[ASimonsen]

Hi

I'm using DEFINE_SOURCE to define various source terms in my model. In order to increase stability, I'm linearizing the sources. The UDF-manual states the following (Page 127 in Fluent UDF manual for release 18.0):

"
Note that the source term derivatives may be used to linearize the source term if they enhance the stability of the solver. To illustrate this, note that the source term can be expressed, in general, as Equation 2.10 (p. 127), where Phi is the dependent variable, A is the explicit part of the source term, and B*Phi is the implicit part.
S_Phi = A + B * Phi
"

I'm specifying source terms for momentum, energy and mass. I've found the following information about the three terms:

Momentum:
- Dependent variable (Phi): Velocity [m/s]
- Unit of A and S_Phi: [N/m^3]
- Unit of B: [(N/m^3)/(m/s)]

Energy:
- Dependent variable (Phi): Temperature [K]
- Unit of A and S_Phi: [W/m^3]
- Unit of B: [(W/m^3)/(K)]

Mass:
- Dependent variable (Phi): ???
- Unit of A and S_Phi: [kg/(s*m^3)]
- Unit of B: [(kg/(s*m^3))/(???)]

As you can see, I don't know what the dependent variable is for mass sources. Can anyone help me with that?

Regards Anders