CFD Online Discussion Forums - sprayFoam Evaporation Model

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sprayFoam Evaporation Model

HI
I am a new foamer and now i meet a problem that i can not solve, please help me if u know.:)

i use sprayFoam in OF 2.3.0 to simulate SPRAY A (900K atmosphere), PhaseChangeModel, LiquidEvaporationBoil (default setting). The liquid should evaporate quickly because atmosphere T is 900K. However, the evaporation rate is very slow.

My friend told me that, 2.3.0 sprayFoam is same as 2.0.0 dieselFoam, so i simulated it again using dieselFoam, 2.0.0, evaporationModel, standardEvaporationModel (default setting), the results seem good, evaporate and mix fast.

So, i am confused that, why there is no dieselFoam in 2.3.0 and the sprayFoam can replace the dieselFoam? is there any difference in Ecaporation Model? or it just changes another name?

Thanks u:):):):)

Quote:

Originally Posted by lx882211 (Post 569252)

can anybody help me?

Hi,
do you solve your problems?
I am having similar problems with sprayFoam since I see that, considering even the aachenBomb tutorial, the spray starts to evaporate even if both gas and liquid temperature are imposed at 300K. On my opinion this is not true.
Opinions regarding this point are welcome!
Stefano

Quote:

Originally Posted by Stefano Puggelli (Post 579915)

sorry i haven't solve it, which version you use OF?

The version that I am using is the 2.3.1

Quote:

Originally Posted by Stefano Puggelli (Post 579917)

The version that I am using is the 2.3.1

in 2.3, PhaseChangeModel includs the evaporationModel in 2.0, it depends on the parameters, but i am not sure how to set it.

Hi,

some time ago I had similar problems with the evaporation rate in sprayFoam.

Quote:

Originally Posted by Stefano Puggelli (Post 579915)

the spray starts to evaporate even if both gas and liquid temperature are imposed at 300K.

As long as you don't have saturated vapor in your fluid domain there will always be a mass transfer from spray to carrier phase due to evaporation (not boiling).

Have a look at the source code of the liquidEvaporationBoil model:

Code:

else

            {

                // evaporation



                // surface molar fraction - Raoult's Law

                const scalar Xs = X[lid]*pSat/pc;



                // molar ratio

                const scalar Xr = (Xs - Xc)/max(SMALL, 1.0 - Xs);



                if (Xr > 0)

                {

                    // mass transfer [kg]

                    dMassPC[lid] += pi*d*Sh*Dab*rhos*log(1.0 + Xr)*dt;

                }

            }

This is for evaporation only, so T < TBoil and no saturated vapor.
As you can see the mass transfer is strongly dependent on the 'molar ratio' (which you might not change) and 'Dab' which basically is the vapor diffusivity and therefore a liquid property.
I changed this value so that the evaporation rate fits my desired values, as I needed a completely new liquid property anyway. You can find this value in the liquidProperties source code of your specific liquid (i.e. C2H6.C). Just change the value of 'D_' there and remember to look up which polynomial interpolation is used for the specific liquid (NSRDS functions).
After the changes recompile the code and it should work :)

I don't know if there are any other possibilities to 'tune' the evaporation rate, but this worked perfectly for me.

Hi Pascal,
thank you for your quick answer.
After looking to the source code, I arrive to your considerations.
So I perfectly agree with you.
Thanks,
Stefano

Evaporation in SprayFoam

Hi I am MJavad
I have a question .
I m solving a Water spray Injection in a Air crossflow . every thing is ok but the rate of mass transfer phase change for evaporation is not noticable . I have applied LiquidEvaporation as Evaporation Model in sprayCloud and As I told after running code I can see many parcles which should be evaporated but they are in domain yet ..

Thanks If you could help me

MJavad