[PaRa]

Hi,
I´d like to calculate the phase change mass transfer of condensating water vapor using a UDF.
The UDF is compiled and loaded without error, but it doesnt seem to work properly.
When i print the calculated saturation temperature its only returning the value "-109.8".
I think there is something wrong with the way I try to get the relative humidity.
Any ideas, how i have to change the UDF, or maybe another aproach i could try?

Thanks in advance!

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


/* Humidity */
real H2O_Saturation_Pressure(real T)
{
real pot;
real psat;
pot = exp((17.62*(T-273.15))/(243.12+(T-273.15))); /* T in °C */
psat = 611.2 * pot;
return psat;
}

real myHumidity(cell_t c, Thread *t)
{
int i;
Material *m = THREAD_MATERIAL(t), *sp;
real yi_h2o = 0; /* water mass fraction */
real r_mix = 0.0; /* sum of [mass fraction / mol. weight] over all species */
int h2o_index = 0;
real mw_h2o = 18.01534;
real humidity;

if ((MATERIAL_TYPE(m) == MATERIAL_MIXTURE) && (FLUID_THREAD_P(t)))
{
yi_h2o = C_YI(c, t, h2o_index); /* water vapor mass fraction */
mixture_species_loop(m, sp, i)
{
r_mix += C_YI(c,t,i) / MATERIAL_PROP(sp, PROP_mwi);
}

humidity = op_pres * yi_h2o / (mw_h2o * r_mix) / H2O_Saturation_Pressure(C_T(c,t));
return humidity;
}
else
return 0.;

}

DEFINE_MASS_TRANSFER(cond, c, t, from_index, from_species_index, to_index, to_species_index)
{


/* T_SAT & Masstranser */

real m_lg;
real T_SAT;
Thread *vap;
Thread *liq;
vap = THREAD_SUB_THREAD(t, from_index);
liq = THREAD_SUB_THREAD(t, to_index);
m_lg = 0.0;

T_SAT = pow(relative_humidity(c,t), 0.124688279)*(109.8+C_T(c,t))-109.8;
if (C_T(c, liq) > T_SAT)
{ /* Evaporating */
m_lg = -0.1*C_VOF(c,liq)*C_R(c,liq)*(C_T(c,liq)-T_SAT)/T_SAT;
}

else if (C_T(c,vap) < T_SAT)
{ /* Condensing */
m_lg = 0.1*C_VOF(c,vap)*C_R(c,vap)*(T_SAT-C_T(c,vap))/T_SAT;
}
Message("T_SAT: %g\n",T_SAT);

return (m_lg);

}