Two-fluid model with physics-based inertial coupling for boiling flows

The two-fluid model (TFM) has become the basis of numerical codes for engineering analysis of two-phase flows in most of the energy systems where boiling is present. However, the completeness of the model is still disputed because, in its usual form, the momentum conservation equations are elliptic, which, among other things, causes the solutions of short wavelength perturbations to have infinite growth rate. Recently, it has been shown that well-posed instances of the TFM can be derived using the variational principles. This paper presents a complete formulation of the TFM for boiling flows that renders the equations hyperbolic by incorporating physics-based inertial coupling between phases. The equations are cast into two canonical motion modes, namely, the center-of-mass flow and the relative motion between the fluids, which have different temporal and spatial scales, and so are easier to analyze independently. The influence of the inertial coupling parameters is analyzed in a case study of boiling channel oscillations.