"Fluent case" 04: Simulating bubbling fluidized bed with Ddpm+dem

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1 Introduction
2 Problem description
3 Preparation
4 FLUENT pre-processing

1 Introduction
The DEM collision model extends the capabilities of the DPM model and can be used to simulate dense particle flows. This model can be used in conjunction with the DDPM (Dense DPM) model to simulate the blocking effect of particles on the main phase, so it can be used in bubbling fluidized beds, risers, pneumatic conveying systems, and mud flow. The DEM model is particularly useful for the following situations:

When the particle size distribution is wide
When the calculation grid is relatively rough
This case demonstrates the use of the DDPM model, where particle collisions are considered through the DEM model.

2 Problem description
In this example, we will simulate a bubbling fluidized bed and determine its behavior at a given apparent speed. The size of the rectangular bed is 0.2m, 0.2m and 0.4m. Initially, some particles are pre-loaded, and the apparent velocity is 0.5m / s. The pressure drop across the bed is detected as shown.
For the classic fluidization curve, if the apparent velocity at the inlet of the fluidized bed is small, the fluidized bed will not be sulfided and behaves like a packed bed. When the velocity increases, the fluidized bed starts to fluidize.

A classic way to understand this phenomenon is the fluidization curve. At this time, the pressure required by the inlet to drive the fluid is a function of the apparent velocity. When in a packed bed condition, the pressure is directly proportional to the increase in apparent velocity. However, when the initial fluidization conditions are reached, the pressure always remains at a constant value (time average). The stable pressure in the fluidized condition is sufficient to maintain the buoyancy of the fluidized bed. in other words:
<P> inlet × Ainlet = Buoyant weight of bed
<P> inlet × Ainlet = Buoyant weight of bed

In this example, we will simulate the fluidization process of a fluidized bed at a given apparent velocity.

3 Preparation
File preparation: copy bed.msh, 92Kparcels.inj and view-0.vw files to the working directory
Open FLUENT in 3D and Double Precision
4 FLUENT pre-processing
Step 1: Mesh

Use the menu File | Read | Mesh ... to read the mesh file bed.msh
Step 2: General

Click the Check button in the right panel to check the imported mesh to ensure that there is no negative volume
Activate the Transient option to use transient calculations
Step 3: Models

Set up the DDPM model and set it up as shown
Step 4: DPM model settings

Mouse click on the model tree node Models and double click on Discrete Phase in the models list on the right
A dialog box will pop up as shown in the figure.
Switch to the Physical Models tab and activate the DEM Collision option as shown.
Click the Injections ... button below the Discrete Phase Model dialog

Click the Create button to bring up the set Injection Properties dialog box.
Select Injection Type as file
Select Discrete Phase Domain as Phase-2
Select DEM Collision Partner as dem-anthracite
Set Stop Time to 1e-8
Click the File… button and select the file 92Kparcels.inj in the file selection dialog that opens
Switch to the Physical Models tab and set Drag Law to Wen-Yu
Click the OK button to close the dialog

Return to the Discrete Phase Model dialog.

Click the DEM Collisions… button below the Discrete Phase Model dialog box, and a dialog box will pop up as shown

Select dem-anthracite and click the set ... button.
Select the dem-anthracite-dem-aluminum in the Collision Pairs list and set it as shown
Select dem-athracite-dem-anthracite in the list item and set as shown.

Click the OK button to exit the dialog.
Step 5: Set operating pressure
Click the model tree node Cell Zone Conditions and click the button Operating Conditions .. in the right panel, as shown.
Step 6: Setting the boundary conditions
Select the model tree node Boundary Conditions.

In the parameter panel on the right, use the mouse to select the option in the Zone list box, make sure that the Phase drop-down box selection is mixture, click the Edit… button to pop up the parameter setting dialog box, switch to the DPM tab page, and set as shown.

Close the OK button to close the dialog box and return to the boundary condition setting panel.
Still select inlet, set the Phase drop-down box to phase-1, and click the Edit… button to pop up the parameter setting dialog box. Set Velocity Magnitude to 0.5. Click the OK button to close the dialog.
To set the outlet boundary, use a similar method, set the Mixture type, and set as shown.
Step 7: Solution Controls
Set the sub-relaxation factor:
I. Pressure: 0.9
II. Momentum: 0.2
III. Volume Fraction: 1
IV. Discrete Phase Sources: 1

Step 8: Monitors

Click the model tree node Monitors, click the Create button under Surface Monitors in the right panel, press to set in the pop-up dialog box, and click the OK button to close the dialog box.
Step 9: Solution Initialization
Just initialize it.

Step 10: Run Calculation
The calculation is performed in three steps:

1. Inject particles into the computational domain using a single time step
2. Calculate two seconds
3. Calculate for two more seconds

Set Time Step Size to 0.001
Set Number of Time Steps to 1
Set Report Interval to 5
Click on Calculate


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[FLUENT case] 04: Simulation of bubbling fluidized bed using DDPM + DEM