| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 90 === An analysis is conducted to study the two dimensional laminar film condensation heat transfer with the effects of applied magnetic field or downward flowing vapors onto a horizontal wavy plate or disk. In the presence of magnetic field, the electrically conducting film will be governed by the elemental force-Lorentz force. The classical condensation model of Nusselt-Rohsenow’s analysis combined with the set of magnetohydrodynamic equations is utilized to treat the liquid film layer. Another case for the free and forced convection film condensation with pure saturated vapor, the Shekriladze and Gomelauri’s shear stress model is adopted appropriately for the liquid-vapor interfacial condition. Both cases are investigated with some general assumptions like liquid inertia and energy convection terms neglected.
An essential part of the present analysis is that the boundary condition at the plate edge is established by the application of Minimum mechanical energy principle from the open channel flow theory. To obtain the critical condensate layer thickness, the mass and energy equations must satisfy the conservation balance at the interface. An adequate implicit cubic spline scheme is employed for the numerical solution of the governing equations.To sum up the physical phenomena, results of the complete model were discussed in dimensionless form, including several presented parameters like Hartmann number, Rayleigh number, Jacob number and Reynolds number.
According to the numerical results, the flow momentum will be retarded, but the stability and the heat transfer distribution will be increased and normalized due to the externally applied magnetic field. For film condensation of downward flowing vapor, it is found that as the vapor velocity is increasing, the mean heat transfer coefficient is changing from the free convection region into the forced convection region through a transition zone. As for the influence of wavy surface effect on the mean heat transfer coefficient, the results shows that if the total waviness number is odd, the heat transfer characteristics will be proportional to the waviness amplitude.
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