Effects of vortical structures in a multi-phase flow on the thermal and mass transfer

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In 1999 and 2000, we spent research time for creating experimental apparatus and making new simulation codes. Head investigator coded a very accurate Fortran code to simulate flows within a closed domain. He carefully arranged the mesh points for high resolution simulation and obtained optimal mesh arrangement. It is also necessary to arrange velocity, pressure and temperature fields in a staggered way to prevent artificial numerical instability to occur. Another investigator constructed a long duct with a square cross section to measure turbulent flow with very small air bubbles. He injected air bubbles by oscillating one side wall and measured velocity field by LDV. In 2001, the head investigator examined a natural convection in a cube by visualizing AVS. It is found that the flow pattern changes as time proceeds and finally attains one vortex flow. It is also studied on the appropriateness of numerical calculation by conservative or non-conservative form for the nonlinear terms. In the final year, 2002, the head investigator studied diffusion of small particles in a natural convection in a cube over the Rayleigh number from 5000 up to 12000. He found an existence of the stream line chaos as found in a cavity flow before. It is found that there exist two tori and two fixed lines within them. It is very interesting that though in stream line chaos of the cavity flow, the structure of chaos varies largely as the Reynolds number increases, in the case of the natural convection, the structure of chaos varies little as the Rayleigh number increases.