[Anshs]

I meant to say, the conditional statement is not working. The mass transfer is working on the full fluid phase. Rest of it is fine.

Thanks.

[Anshs]

Originally Posted by vinerm

What do you mean by not working? Is it not compiling, or giving run-time error, or giving wrong values?

Fluent does not accept // for comments. So, either use /* */ or remove comments altogether.

The condition statement for interfacial mass transfer is not working.

Thanks

[vinerm]

That won't have any effect if both the phases are rather well-mixed, otherwise, it should work. Try plotting volume fraction of phases.

[Anshs]

Originally Posted by vinerm

That won't have any effect if both the phases are rather well-mixed, otherwise, it should work. Try plotting volume fraction of phases.

I did plot the volume fraction.

The image below represents the mass transfer which I have used

Screenshot 2020-06-02 at 4.37.19 PM.jpg

Initial Volume fraction: Water
water.jpg
Oil
oil.jpg

Phase interaction: mass transfer: after 100 timesteps.

Screenshot 2020-06-02 at 3.41.03 PM.jpg

[vinerm]

How many phases do you have? Since the right-most region neither has water nor oil. So, is there a third phase?

[Anshs]

Originally Posted by vinerm

How many phases do you have? Since the right-most region neither has water nor oil. So, is there a third phase?

Yes there re 3 phases.

Screenshot 2020-06-02 at 6.05.48 PM.png

Screenshot 2020-06-02 at 6.05.54 PM.png

[vinerm]

Do you want mass transfer from gas to water or gas to oil? You have to ensure that you have selected correct phases under From and To in Mass Transfer Panel.

[Anshs]

Originally Posted by vinerm

Do you want mass transfer from gas to water or gas to oil? You have to ensure that you have selected correct phases under From and To in Mass Transfer Panel.

None, I want mass transfer (species) from water to oil. I have posted the 'phase interaction tab' in the reply as well. you may have a look.

Thanks

[vinerm]

Your post does not contain Mass Transfer Tab. Anyway, then make changes to your code and use oil in place of gas. Though that is just a variable name yet it helps to remove ambiguity. Furthermore, to debug the code, try to make the condition even stricter. Use product of C_VOF(c, t, water) & C_VOF(c, t, oil) to define m_lg. This will have a non-zero value only at the interface of water and oil.

[Anshs]

Originally Posted by vinerm

Your post does not contain Mass Transfer Tab. Anyway, then make changes to your code and use oil in place of gas. Though that is just a variable name yet it helps to remove ambiguity. Furthermore, to debug the code, try to make the condition even stricter. Use product of C_VOF(c, t, water) & C_VOF(c, t, oil) to define m_lg. This will have a non-zero value only at the interface of water and oil.

The mass transfer is working fine between water and oil phase, but it is also operating in some region between water and air (3rd phase).

Phases: Screenshot 2020-06-04 at 11.19.16 PM.jpg

Mass transfer rate: mt.jpg

UDF:

#include "udf.h"



DEFINE_MASS_TRANSFER(interface_transfer, cell, thread, from_index, from_species_index, to_index, to_species_index)

{

real m_lg;


Thread *water = THREAD_SUB_THREAD(thread, from_index);

Thread *oil = THREAD_SUB_THREAD(thread, to_index);



m_lg = 0.0;




if ( C_VOF(cell,water)*C_VOF(cell,oil) != 0 )

{

/*m_lg = 0.1*C_VOF(cell,gas)*C_R(cell,gas)*

fabs(t_sat -C_T(cell,gas))/t_sat;

m_lg = 0.1* C_VOF(cell,gas) * C_R(cell,gas) * C_YI(cell , gas , 0) ; */

m_lg = 100;

/* here C_YI(c, gas, 0 ), denotes species mass fraction of 1st species in the mixture denoted by phase 'gas'.*/

}


else m_lg = 0.0;
return (m_lg);

[vinerm]

That's because there are three phases. I suggested product of volume fractions assuming there are two phases. But with three phases, even with 0.1 volume fractions of water and oil, the condition matches, despite there being 80% air. So, you have to use a condition wherein the air content is extremely low. Ideally, this would mean that the product of volume fractions of oil and water should be 0.25. But that's ideal case, not practical. So, a better approach would be to ensure that the sum of water and oil volume fraction is close to 1, say, above 0.95, as well as their product is close to 0.25, say, above 0.21. These two conditions should get you closer to expected result.

[Anshs]

Originally Posted by vinerm

That's because there are three phases. I suggested product of volume fractions assuming there are two phases. But with three phases, even with 0.1 volume fractions of water and oil, the condition matches, despite there being 80% air. So, you have to use a condition wherein the air content is extremely low. Ideally, this would mean that the product of volume fractions of oil and water should be 0.25. But that's ideal case, not practical. So, a better approach would be to ensure that the sum of water and oil volume fraction is close to 1, say, above 0.95, as well as their product is close to 0.25, say, above 0.21. These two conditions should get you closer to expected result.

Yes, but the triangular region has th water phase there! so how is the previous surface condition getting satisfied there?

Thanks

[vinerm]

That's because the condition is for the product not to be 0, so, even if it is 0.9999 * 0.00001, it's not 0.

[Anshs]

Originally Posted by vinerm

That's because the condition is for the product not to be 0, so, even if it is 0.9999 * 0.00001, it's not 0.

Okay so basically that's because of the limit to which the solver is storing data!

Thanks!

[vinerm]

Solver stores data up to about 32 or even more decimal places.

[Anshs]

Originally Posted by vinerm

Solver stores data up to about 32 or even more decimal places.

I have written the code where 'DEFINE_ADJUST(store_gradient, domain)' is calculating the area density of the cell, so that it can be used in the 'mass transfer' expression.


1. I think I can't write the function like this inside another function.
2. Shall I separate the area function ( DEFINE_ADJUST(store_gradient, domain) ) outside the mass transfer function?

#include "udf.h"
#include "math.h"


DEFINE_MASS_TRANSFER(interface_transfer, cell, thread, from_index, from_species_index, to_index, to_species_index)

{

real m_lg;
real c_tg;
real k_g;


Thread *water = THREAD_SUB_THREAD(thread, from_index);

Thread *oil = THREAD_SUB_THREAD(thread, to_index);

m_lg = 0.0;
c_tg = 0.0;
k_g = 0.0;

if ( ( C_VOF(cell,water)*C_VOF(cell,oil) > 0.21 ) && (C_VOF(cell,water) + C_VOF(cell,oil) >0.95) )

{

k_g = 0.4 * sqrt(C_DIFF_L(cell,water,0,1)) * pow((C_D(cell,water)/ C_MU_T(cell,water)), 0.25)

c_tg = C_VOF(cell,water) * C_R(cell,water) * C_YI(cell , water , 0) ;

m_lg = k_g * (NV_MAG(C_VOF_G(c,ppt))) * ( 4e-5 - c_tg ) ;


}

else m_lg = 0.0;

return (m_lg);

}

[Anshs]

Originally Posted by Anshs

Yeah, I got your point. In the mass transfer tab of phase interaction, we will need to put on these specific details.

One more thing, if I want to further modify the transfer rate as given in the picture below.

Attachment 78037

#include "udf.h"

 

DEFINE_MASS_TRANSFER(liq_gas_source, cell, thread, from_index,

from_species_index, to_index, to_species_index)

{

   real m_lg;

   real T_SAT = 373.15;

   Thread *gas = THREAD_SUB_THREAD(thread, from_index);      // gas phase

   Thread *liq = THREAD_SUB_THREAD(thread, to_index);          // liquid phase

 

   m_lg = 0.;           // initialisation 


   if ((m_lg == 0. ) && (C_T(cell, gas) <= T_SAT))

     {

       m_lg = 0.1*C_VOF(cell,gas)*C_R(cell,gas)*

         fabs(T_SAT-C_T(cell,gas))/T_SAT;

       
         D = DEFINE_DIFFUSIVITY*(*name,*c,*t,*I)

         X_co2_eq= 0.1;

         X_co2 = C_VOF(cell,gas) * C_R(cell,gas) * C_YI(c , gas , 0)*


         k = 0.4*sqrt(D)*(C_D(c,t)/ C_MU_T(c,t)).^0.25



         //a = interfacial area/volume 

 , I have the separate UDF for this

         m_lg = k*a* ( X_co2_eq - X_co2);

         //here C_YI(c, gas, 0 ), denotes species mass fraction of 1st species in 
         the mixture denoted by phase 'gas'.

      }

   return (m_lg);

Is this correct? Thanks

Modifying this in the above thread.

[vikash0603]

I am dealing with a single phase(having two species of water and ethanol). water and ethanol are entering from two different inlets. How can I write UDFs for a single phase and multiple species?

[vikash0603]

I am dealing with a single phase(having two species of water and ethanol). water and ethanol are entering from two different inlets. How can I write UDFs for a single phase and multiple species?