<strong>in</strong> the Cahn-Hilliard model than <strong>in</strong> the van der Waals model, it is nevertheless a real difficulty toensure that these modifications do not <strong>in</strong>volve modifications on the mesoscopic characteristics ofthe flow.This analysis shows that the adaptation of physical diffuse <strong><strong>in</strong>terface</strong> <strong>models</strong> to mesoscopicproblems is rather difficult and tricky. We showed <strong>in</strong> particular that it is important to know thesharp <strong><strong>in</strong>terface</strong> model that the diffuse <strong><strong>in</strong>terface</strong> model must mimic. It is <strong>in</strong>deed a reference thathelps to develop the “equivalent” diffuse <strong><strong>in</strong>terface</strong> model. Moreover, we showed that the difficultycomes from the fact that we use only physical variables (mass density ρ or mass fractionc) and that these physical variables are important to characterize (i) the <strong><strong>in</strong>terface</strong> structure (thatis aimed at be<strong>in</strong>g modified) and (ii) bulk phases properties (pressure, chemical potential, etc).We showed that modify<strong>in</strong>g one feature without modify<strong>in</strong>g the other is difficult and tricky. Thesystem lacks degrees of freedom. This degree of freedom can come from the <strong>in</strong>troduction of anotherparameter whose ma<strong>in</strong> goal would be to characterize only the <strong><strong>in</strong>terface</strong> structure and notthe bulk properties. The phase-field variable ϕ often used <strong>in</strong> other applications of diffuse <strong><strong>in</strong>terface</strong><strong>models</strong> can be <strong>in</strong>terpreted as such a variable. It has recently been shown [Jamet and Ruyer,2004] that such a phase-field model<strong>in</strong>g is possible for liquid-vapor flows. The <strong>in</strong>troduction of thephase-field <strong>in</strong>deed allows to easily decouple the <strong><strong>in</strong>terface</strong> properties from the bulk properties.ReferencesJ. U. Brackbill, D. B. Kothe, and C. Zemach. A cont<strong>in</strong>uum method for model<strong>in</strong>g surface tension.J. Comp. Phys., 100:335–354, 1992.J. W. Cahn and J. E. Hilliard. Free energy of a nonuniform system. I. <strong>in</strong>terfacial free energy. J.Chem. Physics, 28(2):258–267, 1958.J. W. Cahn and J. E. Hilliard. Free energy of a nonuniform system. II. thermodynamic basis. J.Chem. Physics, 30(5):1121–1124, 1959a.J. W. Cahn and J. E. Hilliard. Free energy of a nonuniform system. III. nucleation <strong>in</strong> a twocomponent<strong>in</strong>compressible <strong>fluid</strong>. J. Chem. Physics, 31(3):688–699, 1959b.J.-M. Delhaye, M. Giot, and M. L. Riethmuller. Thermohydraulics of two-phase systems for <strong>in</strong>dustrialdesign and nuclear eng<strong>in</strong>eer<strong>in</strong>g. Hemisphere Publish<strong>in</strong>g Corporation, 1981.F. Dell’Isola, H. Gou<strong>in</strong>, and G. Rotoli. Nucleation of spherical shell-like <strong><strong>in</strong>terface</strong>s by secondgradient theory: Numerical simulations. Eur. J. Mech. B/Fluids, 15(4):545–568, 1996.J. E. Dunn and J. Serr<strong>in</strong>. On the thermodynamics of <strong>in</strong>tersticial work<strong>in</strong>g. Arch. Rational Mech.Anal., 88:88–133, 1965.C. Fouillet. Généralisation à des mélanges b<strong>in</strong>aires de la méthode du second gradient et application à lasimulation numérique directe de l’ébullition nucléée. Thèse de doctorat, Université Paris VI, 2003.C. Fouillet, D. Jamet, and D. Lhuillier. A cont<strong>in</strong>uous <strong><strong>in</strong>terface</strong> model for the direct numerical simulationof phase-change <strong>in</strong> two-component liquid-vapor flows. In 2002 Jo<strong>in</strong>t ASME/EuropeanFluid Eng<strong>in</strong>eer<strong>in</strong>g Division Summer Conference, Montreal, Canada, July 14-18, 2002.G. P. Galdi, D. D. Joseph, L. Preziosi, and S. Rionero. Mathematical problems for miscible andcompressible <strong>fluid</strong>s with korteweg stresses. European Journal of Mechanics B Fluids, 10(3):253–267, 1991.H. Gou<strong>in</strong>. Energy of <strong>in</strong>teraction between solid surfaces and liquids. J. Phys. Chem. B, 102:1212–1218, 1998. doi: 10.1021/jp9723426.34
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