[Laexzzz]

I want to use UDS for my simulation.

My reaction

A => B

So, i want to compare results of Fluent reaction module and results of UDS transport equation.

UDS depends of concentration A.

Source equation is S = Kd*[A] (k - is a reaction rate constant and [A] is a molar concentration)

Finally, the concentration of reactant B and UDP should be identical but it is not the case

My code

#include "udf.h"
#define kd0 1.58e+15

DEFINE_SOURCE(UDS0_source,c,t,dS,eqn)
{
real UDS0_source;
real temp = C_T(c,t);
real Dens = C_R(c,t);
real kd = kd0*exp(-15500/temp);
real IniMC1;
real UDSMC_source;

AMC = (C_YI(c,t,0)*Dens) / 164;
UDSMC_source = kd*AMC;
UDS0_source = UDSMC_source*164;
dS[eqn] = 0;
return UDS0_source;
}

May be somebody have any example with reaction and UDS? Or somebody can give any advice in that domain?

Alexey

[billwangard]

Hi,

You will need one sink and one source.

The sink is for A and the source is for B.

if your reaction is

rA = - k * [A],

additionally, rB = -rA, and the net mass source has to be zero.

and [A] = D * Y(0), where D is a constant (dens/164).

Thus, rA = -k * D * Y(0)
and

d(rA)/dY = dS[eqn] = -k * D

In your UDF, the Jacobian was 0... This is incorrect.

Also rB = -rA, and d(rB)/dY(0) = k * D.

Thus, you should have two DEFINE_SOURCE routines, one for each of your scalars. There should be no MASS SOURCE, since mass is not destroyed in the conversion of single molecule A to single molecule B.

Good Luck,
Bill

[Laexzzz]

Originally Posted by billwangard

Hi,

You will need one sink and one source.

The sink is for A and the source is for B.

if your reaction is

rA = - k * [A],

additionally, rB = -rA, and the net mass source has to be zero.

and [A] = D * Y(0), where D is a constant (dens/164).

Thus, rA = -k * D * Y(0)
and

d(rA)/dY = dS[eqn] = -k * D

In your UDF, the Jacobian was 0... This is incorrect.

Also rB = -rA, and d(rB)/dY(0) = k * D.

Thus, you should have two DEFINE_SOURCE routines, one for each of your scalars. There should be no MASS SOURCE, since mass is not destroyed in the conversion of single molecule A to single molecule B.

Good Luck,
Bill

Thank you for your response!
Then another question.

Scalar must move with the flow.
Now I try to explain what I want to do. I want to create scalar. Its source term depend on the concentration of the material component of the mixture. Scalar moves with the flow.

So I should set flow function of scalar "mass flow rate"? But flow rate of scalar is 0 at time = 0. Transient and dif members of transport equation should be 0?

[Laexzzz]

Guys, some ideas? I'm seriously stuck at this moment