UBC Theses and Dissertations

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UBC Theses and Dissertations

Free convective heat transfer from a heated horizontal downward facing surface Wu, Erh-Rong


A study of laminar free convection about horizontal plates of finite width with one side heated isothermally and the other insulated is presented in this thesis. This investigation forms part of a continuing program, and its technological origin and significance are discussed in the introduction. The governing partial differential equations comprising the continuity, momentum and energy equations are solved numerically through a finite difference method using a successive-over relaxation technique for a Rayleigh number range from 0.22 to 500, at three values of Prandtl number (0.72, 5.0 and 10.0). The variation of the flow, vorticity and temperature fields with the change of both Grashof and Prandtl numbers is discussed on the basis of the streamline, iso-vorticity and isothermal plots obtained . The effect of Prandtl number alone on the momentum field, energy distribution and heat transfer rate is discussed, by a comparison of the isotherms, streamlines and correlation curves obtained for the three different Prandtl numbers. The theoretical analysis places emphasis on the singular nature of the boundary conditions specified and on the influence of the finite size of the domain of the finite difference scheme. Some results for an upward facing horizontal isothermally heated plate of finite width were also obtained, and were compared to data for the downward facing case. A semi-focussing Schlieren colour system was used order to investigate experimentally the flow behaviour on a horizontal plate with the heated surface facing-downward The experimental results sought were evidence of the non-boundary layer nature of the flow. The evidence of non-boundary layer flow was obtained conclusively.

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