surface reaction UDF
 

hey！i am modelling the surface reaction，the overal reaction equation：2O3 -> 3O2. and its reaction rate formular is: r = K*b*O3/(1+b*O3); my UDF code as follows：
#include "udf.h"
#define K 6.8586e-11
#define b 15296.9e3
DEFINE_SR_RATE(my_rate,f,t,r,mw,yi,rr)
{
Thread *t0 = t->t0;
cell_t c0 = F_C0(f,t);
real o3 = yi[0];
real rho_w = 1.0, T_w = 300.0;
T_w = F_T(f,t);
rho_w = C_R(c0,t0)*C_T(c0,t0)/T_w;
o3 *=rho_w/mw[0];
*rr = K*b*o3/(1+b*o3);
}

the problem is：after compile and hook the UDF，the calcucation results showed that the reaction rate on the defined surface was zero。is there anyone who can help me analyse where the problem is and how to solve it? thanks!

The *rr calculated is in order of 10^-8 , isnt that too low?

I have adjust the accurance of the reaction rate, the order of 10^-8 can be displayed!