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How to define Vacuum Conditions in OpenFoam

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Old   August 26, 2019, 06:46
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  #41
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Raza Javed
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Quote:
Originally Posted by simrego View Post
I think you see some conduction through the air.

This is the output of



Code:
wallHeatFlux -region air -latestTime



Code:
Wall heat fluxes [W]
airTop
    convective: 0
    radiative:  5.796363e-07
    total:      5.796363e-07
airLeft
    convective: 0
    radiative:  6.173778e-07
    total:      6.173778e-07
airRight
    convective: 0
    radiative:  6.460372e-07
    total:      6.460372e-07
airBack
    convective: 0
    radiative:  -3.128043e-06
    total:      -3.128043e-06
airBottom
    convective: 0
    radiative:  6.3663e-07
    total:      6.3663e-07
air_to_heater
    convective: 3.336472e-05
    radiative:  6.121647e-07
    total:      3.397688e-05
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Old   August 26, 2019, 07:13
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Yes but your air is steady(all zero velocity), so it is a conduction not a convection (It is like your air is a solid medium). This is why I think your material props are not correct for vacuum. This "concective" flux should be really small, close to zero since there is no media to convect (or conduct) the heat.
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Old   August 26, 2019, 07:26
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Quote:
Originally Posted by simrego View Post
Yes but your air is steady(all zero velocity), so it is a conduction not a convection (It is like your air is a solid medium). This is why I think your material props are not correct for vacuum. This "concective" flux should be really small, close to zero since there is no media to convect (or conduct) the heat.

I think it is writing convection because in the region properties we declared Air as a Fluid, and normally convection occurs between solid and a fluid.

Now, we can be sure that our radiation is working?

Below are the results for the same case but without radiation:


Code:
Wall heat fluxes [W]
airTop
    convective: 0
    radiative:  -0
    total:      0
airLeft
    convective: 0
    radiative:  -0
    total:      0
airRight
    convective: 0
    radiative:  -0
    total:      0
airBack
    convective: 0
    radiative:  -0
    total:      0
airBottom
    convective: 0
    radiative:  -0
    total:      0
air_to_heater
    convective: 3.341257e-05
    radiative:  -0
    total:      3.341257e-05

End
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Old   August 26, 2019, 08:23
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It seems like it's working
I told you to run in both cases because in earlier (i think you are using a never version) versions it only wrote the sum flux (rad+conv)
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Old   August 26, 2019, 08:33
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Quote:
Originally Posted by simrego View Post
It seems like it's working
I told you to run in both cases because in earlier (i think you are using a never version) versions it only wrote the sum flux (rad+conv)

Yes I RUN both cases, and I posted here the results of both (with and without radiations).



In with radiation, it is showing radiation on every boundary.


In withour radiation, it is showing only convection only on air to heater boundary.
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Old   August 26, 2019, 08:38
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I know u did in both cases, I just told you why I gave you this advice.
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Old   August 26, 2019, 08:46
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Quote:
Originally Posted by simrego View Post
I know u did in both cases, I just told you why I gave you this advice.

Oh I see.



But I must say, you really helped a lot. I really appreciate this.


Thank you so much for your prompt replies.


I might ask you again, if I have some doubt.


Thank you once again..
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Old   September 1, 2019, 15:01
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Hello,


Sorry to disturb you again.


In my geometry, I am putting fvOptions in the heater region, the volume of my region is 0.000125m3. And the power I am putting is 1W. So I am using specific mode in fvOptions and I am putting the value 1W/0.000125m3=8000.


My fvOptions is given below:


Code:
heatSource
{
    type            scalarSemiImplicitSource;
    active          true;
    selectionMode   all;

    scalarSemiImplicitSourceCoeffs
    {
        selectionMode   all;
        volumeMode      specific;//absolute;
        injectionRateSuSp
        {
            h           (8000 0);
        }
    }
}

Now, to check what should be the temperature of my heater region, can I use boltzman law of radiation like below?


P = e*sigma*A*(T)^4
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Old   May 9, 2022, 13:38
Default thermophysical properties of vaccum
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Patrick Saft
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Hello togther,


Raza, i have a similiar problem as you. I also have to calculated vaccum.


How do you finally realised it?


which thermophysical properties have you taken?


thank you


kind regards
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