The Coupled Species model is an extension of the Coupled Flow model. Together with the Coupled Energy model, it solves the conservation equations for mass, momentum, and energy of a multi-component fluid mixture simultaneously using a time- (or pseudo-time-) marching approach. For a mixture of N components the Coupled Species model introduces N-1 transport equations into the system. Together with global mass continuity, these equations provide a means for updating the field of N mass fractions defining the mixture composition. Inter-equation coupling is fully maintained between all equations in the system, including species transport with respect to momentum and energy, and vice versa.
For isothermal simulations of multi-component fluid mixtures it is possible to omit the Coupled Energy model, in which case the Coupled Species model, together with the Coupled Flow model, will solve the conservation equations for mass and momentum simultaneously.