Hello everyone.
I have a question regarding heterogeneous chemical kinetics in MFix-DEM: is it possible to define gas-solid reactions of the form A(s)+B(g) → C(s)+D(g), i.e. the reaction of a solid species A and a gaseous species B that turn into a solid species C and a gaseous species D?
I saw an equation in Table 2 of this article involving Xn. Is this the mass fraction of species n in the particle and is this equation solved for every particle?
Many thanks for your answer.
Regards.
Answering your questions in reverse order:
Xn is mass fraction and to the best of my knowledge this is solved for each particle - as particles in different parts of the domain will be exposed to different reactants.
The limits on what types of reactions are permissible are a bit complex. The MFiX GUI will try to guide you and not allow you to define unpermitted reactions. However sometimes you can still set something up that will be rejected by the solver when you run the simulation. My advice is just to try it and see what happens. Here’s the exact rules:
Heterogeneous reactions referencing three or more phases:
Either only one phase has a net mass loss or one phase
has a net mass gain. Specifically, two or more phases cannot
have a net mass loss while two or more phases have a net mass
gain.
The following examples illustrate valid and invalid reactions. For
these examples, FC1, FC2, and sSoot, represent solid carbon in
solids phases 1, 2 and 3, respectively. All other species belong
to the gas.
Example 1: VALID
Example 2: VALID
Example 3: VALID
Example 4: INVALID
The heat of reaction, DH, and how it is distributed between phases,
fracDH, must be specified if there are two or more solids phases
listed as either reactants or products.
Example 5: DH and fracDH NOT REQUIRED
Example 6: DH and fracDH REQUIRED
Example 6: DH and fracDH REQUIRED
Hello, thank you very much for your answer!
In MFix-DEM, is it possible to simulate the following reaction?
Species A remains species A until a nucleus of species B appears on its surface, whereupon the entire particle is instantaneously converted into species B.
The appearance of the nucleus is a probabilistic process and the nucleation time tau is exponentially distributed.
Is it possible to access the time step dt of the numerical solver of MFix-DEM?
I would like to define the reaction rate as follows:
generate a potential nucleation time tau via random numbers
if tau < dt, the nucleus appears and species A is instantaneously transformed into species B. I would set a very large value for the reaction rate.
if tau > dt, nothing happens and rate = 0.
However, in order for that solution to work, I must be able to use the numerical time step of Mfix-DEM in my definition of the heterogeneous reaction rate.
Is this possible?
I thank you very much ahead of time for your answer!