[anubhavd]

I am trying to write a ufd code for nucleation of zinc vapor. As a result of nucleation the concentration of zinc vapor decrease. Can anybody help me from where i should start ? Should I treat this(nucleation) as mass sink term? If yes then how should I add this sink term in my model.

My model can be assumed a simple rectangle with one inlet and outlet.The zinc vapor are introduced from inlet at high temperature and as it proceeds to outlet there is drop in temperature. As a result of this temperature drop nucleation occurs.

[Bruno Machado]

so the nucleation has a dependence on temperature (does it depends on position)? Can you post the formula?

You need to add a source term in the specie you want to decrease and also the same term in the mass equation (continuity), otherwise your balance wont match.

[anubhavd]

The formula for nucleation rate (m^-3 S^-1) is
Nucleation rate = (4*pi*r^2)*(exp(-del G/KT))

In short it depends upon temperature and mass concentration of zinc vapor rest all are constant.

[Bruno Machado]

Originally Posted by anubhavd

The formula for nucleation rate (m^-3 S^-1) is
Nucleation rate = (4*pi*r^2)*(exp(-del G/KT))

In short it depends upon temperature and mass concentration of zinc vapor rest all are constant.

Fluent source terms are defined in a generation rate/volume. In case of mass, for example, its unity is kg/m3.s. Thus, you gotta check your equation to match the same unity. This is just a draft of your source term. You need to define r, K and if -del G is the gradient of a concentration, you need to create an UDS and define it as your specie in order to obtain the gradient.

#include "udf.h"

#define PI 3.14159265

DEFINE_SOURCE(nucleation_source,c,t,dS,eqn)
{
real T, K, r;

T = C_T(c,t);
r = .......................;
K = ......................;

source = (4.0*PI*pow(r,2.0))*(exp(-del G/K*T));
dS[eqn] = 0.0;

return source;
}

[anubhavd]

Dear Bruma

In Ansys help it is written that:
Note that if you define a mass source for a cell zone, you should also define a momentum source and, if appropriate for your model, energy and turbulence sources.
If you define only a mass source, that mass enters the domain with no momentum or thermal heat. The mass will therefore have to be accelerated and heated by the flow and, consequently, there may be a drop in velocity or temperature. This drop may or may not be perceptible, depending on the size of the source. (Note that defining only a momentum, energy, or turbulence source is acceptable.)

Is it necessary in mine case also?

[Bruno Machado]

Originally Posted by anubhavd

Dear Bruma

In Ansys help it is written that:
Note that if you define a mass source for a cell zone, you should also define a momentum source and, if appropriate for your model, energy and turbulence sources.
If you define only a mass source, that mass enters the domain with no momentum or thermal heat. The mass will therefore have to be accelerated and heated by the flow and, consequently, there may be a drop in velocity or temperature. This drop may or may not be perceptible, depending on the size of the source. (Note that defining only a momentum, energy, or turbulence source is acceptable.)

Is it necessary in mine case also?

I cant tell you. you should do this analyse and check if it is significant or not.