[vidyadhar]

Hi Everyone,

Taking the help of online forums, I have managed to write an UDF that predicts evaporation mass/heat flux at the vapor-liquid interface using VOF method of Fluent.The evaporation flux equation is Hertz-Knudsen-Schrage Equation simplified according to Tanasawa's linearization as mentioned in Hardt and Wondra, J.Compt.Physics 227(2008) 5871-5895.


But, I am facing problems in validating this UDF with literature such as Stefan Problem. Stefan problem involves movement of the interface between a superheated vapor and saturated liquid due to the evaporation of liquid; heat being supplied from a hot wall through the vapor phase.


By running the following UDF, the interface is moving but with higher speed than predicted by analytical solution of Stefan problem. I request anyone to help me- if there is any mistake in the UDF code.


*******************************************
*******************************************

#include "udf.h"
#define T_SAT 373.15


/*to store gradient of volume fraction of primary phase, DEFINE_ADJUST macro has been used*/


DEFINE_ADJUST(my_adjust, mixture_domain)
{
int phase_domain_index=0.;
Thread *t;
Thread **pt;
cell_t c;

Domain *pDomain = DOMAIN_SUB_DOMAIN(mixture_domain,phase_domain_inde x);
{
Alloc_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_N ULL);
Scalar_Reconstruction(pDomain, SV_VOF,-1,SV_VOF_RG,NULL);
Scalar_Derivatives(pDomain,SV_VOF,-1,SV_VOF_G,SV_VOF_RG,Vof_Deriv_Accumulate);
}

mp_thread_loop_c (t,mixture_domain,pt)
if (FLUID_THREAD_P(t))
{
Thread *ppt = pt[phase_domain_index];

begin_c_loop (c,t)
{
C_UDMI(c,t,0)=NV_MAG(C_VOF_G(c,ppt));
}
end_c_loop (c,t)
}
Free_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_NU LL);

}



/*This macro is used to apply mass and heat exchange between vapor and liquid phases*/

DEFINE_MASS_TRANSFER(liq_gas_source,c,t,from_index ,from_species_index,to_index,to_species_index)
{
Thread *gas=THREAD_SUB_THREAD(t,to_index);
Thread *liq=THREAD_SUB_THREAD(t,from_index);
real source;
if (C_VOF(c,liq)!=0.0 && C_VOF(c,liq)!=1.0 && C_UDMI(c,t,0)!=0)
{
source=5.150461258e-05*(C_T(c,t)-T_SAT)*(C_UDMI(c,t,0)); /*mass transfer rate flux = constant X (Ti-Tsat); Ti is interface temperature */
return source;
}
}





Thanks in advance!
Vidyadhar

[saddy]

i dont know anything about udf
however, i think fluent does have rpi boiling model
why not use that?

[mohibanwar]

Originally Posted by vidyadhar

Hi Everyone,

Taking the help of online forums, I have managed to write an UDF that predicts evaporation mass/heat flux at the vapor-liquid interface using VOF method of Fluent.The evaporation flux equation is Hertz-Knudsen-Schrage Equation simplified according to Tanasawa's linearization as mentioned in Hardt and Wondra, J.Compt.Physics 227(2008) 5871-5895.


But, I am facing problems in validating this UDF with literature such as Stefan Problem. Stefan problem involves movement of the interface between a superheated vapor and saturated liquid due to the evaporation of liquid; heat being supplied from a hot wall through the vapor phase.


By running the following UDF, the interface is moving but with higher speed than predicted by analytical solution of Stefan problem. I request anyone to help me- if there is any mistake in the UDF code.


*******************************************
*******************************************

#include "udf.h"
#define T_SAT 373.15


/*to store gradient of volume fraction of primary phase, DEFINE_ADJUST macro has been used*/


DEFINE_ADJUST(my_adjust, mixture_domain)
{
int phase_domain_index=0.;
Thread *t;
Thread **pt;
cell_t c;

Domain *pDomain = DOMAIN_SUB_DOMAIN(mixture_domain,phase_domain_inde x);
{
Alloc_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_N ULL);
Scalar_Reconstruction(pDomain, SV_VOF,-1,SV_VOF_RG,NULL);
Scalar_Derivatives(pDomain,SV_VOF,-1,SV_VOF_G,SV_VOF_RG,Vof_Deriv_Accumulate);
}

mp_thread_loop_c (t,mixture_domain,pt)
if (FLUID_THREAD_P(t))
{
Thread *ppt = pt[phase_domain_index];

begin_c_loop (c,t)
{
C_UDMI(c,t,0)=NV_MAG(C_VOF_G(c,ppt));
}
end_c_loop (c,t)
}
Free_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_NU LL);

}



/*This macro is used to apply mass and heat exchange between vapor and liquid phases*/

DEFINE_MASS_TRANSFER(liq_gas_source,c,t,from_index ,from_species_index,to_index,to_species_index)
{
Thread *gas=THREAD_SUB_THREAD(t,to_index);
Thread *liq=THREAD_SUB_THREAD(t,from_index);
real source;
if (C_VOF(c,liq)!=0.0 && C_VOF(c,liq)!=1.0 && C_UDMI(c,t,0)!=0)
{
source=5.150461258e-05*(C_T(c,t)-T_SAT)*(C_UDMI(c,t,0)); /*mass transfer rate flux = constant X (Ti-Tsat); Ti is interface temperature */
return source;
}
}





Thanks in advance!
Vidyadhar

Hello Vidya dhar,
Are you sure this UDF is working in your problem without any Energy source?

[vidyadhar]

Hi,
I understand that the macro DEFINE_MASS_TRANSFER will account for mass and energy source terms in the respective equations. In that way, it should estimate energy sources.

However, I could not get the desired result by using the above UDF and I am still working on it.


Thanks & Regards,

Vidyadhar

[ruiarahul]

Originally Posted by vidyadhar

Hi Everyone,

Taking the help of online forums, I have managed to write an UDF that predicts evaporation mass/heat flux at the vapor-liquid interface using VOF method of Fluent.The evaporation flux equation is Hertz-Knudsen-Schrage Equation simplified according to Tanasawa's linearization as mentioned in Hardt and Wondra, J.Compt.Physics 227(2008) 5871-5895.


But, I am facing problems in validating this UDF with literature such as Stefan Problem. Stefan problem involves movement of the interface between a superheated vapor and saturated liquid due to the evaporation of liquid; heat being supplied from a hot wall through the vapor phase.


By running the following UDF, the interface is moving but with higher speed than predicted by analytical solution of Stefan problem. I request anyone to help me- if there is any mistake in the UDF code.


*******************************************
*******************************************

#include "udf.h"
#define T_SAT 373.15


/*to store gradient of volume fraction of primary phase, DEFINE_ADJUST macro has been used*/


DEFINE_ADJUST(my_adjust, mixture_domain)
{
int phase_domain_index=0.;
Thread *t;
Thread **pt;
cell_t c;

Domain *pDomain = DOMAIN_SUB_DOMAIN(mixture_domain,phase_domain_inde x);
{
Alloc_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_N ULL);
Scalar_Reconstruction(pDomain, SV_VOF,-1,SV_VOF_RG,NULL);
Scalar_Derivatives(pDomain,SV_VOF,-1,SV_VOF_G,SV_VOF_RG,Vof_Deriv_Accumulate);
}

mp_thread_loop_c (t,mixture_domain,pt)
if (FLUID_THREAD_P(t))
{
Thread *ppt = pt[phase_domain_index];

begin_c_loop (c,t)
{
C_UDMI(c,t,0)=NV_MAG(C_VOF_G(c,ppt));
}
end_c_loop (c,t)
}
Free_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_NU LL);

}



/*This macro is used to apply mass and heat exchange between vapor and liquid phases*/

DEFINE_MASS_TRANSFER(liq_gas_source,c,t,from_index ,from_species_index,to_index,to_species_index)
{
Thread *gas=THREAD_SUB_THREAD(t,to_index);
Thread *liq=THREAD_SUB_THREAD(t,from_index);
real source;
if (C_VOF(c,liq)!=0.0 && C_VOF(c,liq)!=1.0 && C_UDMI(c,t,0)!=0)
{
source=5.150461258e-05*(C_T(c,t)-T_SAT)*(C_UDMI(c,t,0)); /*mass transfer rate flux = constant X (Ti-Tsat); Ti is interface temperature */
return source;
}
}





Thanks in advance!
Vidyadhar

you seem to be pretty knowledgeable in multiiphase simulations, can you please help me with simulating capillary effect in a wick region?

[vidyadhar]

Hello Rahul,


I have just started learning multiphase flows. Currently I am not fully involved in it. In future I may study them at length.

I do not know about the simulation of capillary effect etc.

You may please take the help of experts in that area.


Thanks & Regards,
Vidyadhar

[soumitra2102]

Hi Vidyadhar,

Can this UDF be useful for simulating condensation phenomenon as well?

If not, then can you please suggest me anything?
Fluent's VoF+Evapo-Conden model did not gave me any considerable condensaton volume fraction.

Thanks

-Soumitra

[vidyadhar]

Hello Soumitra,
I think it should be valid for condensation as well.
You may have to slightly modify the UDF to suit the physics of condensation.
Once it is validated with some proven results, you can rely on it.
As of now, it just works. But, it should be validated.


All the best!
vidyadhar

[sshivam]

Hello,
can anyone please guide regarding the UDF that saves the time value for a cell when the volume fraction becomes 1. I am using VOF method.

Thanks