If your H2 concentration is not decreasing you probably don't have much reaction taking place.  Take a closer look at your reaction  rate constants and reaction rates to see if they are off by an order of magnitude or more.

Thank you for your response Rick

Well I adjusted my UDF to higher constant values of reaction rates (i.e., .01 or even higher). But I still don't see any changes in hydrogen concentration, or increase in CH4 mass fraction. I am so confused why there is a reaction rate, the mass fractions remain unchanged.

Check that H2 really is a reactany  (not a simple misspelled component  if the rearants look right keep changing the reaction rate constan by a factor of ten until some h2 actually reacts.  Make sure you aren't changing the wrong reactionor that it isn't set to 0 rate someplace else  and that all of the components are actually  correct. You could have a typo on your reaction definiton or a component

 If you have a bogus reactant with  0 rate your reaction will not occur.  

Hi I'm simulating a heterogeneous reaction between two phases in Eulerian multiphase model, for liquid metal oxidation. Do I need to write UDF function to have the reaction or I can use the phase interaction tab to set the reaction rate? Because I use the phase interaction and set the rate of reaction with Arrhenius rate and no reaction happens? Please advice

Hussein:

You need to write a UDF. I see reactions in my case, but my problem is no mass fraction changes occurs 

Thanks Hossein, I write the below UDF but I get an error while complied. Frankly I don't have enough experience with C language can you please advice:

Thanks  

#include "udf.h"

static const real Arrhenius = 1.e15; static const real E_Activation = 1.e6; #define SMALL_S 1.e-29

DEFINE_HET_RXN_RATE(arrh,c,t,hr,mw,yi,rr,rr_t) {

Domain **domain_reactant = hr->domain_reactant;

real *stoich_reactant = hr->stoich_reactant;

int *reactant = hr->reactant;

int i;

int sp_id;

int dindex;

Thread *t_reactant;

real ci;

real T = 1200.; /* should obtain from cell */

/* instead of compute rr directly, compute log(rr) and then

take exp */

*rr = 0;

for (i=0; i < hr->n_reactants; i++)

{

sp_id = reactant[i]; /* species ID to access mw and yi */

if (sp_id == -1) sp_id = 0; /* if phase does not have species,

mw, etc. will be stored at index 0 */

dindex = DOMAIN_INDEX(domain_reactant[i]);

/* domain index to access mw & yi */

t_reactant = THREAD_SUB_THREAD(t,dindex);

/* get conc. */

ci = yi[dindex][sp_id]*C_R(c,t_reactant)/mw[dindex][sp_id];

ci = MAX(ci,SMALL_S);

*rr += stoich_reactant[i]*log(ci);

}

*rr += log(Arrhenius + SMALL_S) -

E_Activation/(UNIVERSAL_GAS_CONSTANT*T);

/* 1.e-40 < rr < 1.e40 */

*rr = MAX(*rr,-40);

*rr = MIN(*rr,40);

*rr = exp(*rr); }

Rick:

You were right, I made some changes to the rate and it shows some improvements. Thanks!

Hussein:

Well at this point I am really busy with my project and cannot really go into details to debug your code, and I am not also completely familiar with your model. I need to submit this work by the end of this month and it is a really time taking project simulating such process. If you still have time, please wait until I get some free time.

Thanks Hossein, much appreciated your time and good luck with your project. I will comeback to you if I'm not able to solve the problem. Thanks again

Hi Hossein, I have been able to solve the problem and the UDF is complied successfully and it shown in the interaction tab. But now divergence detected in AMG solver. When I disable the reaction the solution converge without any error. DO you have any thoughts?

do you hook your compiled UDF to your "reaction" tab under phase interaction?

Yes this is what I did and the error I receive is:

Error: Divergence detected in AMG solver: vof-1