Reply To: Mass Source Term UDF of Chemical Reaction

[jcooper]

 

 

Hi:

In Multiphase, phase species are stored under the phase thread, so they must be called as

C_YI(c,tp,species_index), where tp is the phase thread and species_index is the number of the specie (from 0-N-1) in the given phase. (The secondary phase thread could be defined as ts.)

The declaration of the phase threads would be as for DEFINE_HET_RXN_RATE below, which is written for multiphase phase change:

 

 

DEFINE_HET_RXN_RATE(user_evap_condens_react, c, t, hr, mw, yi, rr, rr_t)
 {
 #define index_evap_primary 0 /*evaporating species index in primary phase*/
 #define prim_index 0 /*index of primary phase*/
    Thread **pt = THREAD_SUB_THREADS(t);
    Thread *tp = pt[0];
    Thread *ts = pt[1];
    int i;
    real concentration_evap_primary, accum = 0., mole_frac_evap_prim,
     concentration_sat ;
    real T_prim = C_T(c,tp); /*primary phase (gas) temperature*/
    real T_sec = C_T(c,ts); /*secondary phase (droplet) temperature*/
    real diam = C_PHASE_DIAMETER(c,ts); /*secondary phase diameter*/
    real D_evap_prim = C_DIFF_EFF(c,tp,index_evap_primary)
      - 0.7*C_MU_T(c,tp)/C_R(c,tp);

     /*primary phase species turbulent diffusivity*/
    real Re, Sc, Nu, urel, urelx,urely,urelz=0., mass_coeff, area_density,
       flux_evap ;

    if(Data_Valid_P())
      {
         urelx = C_U(c,tp) - C_U(c,ts);
         urely = C_V(c,tp) - C_V(c,ts);

         #if RP_3D
           urelz = C_W(c,tp) - C_W(c,ts);
         #endif

         urel = sqrt(urelx*urelx + urely*urely + urelz*urelz);
         /*relative velocity*/

        Re = urel * diam * C_R(c,tp) / C_MU_L(c,tp);
        Sc = C_MU_L(c,tp) / C_R(c,tp) / D_evap_prim ;
        Nu = 2. + 0.6 * pow(Re, 0.5)* pow(Sc, 0.333);
        mass_coeff = Nu * D_evap_prim / diam ;
        for (i=0; i < MAX_SPE_EQNS_PRIM ; i++)
         {
           accum = accum + C_YI(c,tp,i)/mw[i][prim_index];
         }
        mole_frac_evap_prim = C_YI(c,tp,index_evap_primary)
           / mw[index_evap_primary][prim_index] / accum;
        concentration_evap_primary = mole_frac_evap_prim * P_OPER
           / UNIVERSAL_GAS_CONSTANT / T_prim ;
        concentration_sat = psat_h2o(T_sec)/UNIVERSAL_GAS_CONSTANT/T_sec ;
        area_density = 6. * C_VOF(c,ts) / diam ;
        flux_evap = mass_coeff *
            (concentration_sat - concentration_evap_primary) ;
        *rr = area_density * flux_evap ;
      } 
} 

 

The above UDF example was taken from the Fluent Customization Manual here:

https://ansyshelp.ansys.com/Views/Secured/corp/v242/en/flu_udf/flu_udf_MultiphaseDEFINE.html#flu_udf_sec_define_het_rxn_rate

Regards,

Judy