Multicomponent Mass Transfer in the Compressible Flow of Semi-Continuous Mixtures Using Adaptive Characterization Method

Continuous mixtures are characterized by a large amount of components with similar properties which makes the determination of its exact composition unfeasible. These mixtures can be represented by a continuous component using a distribution function to characterize its composition. The distribution variable can be the molar mass or any other convenient property. Examples of continuous mixtures are oil fractions and polymer solutions. If the mixture has some known components, it is treated as a semi-continuous mixture. In order to solve the mass transport equation of a continuous component using the conventional discrete component approach, the distribution function has to be described by pseudo-components which are usually determined by quadrature based methods. However, the elevated number of pseudo-components required to capture the composition changes during mass transfer process still represents a drawback for CFD simulations. The present work developed the mathematical model and numerical solution of the multicomponent mass transport equations for the flow of semi-continuous mixtures. The model is an extension of the adaptive Quadrature Method of Moments (QMoM) for continuous thermodynamics to field problems. The method is called Direct QMoM for continuous thermodynamics. It was implemented in a CFD open-source package (OpenFOAM) as a compressible ideal gas flow solver. The DQMoM for continuous thermodynamics was compared with the conventional discrete component model (DCM) in a mixing flow of two mixtures consisting of 57 hydrocarbons and nitrogen. It was shown that 4 adaptive DQMoM pseudo-components were enough to reproduce the properties of the DCM mixture with a 2% accuracy. Furthermore, the DQMoM CFD solution was approximately two times faster than the DCM solution for the mixture flow.