[tahar]

hi gues
During modeling of water evaporation below boiling point (between 30 to 40°c) i use FLUENT UDF to model diffusion where the saturated pressure is calculated using this expression

real T = C_T(cell, liq);
P_SAT = exp(77.345 + 0.0057*T - 7235 / T) / pow(T, 8.2);

then i use the saturated pressure to calculte the vapor partial pressure

via this expression


real p_vap =P_SAT *(MWair/(MWair+MWvapor*(1/mf_vapor-1))) ;


MWair molecal weight of air

MWair molecal weight of vapor

mf_vapor vapor mass fraction = C_YI(cell, vap,0) fluent macro


IS THIS correct ????

and how i can get relative humidity if i now mass fraction and molecal weight ??

[tahar]

any suggestions please

[aero_head]

Hello,
To your first question, there are some threads on here about that, like so: how to obtain mass diffusion coefficient with UDF?
Your second question is a really basic thermodynamics problem. You can read up on the relevant topics online, here's an example: https://www.learnthermo.com/examples...on=D&problem=9

[tahar]

Originally Posted by aero_head

Hello,
To your first question, there are some threads on here about that, like so: how to obtain mass diffusion coefficient with UDF?
Your second question is a really basic thermodynamics problem. You can read up on the relevant topics online, here's an example: https://www.learnthermo.com/examples...on=D&problem=9

TANK YOU FOR YOUR HELP
MY problem is with vapor pressure and where the displayed value is not expected at all My UDF FOR MASS TRANSFERT is based on CARRIES EQUATION :

any help will be very appreciated

DEFINE_LINEARIZED_MASS_TRANSFER(cav_source, cell, thread, from_index, from_species_index, to_index, to_species_index, d_mdot_d_vof_from, d_mdot_d_vof_to)
{
Thread *liq = THREAD_SUB_THREAD(thread, from_index);
Thread *vap = THREAD_SUB_THREAD(thread, to_index);


real T = C_T(cell, liq),P_SAT = exp(77.345 + 0.0057*T - 7235 / T) / pow(T, 8.2);


real m_dot=0.0, dp, m_source=0.0, p_op = RP_Get_Real("operating-pressure");


real rho_v = C_R(cell, vap),rho_l = C_R(cell, liq);

real vof_l = C_VOF(cell, liq);


real vof_v = 1.0 - vof_l;

real r_rho_lv = 1. / rho_v - 1. / rho_l,

h_fg = 2437426.07;


/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/

real p_vap = (C_P(cell, thread) + p_op);

//real p_vap = (C_P(cell, thread) + p_op)*(28.96/(28.96+18.01*(1/mf_vapor-1))) ;

//real p_vap =P_SAT *(28.96/(28.96+18.01*(1/mf_vapor-1))) ;



real vel = sqrt(C_U(cell, thread)*C_U(cell, thread) + C_V(cell, thread)*C_V(cell, thread));

if (p_vap <= P_SAT)
{
dp = P_SAT - p_vap;
dp = MAX(dp, 1e-4);
m_dot = (0.0888 + 0.0783*vel)* dp / h_fg;
m_source = m_dot*vof_l;

C_UDMI(cell, thread, 1) = m_source;
C_UDMI(cell, thread, 2) = P_SAT;
C_UDMI(cell, thread, 3) = p_vap;

C_UDMI(cell, thread, 5) = vof_v;

C_UDMI(cell, thread, 7) = vof_l;

*d_mdot_d_vof_from = m_dot;
*d_mdot_d_vof_to = -m_dot;
}
else
{ dp = P_SAT - p_vap; dp = MAX(dp, 1e-4); m_dot = 0.0; m_source = m_dot*vof_l;

C_UDMI(cell, thread, 2) = P_SAT;
C_UDMI(cell, thread, 3) = p_vap;

C_UDMI(cell, thread, 5) = vof_v;

C_UDMI(cell, thread, 7) = vof_l;

C_UDMI(cell, thread, 1) = m_source; *d_mdot_d_vof_from = m_dot;
*d_mdot_d_vof_to = -m_dot;
}
if (NNULLP(THREAD_STORAGE(thread, SV_MT_DS_DP)))
C_STORAGE_R(cell, thread, SV_MT_DS_DP) = ABS(r_rho_lv*m_source / dp);
return m_source;
}


any help will be very appreciated

[tahar]

PLEASE i need helps from mass transfert expert

[fard734]

Dear Tahar
I hope you I doing well, I know this post is so old, but I would like to know if you got the results using this UDF/