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      Thermodynamically consistent modeling and simulation of multi-component two-phase flow model with partial miscibility

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          Abstract

          A general diffuse interface model with a realistic equation of state (e.g. Peng-Robinson equation of state) is proposed to describe the multi-component two-phase fluid flow based on the principles of the NVT-based framework which is a latest alternative over the NPT-based framework to model the realistic fluids. The proposed model uses the Helmholtz free energy rather than Gibbs free energy in the NPT-based framework. Different from the classical routines, we combine the first law of thermodynamics and related thermodynamical relations to derive the entropy balance equation, and then we derive a transport equation of the Helmholtz free energy density. Furthermore, by using the second law of thermodynamics, we derive a set of unified equations for both interfaces and bulk phases that can describe the partial miscibility of two fluids. A relation between the pressure gradient and chemical potential gradients is established, and this relation leads to a new formulation of the momentum balance equation, which demonstrates that chemical potential gradients become the primary driving force of fluid motion. Moreover, we prove that the proposed model satisfies the total (free) energy dissipation with time. For numerical simulation of the proposed model, the key difficulties result from the strong nonlinearity of Helmholtz free energy density and tight coupling relations between molar densities and velocity. To resolve these problems, we propose a novel convex-concave splitting of Helmholtz free energy density and deal well with the coupling relations between molar densities and velocity through very careful physical observations with a mathematical rigor. We prove that the proposed numerical scheme can preserve the discrete (free) energy dissipation. Numerical tests are carried out to verify the effectiveness of the proposed method.

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          Most cited references 21

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          A New Two-Constant Equation of State

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            Mixed Finite Elements for Elliptic Problems with Tensor Coefficients as Cell-Centered Finite Differences

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              Decoupled, Energy Stable Schemes for Phase-Field Models of Two-Phase Incompressible Flows

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                Author and article information

                Journal
                2016-11-25
                Article
                1611.08622

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                Custom metadata
                math.NA physics.comp-ph physics.flu-dyn

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