mass flux at adjacent cell to wall: Hertz-Knudsen-Schrage
 

Dear all,

I want to apply the attached mass flux equation to the cells near the wall. Could someone correct my code. I have successfully applied constant heat flux value near the wall. However, applying the function seems bit tricky. Here, Pv and Tv are the vapor pressure and temperature. Pi and Ti are the temperature adjacent to the wall. Pi is calculated from Clausius-Clapeyron equation.

#include "udf.h"
int boundaryID=78;
DEFINE_ON_DEMAND(on_demand_calc)
{
real sigma;
real R=8314.40;
real M=18.015;
real hfg=2406000;
real const;
real pi;
real ti;
real pstatic=C_P(c,t);
real poper=RP_Get_Float("operating-pressure");
real pv;
real tv=C_T(c,t);
real area;
face_t f;
cell_t c;
Domain *domain=Get_Domain(1);
Thread *t;
Thread *tf
thread_loop_f(t,domain)
{
if (THREAD_ID(t)==boundaryID)
{
begin_f_loop(f,t)
{
F_AREA(area,f,t);
area =NV_MAG(area);
pi=exp(((hfg*M)/R)*((1/373.0)-(1/C_T(c0,t0))))*101325.0;
ti=sqrt(C_T(c0,t0);
pv=pstatic+poper;
const=((2*sigma)/(1-sigma))*(1/sqrt(2*3.141592653589*(R/M)));
C_UDMI(F_C0(f,t),THREAD_T0(t),0)=(const*(((pv)/tv)-(pi/ti))))*area;
}
end_f_loop(f,t)
}
}

Flux or Source
 

You cannot apply flux to the cells; you need to apply these as sources or apply at the faces instead of the cells. As far as the code is concerned, it is not applying anything; only calculating and storing in UDM. And no where is value of sigma being calculated. There is nothing called RP_Get_Float; use RP_Get_Real. There are many other syntactical mistakes in the code. It won't even compile.

Wick-vapor interface
 

Hi vinerm,
Thanks for your reply. I did things in a hurry. I have attached the corrected UDF. This is compiling successfully. However, I have some doubt. Can we use
C_P(c,t), C_T(c,t), RP_Get_Real("operating-pressure") in the star marked region below. Is this allowed?

thread_loop_f(t,domain)
{
if (THREAD_ID(t)==boundaryID)
{
begin_f_loop(f,t)
{
*****
}
end_f_loop(f,t)
}



#include "udf.h"
int boundaryID=78;
DEFINE_SOURCE(massflux1,c,t,dS,eqn)
{
real mdot;
mdot=C_UDMI(c,t,0)/C_VOLUME(c,t);
return (mdot);
}
DEFINE_ON_DEMAND(on_demand_calc)
{
face_t f;
cell_t c;
cell_t c0;
Domain *domain=Get_Domain(1);
Thread *t;
Thread *t0;
real sigma=0.03;
real R=8314.40;
real M=18.015;
real hfg=2406000;
real pi;
real ti;
real pstatic=C_P(c,t);
real poper=RP_Get_Real("operating-pressure");
real pv;
real tv;
real A[ND_ND];
real area;
thread_loop_c(t,domain)
{
begin_c_loop(c,t)
{
C_UDMI(c,t,0)=0;
}
end_c_loop(c,t)
}
thread_loop_f(t,domain)
{
if (THREAD_ID(t)==boundaryID)
{
begin_f_loop(f,t)
{
c0=F_C0(f,t);
t0=THREAD_T0(t);
F_AREA(A,f,t);
area=NV_MAG(A);
pi=exp(((hfg*M)/R)*((1/373.0)-(1/C_T(c0,t0))))*101325.0;
ti=sqrt(C_T(c0,t0));
pstatic=C_P(c,t);
pv=pstatic+poper;
tv=C_T(c,t);
C_UDMI(c0,t0,0)=(((2*sigma)/(1-sigma))*(1/sqrt(2*3.141592653589*(R/M)))*((pv/tv)-(pi/ti)))*area;
}
end_f_loop(f,t)
}
}
}

What do you mean by applying flux at face? Is it possible to apply flux without DEFINE_SOURCE. I thought DEFINE_SOURCE is the only way for this problem. I would like to know more about applying flux directly at the face. May be it is more relevant for my problem. I am not able to achieve the expected results using DEFINE_SOURCE. I will try both the methods simultaneously. Thank you for your kind help.

What do you mean by applying flux at face? Is it possible to apply flux without DEFINE_SOURCE. I thought DEFINE_SOURCE is the only way for this problem. I would like to know more about applying flux directly at the face. May be it is more relevant for my problem. I am not able to achieve the expected results using DEFINE_SOURCE. I will try both the methods simultaneously. Thank you for your kind help.

Source and Flux
 

DEFINE_SOURCE is NOT used for defining flux, but for source. Flux and source are different, though inter-convertible using Gauss' theorem. If you want to apply flux, use DEFINE_PROFILE.