| Popis: |
Two-phase flow in pipes occurs frequently in petroleum refineries. Simulation and design calculations for their processing units require methods for predicting void fractions and axial pressure drops, thus making it essential that precise models of the relevant thermo-fluid dynamics be combined with efficient numerical techniques. In this work, the two-phase flow with phase change problem of a refinery multicomponent naphtha (C5-C8) was modeled through the steady-state one-dimensional mixture model, which comprises continuity, momentum and energy differential equations for the mixture, in addition to an extra continuity equation for the vapor phase. Relative motions between the phases are accounted for by a constitutive expression for the one-dimensional drift velocity. Evaporation and condensation are considered via vapor-liquid equilibrium calculations, and suitable thermodynamic methods are also applied in the evaluation of physical properties. It is proposed in this work that this rigorous formulation fits in the scope of Differential-Algebraic Equations (DAE) systems and is preferably solved by proper established numerical methods rather than the customary iterative segregated semi-implicit algorithms based on finite volume approaches. Efficiency and accuracy gains are demonstrated as a result of the proposed numerical strategy, which yields higher-order numerical solutions in much less CPU time. Specific regularization functions were also developed in order to eliminate expected numerical issues of convergence failure due to discontinuities in the drift-flux parameters at flow-regime transitions. |
