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UDF for multicomponent particle

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February 8, 2012, 20:55 UDF for multicomponent particle vaporization #1

MohsinSenior Member

Mohsin Mukhtar

Join Date: Mar 2010Location: South KoreaPosts: 249Rep Power: 6

I have coal par cles surrounded by liquid water (hence mul -component). As soon as

the wet coal will enter into the domain, the liquid water will evaporate into vapors and

dry coal will exit the domain.

FLUENTs inbuilt code only supports droplet (1 component) vaporiza on. Hence, UDF

has to be wri en for mul -component par cles. Fortunately, Fluent has provided a UDF

code to solve mul -component vaporiza on in the following link:

h p://hpce.iitm.ac.in/website/Manuals/Fluent_6.3/fluent6.3/help/html

/udf/node64.htm

However, when I compile and hook the above UDF in DPM model of FLUENT and run

the simula on, I get 0 evapora on of water. I think, there is some problem in the code

and modifica ons have to be done in the code, as there is no men oning of

vaporiza on that should start when Tp>=vap-temp

The following is the same UDF code as was seen in the link above but boiling por on is

neglected(as there is no boiling in my case). Could anyone please explain what should

be added here to get vaporiza on of water from coal par cles?

/***********************************************************************UDF for defining the heat and mass transport formulticomponent particle vaporization***********************************************************************/

for multicomponent particle vaporization -- CFD Online Discussion ... http://www.cfd-online.com/Forums/fluent-udf/97102-udf-multicom

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#include "udf.h"

DEFINE_DPM_HEAT_MASS(multicomponent_vaporization,p,Cp,hgas,hvap,cvap_surf,Z,dydt,dzdt){int ns;Material *sp;real dens_total = 0.0; /* total vapor density*/real P_total = 0.0; /* vapor pressure */int nc = TP_N_COMPONENTS(p); /* number of particle components

*/Thread *t0 = P_CELL_THREAD(p); /* thread where the particleis in */Material *gas_mix = THREAD_MATERIAL(DPM_THREAD(t0, p)); /*gas mixture material */Material *cond_mix = P_MATERIAL(p); /* particle mixturematerial*/cphase_state_t *c = &(p->cphase); /* cell information ofparticle location*/real molwt[MAX_SPE_EQNS]; /* molecular weight of gas species*/real Tp = P_T(p); /* particle temperature */real mp = P_MASS(p); /* particle mass *//*..............................................*/real molwt_bulk = 0.; /* average molecular weight in bulk gas*/real Dp = DPM_DIAM_FROM_VOL(mp / P_RHO(p)); /* particlediameter */real Ap = DPM_AREA(Dp); /* particle surface */real Pr = c->sHeat * c->mu / c->tCond; /* Prandtl number */real Nu = 2.0 + 0.6 * sqrt(p->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);dzdt->energy -= dh_dt;

mixture_species_loop(gas_mix,sp,ns){molwt[ns] = MATERIAL_PROP(sp,PROP_mwi); /* molecular weightof gas species */molwt_bulk += c->yi[ns] / molwt[ns];}/* prevent division by zero */molwt_bulk = MAX(molwt_bulk,DPM_SMALL);

for (ns = 0; ns < nc; ns++){int gas_index = TP_COMPONENT_INDEX_I(p,ns); /* average

molecular weight */if( gas_index >= 0 ){/* condensed material */Material * cond_c = MIXTURE_COMPONENT(cond_mix, ns);/* vaporization temperature */real vap_temp = MATERIAL_PROP(cond_c,PROP_vap_temp);/* diffusion coefficient */real D = MATERIAL_PROP_POLYNOMIAL(cond_c,PROP_binary_diffusivity, c->temp);/* Schmidt number */


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real Sc = c->mu / ( c->rho * D );/* mass transfer coefficient */real k = (2. + 0.6 * sqrt(p->Re) * pow(Sc, 1./3.)) * D / Dp;/* bulk gas concentration (ideal gas) */real cvap_bulk = c->pressure / UNIVERSAL_GAS_CONSTANT /c->temp* c->yi[gas_index] / molwt_bulk/solver_par.molWeight[gas_index];

/* vaporization rate */real vap_rate = k * molwt[gas_index] * Ap* (cvap_surf[ns] - cvap_bulk);

/* no vaporization below vaporization temperature, nocondensation*/if (Tp < vap_temp || vap_rate < 0.0)vap_rate = 0.;

dydt[1+ns] -= vap_rate;dzdt->species[gas_index] += vap_rate;/* dT/dt = dh/dt / (m Cp)*/dydt[0] -= hvap[gas_index] * vap_rate / ( mp * Cp );

/* gas enthalpy source term */dzdt->energy += hgas[gas_index] * vap_rate;

P_total += cvap_surf[ns];dens_total += cvap_surf[ns] * molwt[gas_index];}}}

Last edited by Mohsin; February 9, 2012 at02:50.

September 27, 2012, 01:16 #2

SujalaNew Member

Sujala BhattaraiJoin Date: Sep 2012Posts: 2Rep Power: 0

Hi, How did u solve this problem. I am also doing CFD simulation of pneumatic

dryer. I followed your thread and used the multicomponent droplet (particles +

water). And used the UDF Define_DPM_HEAT_MASS. And couldn't see any

evaporation. I am student from KNU, south korea.

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