NATURAL CONVECTION IN A CYLINDRICAL SECTION WITH A STATIC PROTRUSION: NUMERICAL SIMULATION RELEVANT TO SUBCOOLED FILM BOILING

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Abstract
The aim of the present investigation was to study the convective processes on a protrusion with possible application to subcooled film boiling. Laminar Rayleigh Benard convection in a cylindrical section with a "bubble like" static protrusion was simulated numerically for a Prandtl number of unity. Intitially, Rayleigh Benard convection in a right circular cylinder was simulated to validate the numerical scheme. Predictions of variation of Nusselt number with Rayleigh number are made for 5 aspect ratios (ratio of the radius to the height of the cylinder) of (4, 2, 1, 0.5, and 0.25) and compared with experimental data available in the literature. By employing finite volume formulation the governing equations for conservation of mass, momentum and energy were discretized. Numerical grid generation and projection method were used to solve the set of conservation equations. Convective heat transfer rate as a function of protrusion height is calculated. Results show that the Rayleigh number has a stronger effect in enhancing heat transfer than the protrusion height. This can be interpreted as: the degree of sub-cooling has a stronger effect in enhancing the transport processes than the static height of the vapor bulge, in film boiling.

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