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WORKSHOP - IMMERSOL Radiative Heat exchange in an Electronic Box

This workshop calculates the heat exchange in an electronic box which has three printed circuit boards (PCBs) within the domain. They each radiate 50 W to the surroundings. The walls of the box are made of heat-conducting material.

The flow domain is shown below:-

 

Accessing PHOENICS-VR

From the system level:

To enter the PHOENICS-VR environment, click on the PHOENICS icon on the desktop, or click on Start, programs, PHOENICS, PHOENICS.

From the commander level:

To enter the PHOENICS-VR environment, click on the 'Run vre' icon in the left column.

In PHOENICS-VR environment,

Start with an ‘empty’ case - click on 'File' then on 'Start New Case', then on 'Core', then click on 'OK'; to confirm the resetting.

To enter VR Editor:

This is the default mode of operation .

 

Within VR Editor.

Set the domain size, activate solution of variables and set physical properties

Click on ‘Main menu’

Click on ‘Geometry’

Change the domain size under x-direction to 0.5 m

Change Switch the grid from 'Auto' to 'Manual' in X and Z, then set the 'Number of cells' in the x- and z-directions to 30

Click on 'OK' to close the Grid mesh settings dialog

 

Click on Energy Equation dialogue box, select Temperature and click on OK

 

Click on Radiation models dialogue box and select IMMERSOL. Click on OK

Click on IMMERSOL settings and:-

Enter 1.0 for the Absorption coefficient

Enter 0.0 for the Scattering coefficient

Switch the ‘Store of radiative energy fluxes’ to ON

Click on ‘Previous panel’

 

Click on ‘Properties’.

Click on Domain material box/Gases/OK/2 Air using Ideal Gas Law, STP/OK.

 

Click on Top menu/OK

 

Click 'Reset' on the Movement control panel, then 'Fit to window' to re-scale the view to fit the geometry.

 

Create INLET object

Click on ‘New Object’. Change Name to Inlet

Change the following to:

XPos: 0.0 XSize: 0.2

YPos: 0.0 YSize: 1.0

ZPos: 0.0 ZSize: 0.0

Click on Type dialogue box and select INLET. Click on OK

Click on Attributes and enter 20 C for the Temperature, 0.5 m/s for the z- direction velocity. Click on OK/OK.

 

Create OUTLET object

Click on ‘New Object’. Change Name to Outlet

Change the following to:

XPos: 0.3 XSize: 0.2

YPos: 0.0 YSize: 1.0

ZPos: 1.0 ZSize: 0.0

Click on Type dialogue box/OUTLET/OK.

Click on Attributes and change Temperature from 'In-cell' to 'User-set', and set Text to 20 C.

Click on OK/OK.

 

Create left wall, WWALL

Click on ‘New Object’. Change Name to Wwall

Change the following to:

XPos: 0.0 XSize: 0.002

YPos: 0.0 YSize: 1.0

ZPos: 0.0 ZSize: 1.0

Click on Attributes. Click on the Types dialogue box/Solids/OK

Choose ‘111 STEEL at 27 deg C’/OK

Set emissivity to 0.9.

Click on OK/OK.

 

Create right wall, EWALL, by duplication from WWALL

Click on Duplicate object button.

Use X Position button to move copied object to the right hand edge of the domain.

Click on the copied object.

Change Name to Ewall

 

Create the top wall, HWALL

Click on ‘New Object’. Change Name to Hwall.

Change the following to:

XPos: 0.0 XSize: 0.3

YPos: 0.0 YSize: 1.0

ZPos: 0.998 ZSize: 0.002

Click on Attributes.

Click on the Types dialogue box/Solids/OK

Choose ‘111 STEEL at 27 deg C’/OK

Set the emissivity to 0.9

Click on OK/OK.

 

Create the lower wall, LWALL, by duplication from HWALL

Click on Duplicate object button and click on the object which appears at the origin (object B6). Change Name to Swall.

Change the following to:

XPos: 0.2

ZPos: 0.0

Click on OK.

 

Create bottom pcb, PCB3

Click on ‘New Object’

Change Name to PCB3 (which stands for Printed Circuit Board 3).

Change the following to:

XPos: 0.2 XSize: 0.1

YPos: 0.0 YSize: 1.0

ZPos: 0.15 ZSize: 0.1

Click on Type dialogue box and select PCB. Click on OK

Click on Attributes, then Adiabatic, select Fixed heat Flux, and click OK. Set the heat source to 50.0 W.

Set the emissivity to 0.8.

Click on OK/OK.

 

Create the remaining PCB objects by Arraying the first

Click on the Array button

Change the following to:

  Dimension Pitch
X 1 0.0
Y 1 0.0
Z 3 0.3

Click on OK.

Click on Top Object twice and change Name to PCB1.

Click on OK.

Click on Middle Object twice and change Name to PCB2.

Click on OK.

 

Set remaining solution control parameters

Click on ‘Main menu’.

Click on ‘Initialisation’.

Change FIINIT Value under TEM1 to 20. (Click on > arrow to get there).

 

Click on ‘Numerics’

Change ‘Total number of iterations to 400.

 

Click on ‘Output’. Change monitor point to:

IXMON=16 IYMON=1 IZMON=16 (a point inside PCB2).

Click on Top menu/OK.

 

Running the Solver.

In the PHOENICS-VR environment, click on 'Run', 'Solver' then 'Local solver (Earth)', and click on 'OK'; to confirm running Earth.

 

Using the VR Viewer.

In the PHOENICS-VR environment, click on 'Run', 'Post processor',then GUI Post processor (VR Viewer) . Click 'OK' on the file names dialog to accept the default files.

To view:

To select the plotting variable:

To change the direction of the plotting plane, set the slice direction to X, Y or Z slice direction (927 bytes)

To change the position of the plotting plane, move the probe using the probe position buttons

probe position (927 bytes).

A typical plot from this case is:

 

Saving the results.

In the PHOENICS-VR environment, click on 'Save as a case', make a new folder called 'IMMERSOL' (e.g.) and save as 'CASE1' (e.g.).

Further studies

Do the external walls heat up?

What happens if the absorption coefficient of the fluid is changed to 0.0?

To do this, click on Menu, Models, then Settings next to Immersol.

You will also have to increase relaxation on the temperature equation to obtain convergence. Click on Numerics, and increase the total number of iterations to 500. Click on Relaxation control, then click the > arrow until T3 and TEM1 are visible. Set the DTFALS for T3 and TEM1 to -0.25 (i.e.linear relaxation), and set the MAXINC to 10 (the maximum change from iteration to iteration). 

Run Earth, and inspect the results with the Viewer. Save the results as CASE2 in the IMMERSOL folder.