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Verification of this phase change modeling

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Old   December 15, 2011, 02:20
Default Verification of this phase change modeling
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kawamura
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Hi everyone.

I'm trying to two phase flow with phase change using VOF method.
There are some approach for mass transfer modeling.
I'm interested in the following way.
mDot = K/L * grad(T)・grad(F)
Note that K refers to the mixture thermal conductivity, F refers to the volume fraction and L is the latent heat.

But I couldn't find that verification.
If you understand this correctry, please let me know the verification!
Thanks a lot.
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Old   December 20, 2011, 02:54
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Masashi Ohbuchi
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Hi, Kawamura-san,

I can not make a verification for this notation.
But I think grad(F) should be grad(F)/mag(grad(F)).
This means unit normal vector of interface.
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Old   December 20, 2011, 04:46
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kawamura
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Hi Ohbuchi-san,

thanks for your response.
but FLUENT and some people show this expression in their paper .
there is non-existence of normal vector.

I think the most accurate expression is...
mDot = 1/L *(qg-ql)・n *Aint/V (kg/m^3 /s) in evaporating
where qg and ql is heat flux in gas and liquid phase respectively,Aint is interface area,V is volume of cell and n is unit normal vector.

but getting the correct interface area is so difficult in VOF.
so I think that grad(F) may works as n・Aint/V .
but i don't get a correct understanding about this
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Old   December 21, 2011, 00:59
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Masashi Ohbuchi
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Hi. Kawamura-san,
The value of grad(F) will be very large on sharp interface, so I think some limiter function will be needed to restrict the value within 0-1.
And, I think it's impossible to determine interface area from grad(F) without assuming specific flow regime(such as stratified flow or bubbly flow).


BTW, the expression of mas transfer by heat transfer;
mDot = (k/L) grad(T) grad(F)/mag(grad(F)),
was originally introduced in following paper.

Son,G. and Dhir,V.K. A level set method for analysis of film boiling on an immersed solid surface. Nummer. Heat Transfer B,vol.52,pp.153-177.(2007)

This expression is only valid on stratified flow regime.
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Old   December 21, 2011, 01:14
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Hi Ohbuchi-san,

It's useful information for me!
Now it's starting to make sense.

I consider about assuming specific flow.

Thank you for your kindness.

Kawamura
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