In the mixture Eulerian two-phase model, the two-phase mixture is modeled as a homogeneous mixture in each computational cell. All the liquid and gas species are assumed to be perfectly mixed locally, and there is no attempt to define an interface between the two phases in the cell. The concentration of each species, which is either a liquid species or a gas species, is tracked by its mass fraction, . The species transport equation can take the form of Equation 2–1, without considering the source terms for combustion and sprays. The equation is re-written as follows:

(11–7)

In which is density of the two-phase mixture, subscript is the species index looping over all the gas and liquid species, is the total number of liquid and gas species, is the flow velocity vector, and is the mass fraction of species .

Due to the assumption that the two phases have equal velocities, temperatures, and pressures in each computational cell, the momentum equations Equation 2–3, Equation 2–4 and the energy equations Equation 2–5, Equation 2–6 can be applied in the Mixture Eulerian Two-Phase model, provided that the viscosity () and thermal conductivity () are properly defined for the two-phase mixture.

The Eulerian two-phase flow simulation can be used without considering phase-change or gas-cavitation effects. In this case, the concentrations of each species, , are affected only by initial conditions and flow transport. If phase change and/or gas cavitation are considered, they are modeled as local processes, in which mass is transferred locally between the gas and liquid phases or between the free gas and dissolved gas while the total mass of each chemical species is conserved. Consequently, the concentrations of each species are affected not only by initial conditions and flow transport, but also by the local mass transfer processes. Modeling Phase Change describes phase change models and Modeling Gas Cavitation describes a gas cavitation model in more detail.