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T. Laurila1, M. Saukkonen1, J. Ruokolainen2, T. Ala-Nissila1 1 Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FI-02015 HUT, Finland. 2 CSC - Finnish IT Center for Science, P.O. Box 405,FI-02101 Espoo, Finland We study the dynamics of fluid systems composed of two phases of a sigle component, such as a mixture of water and water vapour. Diffuse interface methods [1] can be used to desribe the system in a thermodynamically consistent manner [2] without explicitly keeping track of interfaces. An implementation of standard fluid dynamics on a FEM platform (ELMER) is converted to the diffuse interface method. Using the Van der Waals equation of state and proper boundary conditions, we obtain a consistent description of a liquid/gas system in coexistence (closed system) or undergoing a transition (open system). However, we find that this description requires the use of interface widths in the range of those of real systems. This leads to a dead-end with numerics, since it is numerically unfeasible to solve a system large enough to contain a supercritical domain. Our proposed solution inlvolves fitting the two-phase bulk free energy to obtain the stable state densities and the surface tension according to experimental or approximated values. This allows us to loosen the physical requirement on the interface width, while still maintaining a connection with the corresponding sharp interface picture. Furthermore, an addition to the boundary condition is needed to account for three-phase contact line motion. We aim to apply the resulting model to two-phase phenomena in microfluidics [3], and boiling in particular [4]. References [1] D. M. Anderson, C. B. McFadden, A. A. Wheeler, Ann. Rev. Fluid Mech. 30, 139 (1998). [2] P. Espa%G˜%@nol, J. Chem. Phys. 115, 5392 (2001). [3] E. Zwaan et al. Phys. Rev. Letters 98, 254501 (2007). [4] V.S. Nikolayev et al., Phys. Rev. Letters 97, 184503 (2006). |
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