Further Improvements

While working on realistic cases, you can include more number of heterogeneous as well asvolumetric reactions. Further, heterogeneous stiff solvers can be used for the stiff reactions.Instead of using the UDF for heterogenous reaction rate you can use arrhenius-rate forReaction Rate Function.


Tut 18 Euler Granular

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Transcript of Tut 18 Euler Granular