This work takes place in steam generator flow studies, and we consider here steady-state three-dimensional two-phase (liquid and gas) flows. The main goal is to improve the modeling of kinetic imbalance between the phases. We present a method that solves the mixture (liquid-gas) mass and enthalpy equations, and two momentum equations: one for the mixture and one for the gas. This choice is equivalent to solving the gas and the liquid momentum equations, but it is better suited to the Chorin projection method used for the pressure calculation. Solving two momentum equations instead of solving only the one for the mixture introduces the use of correlations for the gas-liquid friction but avoids the use of a correlation for the drift velocity and opens the way to a finer analysis of the relative dynamic behavior of each phase.