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2-D Axisymmetric Heat Source

Posted 30.04.2012, 11:09 GMT-4 Fluid & Heat, Heat Transfer & Phase Change Version 4.2a 3 Replies

George Carlin
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Hello,

I am trying to define a cylinder which contains liquid that is generating heat from fission. I am using the Non-Isothermal Flow package as I will also be simulating natural convection from temperature gradients. The model is being set up in a 2-D axisymmetric system, so I am only describing half of the cylinder with the symmetry plane cut axially through the cylinder.

I am defining this heat generation using Heat Source (Q) in Watts/m^3.

In reality, the container holds 15 litres and is generating an overall heat of 20,000 Watts. This means an average generation of 1.33*10^6 Watts/m^3.

When inputting this into a 2-D axisymmetric model, will this average heat generation value reflect the overall 20,000 watts of heat generation? I have the model running, I am just not sure if the heat generation is correct and wanted to make sure that using a 2-D model can comprehend the watts/volume heat generation term.

Thank you for any help!
3 Replies Last Post 05.05.2012, 23:16 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 30.04.2012, 14:14 GMT-4
Hi

the best is to integrate over the full volume i.e. domain (surface) integration in 2D-axi of "Q*2*pi*r" with Q=W/m^3. this should give you the full total power. If you remove the "Q" and only integrate "2*pi*r" you should get your cylinder volume.

Do not forget the"loop" length in 2D-axi. You can also turn on the implicit 2*pi*r multiplicant by changing the tick in the advanced integration tab

--
Good luck
Ivar
Hi the best is to integrate over the full volume i.e. domain (surface) integration in 2D-axi of "Q*2*pi*r" with Q=W/m^3. this should give you the full total power. If you remove the "Q" and only integrate "2*pi*r" you should get your cylinder volume. Do not forget the"loop" length in 2D-axi. You can also turn on the implicit 2*pi*r multiplicant by changing the tick in the advanced integration tab -- Good luck Ivar
George Carlin
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Posted: 1 decade ago 03.05.2012, 11:48 GMT-4
Hi Ivar,

Thank you for the suggestions. I'm trying to figure out where the advanced integration tab is located in COMSOL. Could you guide me?

Right now I'm using a value of 20,000W/15L * 1000L/m3 = 1.33*10^6 W/m3 in the General Source Option in my Heat Source property. Is this not correct?

I'm just trying to make sure the heat source value I'm entering is simulating the correct amount of heat.

Thanks for the help,
George
Hi Ivar, Thank you for the suggestions. I'm trying to figure out where the advanced integration tab is located in COMSOL. Could you guide me? Right now I'm using a value of 20,000W/15L * 1000L/m3 = 1.33*10^6 W/m3 in the General Source Option in my Heat Source property. Is this not correct? I'm just trying to make sure the heat source value I'm entering is simulating the correct amount of heat. Thanks for the help, George
Jim Freels mechanical side of nuclear engineering, multiphysics analysis, COMSOL specialist
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Posted: 1 decade ago 05.05.2012, 23:16 GMT-4
Under the derived values portion of the model tree (which is within the results portion), you can define integral values. For the axi-symmetric models, you can specify to rotate to 3D (i.e., sweep in the azimuthal direction). You can verity accuracy by first integrating the volume itself to obtain the 3D swept volume by using 1 for the integrand. Then replace 1 with the volumetric heat source to get the total power.
Under the derived values portion of the model tree (which is within the results portion), you can define integral values. For the axi-symmetric models, you can specify to rotate to 3D (i.e., sweep in the azimuthal direction). You can verity accuracy by first integrating the volume itself to obtain the 3D swept volume by using 1 for the integrand. Then replace 1 with the volumetric heat source to get the total power.

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