[ankiit_c11]

I am relatively new to UDFs and I have been working on a project where I need to define a UDF for a heterogenous reaction I have in my simulation.

I have been reading about DEFINE_HET_RXN_RATE (name,c,t,r,mw,yi,rr,rr_t) from the Ansys UDF manual but I got confused at the point where the documentation referred to some indexes to extract the molecular weight and mass fraction of species.

Here is what the documentation says:

mw[i][j] will give molecular weight of species with ID j in phase with index i. For phasewhich has fluid material, the molecular weight can be accessed as mw[i][0].

yi[i][j] will give mass fraction of species with ID j in phase with index i. For phase which has fluid material, yi[i][0] will be 1.

I am not able to understand what would be right index and id for the species I want to refer to.

I have 4 items in materials > fluid. In my udf, how do I get the molecular weight and mass-fraction of each species.

If any clarification is needed please ask. I am not very familiar with the technicalities and am badly stuck at this point. Any help is appreciated.