LabTP Momentum

8/10/2019 LabTP Momentum

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COMSOL TUTORIAL 1: MOMENTUM TRANSFER

Consider two immiscible and viscous liquids A and B flowing at 27°C in the z-direction in a

horizontal thin slit of length 0.5 m and width 0.1 m under the influence of a pressure gradient.

Both liquids can be considered as incompressible. The inlet velocities are 25 cm/s and 45

cm/s for A and B, respectively. Determine the corresponding velocity profile for eachfluid.

To simplify the analysis it is convenient to define two subdomains or regions. The first

subdomain comprises the liquid A phase and the second one the liquid B phase. Navier-

Stokes equation seems to be suitable to perform the simulation and therefore this equation

needs to be defined as an application mode within each subdomain. Boundary conditions are

supposed to be the same on the interface. The geometry of the system may be defined as

follows.



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>> Open the COMSOL software

MODEL WIZARD

1) In the Space Dimension, we choose the 2D coordinate system given the geometry system.

Click the next button

2) In the Add Physics, we choose Fluid Flow> Single-Phase Flow> Laminar Flow (spf).

Click the plus button. Then, click next button



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3) In the Select Study Type, we click on stationary study, then click the finish button

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GEOMETRY

1) In Model Builder, right click on geometry tab and choose the rectangle.

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2) Let us draw two rectangles draw one by one, specify the dimension of the geometry, then

click on build selected.

3) Repeat step 1 and 2 to draw another rectangle.

Therefore, the geometry of the model is defined by the following figure.

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2

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1

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MATERIAL

1) In Model Builder, right click and choose material

2) In Settings> Material> Geometry Scope> Selection, we click on Domain 2(domain on

the top) and click minus button to deactive the domain

3) Scroll down the setting tab to the material content, we specify the density and dynamic

viscosity of Material 1 as below

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4) Repeat step 1 to create another material

5) Click on Domain 2(domain on the top) and click plus button to select the domain.

6) Specify the density and dynamic viscosity of Material 2 as below

PHYSICS

1) Under Model Builder> Untitle.mph> Model> Laminar Flow tab, we click laminar flowtab and change the compressibility to Incompressible flow.

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1

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2) Then, right click on laminar flow tab and click inlet to make the Inlet 1.

3) Under Settings> Inlet> Boundary Condition, we type the velocity and click on

boundary 1 for Inlet 1 as below

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MESH

1) Find Mesh 1> size then click. Select fine mesh for element size

2) Right click on Mesh 1 tab and click Free Triangular. Then, we click build selected button

Therefore, the mesh of the model is defined by the following figure.

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COMPUTE

Contour

1) Right click on the Study 1 and choose compute

Thus, the contour of the model is defined by the following figure.



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Arrow Contour

1) Under Model Builder> Untitle.mph> Results tab, right click on 2D Plot Group 1 and

select Arrow Surface

2) Under Settings> Coloring and Style, we fill the scale factor and color the color as below

and click plot button

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Therefore, the arrow contour of velocity magnitude is define by following figure



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DATA PLOT

Line Graph

1) To make cross-section line in the middle of model(x=0.25) for analysis, right click on the

Results>Data Sets tab and choose Cut Line 2D. Then, specify the x-axis and y-axis

coordinate as below.

2) To make a line plot, right click on Results and choose 1D Plot Group. Then, right click

on Results>1D Plot Group and choose Line Graph

3) Find the Data set and choose Cut Line 2D 1

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1 2



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4) Under Setting> Line Graph> X-Axis Data. Then, find and click replace expression

button, select Geometry and Mesh> Coordinate> Y-Coordinate(y)

5) On setting tab, click on plot button.

Finally, the velocity profile will be displayed as shown below

6) Save your project

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DATA CAPTURE

Contour capture

1) To capture the contour click on the Results>2D plot Group 1 tab. Then, click Image

Snapshot

2) Select and thick Include to activate title, legend, axes, and logotype. And, change the Font

size to 12 pt. Click Browse button and change to JPEG-file, specify the name, and save

anywhere to put the file.

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Data plot capture

1) To capture the data plot click on the Results>1D plot Group 2 tab. Then, fill the title, x-

axis label, and y-axis label. Then, follow same instruction on contour capture for number 1

and 2.



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LabTP Momentum