Is it possible to model a reversible surface reaction, for example A <-> B? The option is enabled in fluent5 but disabled in fluent6, which leads me to believe that it was not working in fluent5. I have tried creating two wall reactions, i.e. A -> B and B -> A at the same wall using UDF:

DEFINE_SR_RATE { if (!strcmp(r->name, "reaction-1")) { printf ("Reaction 1 being executed"); *rr = 500;} /* or any other value */ if (!strcmp(r->name, "reaction-2")) { printf ("Reaction 2 being executed"); *rr = 500;} /* or any other value */ }

When run, the value for reaction-1 can be used to vary the species concentration whereas the value in reaction-2 has no effect. Also the message that reaction is being executed does not appear.

Any help would be gratefully received.

It seems that the UDF is never beign called with "reaction-2". Try to put this...

Message("%s\n",r->name); at the top of the UDF to see the reaction name.

Thanks for the help, I am trying that right now. I also through a face =%d in the massage so I could see what face number it was accessing. For each iteration it prints reaction-1 for all the faces on all of the iterations, so is it not recognisng the second reaction I explicity specified in the Fluent GUI? Also here is another question about the reaction model that may be a way around the problem: The rate of creation/destruction of species is given by: R = k [conc] when you set *rr in the SR_RATE UDF are you setting k or k[conc]? I assumed it was k but in the UDF manual section 4.3.16 there was this example:

DEFINE_SR_RATE(my_rate, f, t, r, mw, yi, rr) { Thread *t0=t->t0; cell_t c0=F_C0(f,t); real sih4 = yi[0]; /* mass fraction of sih4 at the wall */ real si2h6 = yi[1]; real sih2 = yi[2]; real h2 = yi[3]; real ar = yi[4]; /* mass fraction of ar at the wall */

real rho_w = 1.0, site_rho = 1.0e-6, T_w = 300.0;

real si_s = yi[6]; /* site fraction of si_s*/ real sih_s = yi[7]; /* site fraction of sih_s*/

T_w = F_T(f,t); rho_w = C_R(c0,t0)*C_T(c0,t0)/T_w;

sih4 *= rho_w/mw[0]; /* converting of mass fractions to molar concentrations */ si2h6 *= rho_w/mw[1]; sih2 *= rho_w/mw[2]; h2 *= rho_w/mw[3]; ar *= rho_w/mw[4];

si_s *= site_rho; /* converting of site fractions to site concentrations */ sih_s *= site_rho;

if (STREQ(r->name, "reaction-1"))

*rr = 100.0*sih4; else if (STREQ(r->name, "reaction-2"))

*rr = 0.1*sih_s; else if (STREQ(r->name, "reaction-3"))

*rr = 100*si2h6*si_s; else if (STREQ(r->name, "reaction-4"))

*rr = 1.0e10*sih2;

}

where the concentrations are put in explicity. Any advise on this matter would be apprciated.