[aminhgn]

Hi,

I am trying to model mass transfer between air and air. My equation is as follow:

m_lg = ((density of gas*Ds) / (1- mass fraction water vap t the interface))*(dc/dy)

I want to use define_mass transfer as follow:

#include "udf.h"

DEFINE_MASS_TRANSFER(liq_gas_source, cell, thread, from_index,

from_species_index, to_index, to_species_index)

{

Thread *liq = THREAD_SUB_THREAD(thread, from_index);

Thread *gas = THREAD_SUB_THREAD(thread, to_index);

real m_lg;

m_lg = (-2.88e-5*C_R(cell,gas)/(1-C_YI(cell,gas,0)))*C_YI_G(cell,gas,0)[1];

return (m_lg);

}

but every time I use gradient I get a fatal error after one iteration. In addition, I set solve/set/expert/linearized mss transfer to no and (rpsetvar 'species/save-gradients? #t) for gradient for pressure-bsed.

I hope that anyone can help me with it.

[pakk]

Originally Posted by aminhgn

Hi,

I am trying to model mass transfer between air and air. My equation is as follow:

m_lg = ((density of gas*Ds) / (1- mass fraction water vap t the interface))*(dc/dy)

I want to use define_mass transfer as follow:

#include "udf.h"

DEFINE_MASS_TRANSFER(liq_gas_source, cell, thread, from_index,

from_species_index, to_index, to_species_index)

{

Thread *liq = THREAD_SUB_THREAD(thread, from_index);

Thread *gas = THREAD_SUB_THREAD(thread, to_index);

real m_lg;

m_lg = (-2.88e-5*C_R(cell,gas)/(1-C_YI(cell,gas,0)))*C_YI_G(cell,gas,0)[1];

return (m_lg);

}

but every time I use gradient I get a fatal error after one iteration. In addition, I set solve/set/expert/linearized mss transfer to no and (rpsetvar 'species/save-gradients? #t) for gradient for pressure-bsed.

I hope that anyone can help me with it.

You tell your UDF to calculate the mass flux based on the gradient calculated in the previous iteration. That fails in the first iteration, because there is no previous iteration.


The practical solution is to run your simulation without this UDF for a few time steps, and then add it.

[aminhgn]

Originally Posted by pakk

You tell your UDF to calculate the mass flux based on the gradient calculated in the previous iteration. That fails in the first iteration, because there is no previous iteration.


The practical solution is to run your simulation without this UDF for a few time steps, and then add it.

Thank you for your reply. Yeah so I let it run for a while then i add my FUNCTION but still after one iteration suddenly diverge.

[pakk]

Then you might have cells were C_YI(cell,gas,0)=1, so your equation becomes infinite.

[Converged001]

Originally Posted by aminhgn

Thank you for your reply. Yeah so I let it run for a while then i add my FUNCTION but still after one iteration suddenly diverge.

hi,I see that many people think the unit of the return value of DEFINE_MASS_TRANSFER is Kg/cubic meter*s).But,I think in your UDF,the unit of the return value is Kg/（Square meter*s).Maybe you can have a try.

[RestlessBreeze]

Hello, I am also working on the topic of droplet evaporation based on Fick's law recently. I would like to ask if your problem is solved.