[abgoel363]

I want to understand the mathematics behind the UDF given below, how it is calculating the reaction rate. Specifically, the loop running to calculate ci and prod. what this loop is calculating and why?

Thank you so much for the help in advance.


#include "udf.h"

DEFINE_VR_RATE(vol_reac_rate,c,t,r,wk,yk,rate,rr_t )
{
real ci, prod;
int i;

/* Calculate Arrhenius reaction rate */

prod = 1.;

for(i = 0; i < r->n_reactants; i++)
{
ci = C_R(c,t) * yk[r->reactant[i]] / wk[r->reactant[i]];
prod *= pow(ci, r->exp_reactant[i]);
}
*rate = r->A * exp( - r->E / (UNIVERSAL_GAS_CONSTANT * C_T(c,t))) *
pow(C_T(c,t), r->b) * prod;

*rr_t = *rate;

/* No "return..;" value. */
}

[pakk]

What it is calculating: the code has a comment

* Calculate Arrhenius reaction rate *

So, that is probably what it is calculating. It is a loop because every reactant has a different rate.

Why, you also asked. I don't know how to answer it it in a different way than: because the person who wrote this code, needed the result of the calculation.

[abgoel363]

Thanks for the reply.

By "what it is calculating", I mean the reason to calculate ci and prod, as Arrhenius equation is defined as
k = A* exp(-E/RT) * T^b

Please explain the meaning and purpose of calculating prod.

Also, what does wk[r->reactant[i] signifies?
Is yk[r->reactant[i] means initial mass fraction of reactants and
r->exp_reactant[i] means rate exponent of the reactants??

[pakk]

Originally Posted by abgoel363

Thanks for the reply.

By "what it is calculating", I mean the reason to calculate ci and prod, as Arrhenius equation is defined as
k = A* exp(-E/RT) * T^b

Please explain the meaning and purpose of calculating prod.

Also, what does wk[r->reactant[i] signifies?
Is yk[r->reactant[i] means initial mass fraction of reactants and
r->exp_reactant[i] means rate exponent of the reactants??

I guess prod is the product of the concentrations, used in the usual reaction rate equations.

But why this UDF? Is it from the manual? Where did you find it?

[abgoel363]

Yes, this is the example udf given in the manual for volumetric reaction rate. I have made the changes in it as per my requirement in this code but not able to understand the mathematics of this code by calculating ci and prod. The rest is quite understandable though.

[pakk]

Then look in the manual. Wk and yk are the fifth and sixth argument of the macro.

Above the example, the arguments are explained. The fifth and sixth are mw and yi. So read what they mean.