STP1534

    A Volume of Fluid Phase Change Model on Adaptive Octree Grids

    Published: Feb 2012


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    Abstract

    A three-dimensional phase change model using finite volume has been developed. Interface thermal conditions that are consistent with the mixture formulation within the volume tracking framework are introduced. The computational grid is dynamically adapted near the interface using an octree based structure. Up to three levels of adaption are used to provide improved accuracy in regions of steep gradients of flow variables near the liquid-vapor interface at a reduced computational cost. Interface jump conditions are imposed by specifying mass, momentum, and energy sources for the mixture variables in the interface cells. Second order accurate liquid and vapor temperature gradients at cell faces are calculated based on the location and orientation of the interface (sharp interface approach). These estimates are then used to calculate the mass source terms, which are distributed in the interface cells consistent with the mixture formulation. Such an approach maintains the interface at saturation while the mixture temperatures of the liquid and vapor in the interface cells can be superheated. A one-dimensional cavity flow problem is used to test for the proper coupling of vapor generation rate with energy and momentum flux effects. Three-dimensional bubble growth rates at 5°C uniform superheat (Ja = 8.6, density ratio ~140, and conductivity ratio ~2.3) of refrigerant FC-87 are compared with theory in the diffusion controlled regime. The analytical solution of Mikic et al. for bubble radius as a function of time with a non-zero initial radius is used to validate the numerical solution. The numerical solution is validated against theoretical prediction of bubble radius as a function of time for a more complete validation of the balances of mass, momentum, and energy at the liquid-vapor interface.

    Keywords:

    phase change, boiling flows, diffuse interface models, volume of fluid, octree grids, adaptive mesh refinement, bubble growth rates


    Author Information:

    Akhtar, Mohammad W.
    Dept. of Mechanical Engineering, Univ. of Houston, Houston, TX

    Kleis, Stanley J.
    Dept. of Mechanical Engineering, Univ. of Houston, Houston, TX


    Paper ID: STP153420120001

    Committee/Subcommittee: D02.01

    DOI: 10.1520/STP153420120001


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