[Hello_Wang]

Hello everyone,

I am new to Ansys fluent and UDF programming. So, I have been confused with the UDF which can deal with the gas dissolution in DPM droplets for a long time.
For my case, I want to calculate CO2 dissolution ( mass transfer rate, total mass transfer of CO2) in the water droplets, of which water droplets were modeled with DPM, CO2 and air are continuous phases.
I have read the user guide documents and almost all the examples on the forum, but I still have not solved my problem.
Maybe my question is foolish, but I still hope you can kindly answer me. I have done my best.
(1) DEFINE_DPM_HEAT_MASS, or DEFINE_DPM_SOURCE, which one is more suitable for my case?
(2) I have spent a lot of time on DEFINE_DPM_HEAT_MASS, but fluent crashed when runs with this UDF.

#include "udf.h"
#include "dpm.h"
#include "dpm_mem.h"

#define R 8.314; /* gas constant [J/K/mol] */

DEFINE_DPM_HEAT_MASS(absorp, tp, Cp, hgas, hvap, cvap_surf, Z, dydt, dzdt)
{
int CO2_index = 3; /* index of CO2 species in mixture material*/
real MW_CO2 = 44.01e-3; /* Molecular mass of CO2 [kg/mol] */

int ns; // species index
Material *sp; // speices pointer
real dens_total = 0.0; /* total vapor density*/
real P_total = 0.0; /* vapor pressure */
int nc = TP_N_COMPONENTS(tp); /* number of particle components */
Thread *t0 = TP_CELL_THREAD(tp); /* thread where the particle is in*/

Material *gas_mix = THREAD_MATERIAL(DPM_THREAD(t0, tp)); /* gas mixture material */
Material *cond_mix = TP_MATERIAL(tp); /* particle mixture material*/
cphase_state_t *c = &(tp->cphase[0]); /* cell information of particle location*/

cell_t c0 = P_CELL(tp); /*cell where the particle is in*/

real molwt[MAX_SPE_EQNS]; /* molecular weight of gas species */
real Tp = TP_T(tp); /* particle temperature */
real mp = TP_MASS(tp); /* particle mass */
real molwt_bulk = 0.; /* average molecular weight in bulk gas */
real Dp = DPM_DIAM_FROM_VOL(mp / TP_RHO(tp)); /* particle diameter */
real Ap = DPM_AREA(Dp); /* particle surface */
real Pr = c->sHeat * c->mu / c->tCond; /* Prandtl number */
real Nu = 2.0 + 0.6 * sqrt(tp->Re) * pow(Pr, 1. / 3.); /* Nusselt number */
real h = Nu * c->tCond / Dp; /* Heat transfer coefficient*/
real dh_dt = h * (c->temp - Tp) * Ap; /* heat source term*/
dydt[0] += dh_dt / (mp * Cp); // particle temperature [K/s]
C_UDMI(TP_CELL(tp), TP_CELL_THREAD(tp), 0) = dydt[0];
dzdt->energy -= dh_dt; // gas phase enthalpy [J/s]
C_UDMI(TP_CELL(tp), TP_CELL_THREAD(tp), 1) = dzdt->energy;

// Loop over all of the species for the given mixture material
mixture_species_loop(gas_mix, sp, ns)
{
molwt[ns] = MATERIAL_PROP(sp, PROP_mwi); /* molecular weight of gas species */
molwt_bulk += c->yi[ns] / molwt[ns]; /* average molecular weight */
}
/* prevent division by zero */
molwt_bulk = MAX(molwt_bulk, DPM_SMALL);
C_UDMI(TP_CELL(tp), TP_CELL_THREAD(tp), 2) = molwt_bulk;

real yi_CO2_L;
// for (ns = 0; ns < nc; ns++)
/* CO2 dissolved in the water droplets */
for (yi_CO2_L = 0; yi_CO2_L < 1; ++TP_COMPONENT_I(tp, ns))
{
real Tm = C_T(TP_CELL(tp), TP_CELL_THREAD(tp)); /* mean Temperature [K] */
real yi_CO2_g = C_YI(TP_CELL(tp), TP_CELL_THREAD(tp), CO2_index); /* CO2 mass fraction in gas phase */

real dens_g = C_R(TP_CELL(tp), TP_CELL_THREAD(tp)); /* density of mixture or gas phase */

real C_CO2_g = yi_CO2_g * dens_g / MW_CO2; /* Molar concentration of CO2 in gas phase [mol/m3] */
real P_CO2_g = C_CO2_g * 8.314 * Tm; /* partial pressure of CO2 in gas phase */
real dens_L = P_RHO(tp); /* denisty of droplets */
real C_CO2_L = yi_CO2_L * dens_L / MW_CO2; /* molar concentration of CO2 in droplet [mol/m3] */
real He = 3.54e-7 * exp(2044 / Tm); /*Henry Constant for CO2 in the pure water, [mol/(m3*Pa)], Versteeg et al, 1988*/

real V = NV_MAG(P_VEL(tp)); /* water droplet velocity*/
real vg = 15.69e-6; /* kninematic viscosity of air [m2/s] */
real Re = Dp * V / vg;
real Df = 2.35e-6 * exp(-2119 / Tm); /* CO2 molecular diffisivity in water */
real Sc = vg / Df;

real kL = 2.0 + 0.6 * sqrt(Re) * pow(Sc, 1. / 3.); /*mass transfer coefficient in liquid phase*/
real NA = kL * (P_CO2_g - He * C_CO2_L); /*Mass transfer flux of CO2, [mol/m2/s] */
/* concentration difference * mass transfer coefficient */
real NA_rate = NA * MW_CO2 * Ap; // [kg/s]

dydt[2] += NA_rate;
dzdt->species[CO2_index] -= NA_rate;
}
return;
}

(3) More detailly, how can I iterate or calculate the CO2 concentration dissolved in water droplets in each time step? I am not sure about this.
Any help or suggestion, I will be appreciated it.
Thanks a lot

[minzhang]

Hi Aijuan, I am wondering whether you have solved your problem and whether you can share with me some learnings. I want to do HCl (in the continuum gas phase) dissolution in the water droplets. Thanks a lot!!