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Practical 6

This document outlines a practical exercise for students in Unit Operations I, focusing on modeling mass transfer and species diffusion in a porous medium using COMSOL Multiphysics. It details the steps for setting up the workspace, creating geometry, assigning material properties, defining boundary conditions, meshing, running simulations, and visualizing results. Additionally, it includes instructions for conducting a parametric study on the effect of porosity on diffusion and exporting results.

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Theodore Rogers
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19 views3 pages

Practical 6

This document outlines a practical exercise for students in Unit Operations I, focusing on modeling mass transfer and species diffusion in a porous medium using COMSOL Multiphysics. It details the steps for setting up the workspace, creating geometry, assigning material properties, defining boundary conditions, meshing, running simulations, and visualizing results. Additionally, it includes instructions for conducting a parametric study on the effect of porosity on diffusion and exporting results.

Uploaded by

Theodore Rogers
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Course: Unit Operations I (Transport Phenomena)

Practical 6: Diffusion of a Species in a Porous Medium

Objective

This exercise introduces students to mass transfer modeling in COMSOL Multiphysics, focusing on
species diffusion in a porous medium.

Step 1: Setting Up Your COMSOL Workspace

1. Open COMSOL Multiphysics.

2. In the Model Wizard:

o Select 2D as the space dimension.

o Under Physics, choose Transport of Diluted Species (tds).

o Click Study and select Time-Dependent.

o Click Done to create your workspace.

Step 2: Creating the Geometry

1. Navigate to the Geometry node.

2. Create a rectangular domain to represent a porous medium:

o Go to Geometry > Rectangle.

o Set Width = 1 cm and Height = 5 cm.


o Click Build All to generate the shape.

Step 3: Assigning Material Properties

1. Navigate to the Materials node.

2. Add a Custom Material and set the following properties for the porous medium:

o Diffusion Coefficient (D): 1e-9 [m²/s] (for slow diffusion in a porous solid).

o Porosity (ε): 0.35

Step 4: Defining Boundary Conditions

1. Navigate to the Transport of Diluted Species (tds) node.

2. Apply a Constant Concentration at the Left Boundary (Diffusing Species Source):

o Select the left edge of the rectangle.

o Set Concentration = 1.5 mol/m³.

3. Apply a No Flux Condition on the remaining edges

o Select the remaining edges of the rectangle.

o Choose No Flux Condition (-n·N = 0).

Step 5: Setting Up the Mesh

1. Navigate to the Mesh node.

2. Choose Physics-Controlled Mesh and select Finer.

3. Click Build All to generate the mesh.

Step 6: Running the Simulation

1. Navigate to the Study node.

2. Under Time Settings, set:

o Initial Time: 0 s

o Final Time: 1000 s

o Time Steps: 50 s

3. Click Compute to run the simulation.


Step 7: Visualizing Results

7.1 Concentration Distribution (Surface Plot)

7.2 Concentration Profile Along the Length of the Medium

Step 8: Parametric Study - Effect of Porosity on Diffusion

1. Navigate to the Study node.

2. Add a Parametric Sweep under Study Extensions.

3. Select Porosity (ε) as the parameter to vary.

4. Define values for different porosities: 0.25, 0.35, 0.50.

5. Click Compute to observe how porosity affects species transport.

Step 9: Determine the Concentration at a Specific Point

1. Find the concentration at the midpoint after 1000 s

Step 10: Exporting Results

1. Save your work as a COMSOL file.

2. Export concentration distribution as an image:

o Go to Results > Export and select Image.

o Save the image with your preferred resolution.

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