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[894875960]

Hi, guys. I'm trying to simulate a liquid-solid catalytic reaction, coulped with the multiphase flow. The liquid reactants transfer into the solid phase and the chemical reaction subsequently occurs in the solid phase. Euler methods are used to describe the liquid-solid multiphase flow, and there are more than two species in liquid phase. I have noticed that all relevant references give the reaction rate  R in relation to the liquid phase concentration, such as R = K·c1·c2, where c1, c2 represent the molar concentration in liquid phase. However! If I attain the concentration by C_YI(c, t, 0) when add mass source term for solid phase, the C_YI(c, t, 0) represents the concentration in solid phase, and this is not consistent with the formula. Does anyone know how to deal this? 

I've attached the codes from the UDF manual, but haven't found the way to get concentrations in other phase. Or maybe I'm just not understanding the code？

 

[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