[mpieber]

Dear community members,

I am currently trying to implement the local chemical equilibrium approach in a reactive transient Fluent simulation, where each species is represented by a UDS. Target is that both species (UDS) transport equations and chemical equilibrium condition are fulfilled at the end of each time step, i.e. the species should be in local chemical equilibrium at any time.

Does anyone know a way (e.g. using UDFs) to implement local chemical equilibrium in a transient reactive Fluent simulation (when the species are represented by UDSs)?

Many thanks in advance for any help!

Best regards,

Markus

[vinerm]

How would you like to implement the equilibrium? In real systems, it is based on Gibbs Free energy. In simpler terms, you have to ensure that at certain conditions, which is defined by minimum Gibbs Free energy, mass transfer between two scalars settle down to be equal.

So, assuming that the said system of scalars has an equilibrium constant, which may or may not be a function of P and T (and the values of scalars themselves, which will make problem really non-linear), you should be able to define mass transfer based on the equilibrium constant.

[mpieber]

Dear Vinerm,

Thanks for your answer.

Assuming there is a functional relationship UDS2,eq = f(UDS1,eq) between UDS1 and UDS2 describing (chemical or adsorption) equilibrium, how could the mass transfer (source term) between UDS1 and UDS2 be defined (or how could the equilibrium condition be enforced otherwise)?

Best regards,
Markus

[vinerm]

You can use either DEFINE_MASS_TRANSFER or DEFINE_LINEARIZED_MASS_TRANSFER functions. Example for DEFINE_MASS_TRANSFER are available at

https://www.afs.enea.it/project/nept...udf/node63.htm