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Old   October 17, 2017, 06:03
Default droplet&wall interaction, evaporation
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hi foamers,

I am currently using sprayfoam to model water injection. In terms of interaction between droplets and wall. there are currently three regimes, i.e. rebound, stick, and escape. What I need is 100% evaporation when droplets hit the wall.


Anyone could give any idea, suggestions on how to modified the lagrangian/intermediate library to achieve that? Would be really appreciated.

Best Wishes,
Li
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Old   October 26, 2017, 05:27
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I have been working on modifying the Reactingparcel (lagrangian/intermediate/parcels/Templates/ReactingParcel/ReactingParcel.C), since it is the class dealing with phase change. I have tried to add a "if" condition i.e. if td.keepParticle = false, then droplets will 100% evaporate. The new library was compiled successful. However, the simulation result shows that droplets disappeared, but no phase change occurred.

Does anyone have any idea about this? Thank you.
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Old   October 31, 2017, 05:19
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hi,

In the ReactingParcel.C file, I found particles are removed when mass falls below a threshold.

// Remove the particle when mass falls below minimum threshold
if (np0*mass1 < td.cloud().constProps().minParticleMass())
{
td.keepParticle = false;

if (td.cloud().solution().coupled())
{
scalar dm = np0*mass1;

// Absorb parcel into carrier phase
forAll(Y_, i)
{
scalar dmi = dm*Y_[i];
label gid = composition.localToGlobalCarrierId(0, i);
scalar hs = composition.carrier().Hs(gid, pc_, T0);

td.cloud().rhoTrans(gid)[cellI] += dmi;
td.cloud().hsTrans()[cellI] += dmi*hs;
}
td.cloud().UTrans()[cellI] += dm*U0;

td.cloud().phaseChange().addToPhaseChangeMass(dm);
}

return;
}

I have tried to use similar way to remove particles when particles hit the wall. I added the code below and compiled, however, particles are not removed. Wonder if anyone has any clue on this. Thanks.

if ( isA<wallPolyPatch>(pp))
{
td.keepParticle = false;

if (td.cloud().solution().coupled())
{
scalar dm = np0*mass1;

// Absorb parcel into carrier phase
forAll(Y_, i)
{
scalar dmi = dm*Y_[i];
label gid = composition.localToGlobalCarrierId(0, i);
scalar hs = composition.carrier().Hs(gid, pc_, T0);

td.cloud().rhoTrans(gid)[cellI] += dmi;
td.cloud().hsTrans()[cellI] += dmi*hs;
}
td.cloud().UTrans()[cellI] += dm*U0;

td.cloud().phaseChange().addToPhaseChangeMass(dm);
}

return;
}
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Old   November 17, 2017, 08:20
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Any suggestions??? Thanks.
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Old   November 21, 2017, 11:00
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Joseph Urich
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Hello,

If you look in StandardWallInteration.C, the stick condition sets
keepParticle = true and U = Zero.

So you could use that as the test,
if( td.keepParticle == true && U0 == Zero)

Seems unlikely that the momentum equations would ever result in velocity of precisely zero.
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Old   November 23, 2017, 08:58
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Quote:
Originally Posted by jurich View Post
Hello,

If you look in StandardWallInteration.C, the stick condition sets
keepParticle = true and U = Zero.

So you could use that as the test,
if( td.keepParticle == true && U0 == Zero)

Seems unlikely that the momentum equations would ever result in velocity of precisely zero.
Thanks a lot, Joseph, for kind help. Just to clarify that my understanding is correct. You suggested me testthe code in the ReactingParcel.C, like below, right?

if ( td.keepParticle == true && U0 == Zero)
{
td.keepParticle = false;

if (td.cloud().solution().coupled())
{
scalar dm = np0*mass1;

// Absorb parcel into carrier phase
forAll(Y_, i)
{
scalar dmi = dm*Y_[i];
label gid = composition.localToGlobalCarrierId(0, i);
scalar hs = composition.carrier().Hs(gid, pc_, T0);

td.cloud().rhoTrans(gid)[cellI] += dmi;
td.cloud().hsTrans()[cellI] += dmi*hs;
}
td.cloud().UTrans()[cellI] += dm*U0;

td.cloud().phaseChange().addToPhaseChangeMass(dm);
}

return;
}
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Old   November 28, 2017, 04:55
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i have tried to add the code below in the ReactingParcel.C, and set "stick" as particle wall interaction.

if ( mag(U0) < SMALL)
{
td.keepParticle = false;

if (td.cloud().solution().coupled())
{
scalar dm = np0*mass1;

// Absorb parcel into carrier phase
forAll(Y_, i)
{
scalar dmi = dm*Y_[i];
label gid = composition.localToGlobalCarrierId(0, i);
scalar hs = composition.carrier().Hs(gid, pc_, T0);

td.cloud().rhoTrans(gid)[cellI] += dmi;
td.cloud().hsTrans()[cellI] += dmi*hs;
}
td.cloud().UTrans()[cellI] += dm*U0;

td.cloud().phaseChange().addToPhaseChangeMass(dm);
}

return;
}

However, parcels stick on the wall rather than removed (in Paraview), and there is no big increase in the mass transfer phase change.
But I've noticed something interesting: i set the writeInterval as 0.01, the number of stick parcels on the wall is cleared as zero at the start of next writerInterval. for example,

the number of stick parcels at t = 0.059s is 30, but at t=0.06s, the the number of stick parcels is zero. I am not quite sure why this happened. anyone has any idea?

Thank you.
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Old   May 29, 2018, 14:21
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Daniel Norton
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Hi Liliu,

I'm starting to look for a very similar functionality with a droplet evaporating once it hits a wall. Did you manage to resolve this?

Thanks!
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Old   June 18, 2018, 14:57
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Hi,
Can anyone tell me where the definition for rhoTrans() is? Or can someone explain what the below line means?

td.cloud().rhoTrans(gid)[cellI] += dmi;

Best,
Scram_1
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