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[FAQ]

Sometimes it is required to specify the multiple species as the evaporating species in DPM. This is one of the requirements for volatile break-up while modeling coal combustion or gasification. However, in FLUENT only one species is allowed as the evaporating species. Above limitation can be worked around using a pseudo species and a pseudo reaction. Define a pseudo species (e.g. volatile) in the mixture. Specify this species as the evaporating species. Then, define a pseudo reaction (e.g. volatile-break-up-reaction). Reactant of this reaction is the pseudo species and the products would be the required multiple species of the volatile break-up. This reaction should be faster than other reactions included in the model so that species evolved due to volatile break-up are not limiting the other reactions. This can be done by specifying large pre-exponential factor for Laminar finite rate model or large mixing rate constant, A for the eddy dissipation model. Molecular weight and standard state enthalpy for the pseudo species can be adjusted so that no heat is produced or consumed in the volatile break-up reaction.