| Summary: | 碩士 === 中華大學 === 機械工程學系碩士班 === 101 === Two-dimensional natural heat transfer problems were studied in the work. Numerical validation with the previous results was performed. The flow structure and heat transfer enhancement were analyzed through a series of parametric constant. In the rhombic angle study of the cavity, the slant angle at 90o gives the highest heat transfer rate. The higher Rayleigh number, the more complex is the flow structure within the cavity. At slant angle at 15o or 165o, the smearing effect of the walls slows down the vortex motion within the cavity, and the structure of the flow becomes a single vortex. For the concentric cylinders
problem, the higher Rayleigh number the larger the mean Nusselt number. At the same time, the flow structure in the annulus diverse to more and more rolls and also more vortices within each roll. The phenomena explain the possible trail of the steady laminar
flow to unsteady turbulent flow. By putting the hot cylinder lower gives the buoyant jet
more space to travel and transfers more heat to the exterior for the eccentric cylinders
problem. Dual time stepping was used to solve the unsteady problem, the local iteration
numbers and physical time step can be used to control the temporal resolution of the results.
For the heat transfer of cylinder in the open space, the distance of the far field is examined
on the accurate of the local Nusselt number.
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