Laminar natural convection heat transfer about a heated horizontal cylinder having an attached or separated plume

Abstract

Laminar natural convection around two separate horizontal cylindrical configurations, the horizontal circular cylinder and the horizontal square cylinder, either with or without the outer enclosing circular cylinder, has been studied in this thesis. These flows, termed conveniently as the internal and the external natural convections, were investigated by many possible numerical and experimental means such as the finite difference method, the Galerkin finite element method, the fine-thermocouple temperature measurement, the smoke flow visualization and the Mach-Zehnder interferometry. Among the many interesting phenomena, substantial emphasis has been put on finding the correlation between the internal and the external natural convections, as well as on elucidating the separated plume above the horizontal upper surface of the square cylinder. Previously, it had been known in the literature that flow does not separate over a smooth heated curved surface. The argument needs now be corrected to include the separated natural convection for the case of the square cylinder sitting on its surface. When the square cyclinder was rotated 45$^\circ$ from this position, no separation was found despite the negative role of the sharp angled edges in the convective heat transfer. For the case of the horizontal circular cylinder placed inside of an another outer circular cylinder, parametric study on natural convection heat transfer was carried out in terms of the cylinder aspect ratio, eccentricity of the inner cylinder in both horizontal and vertical directions, azimuthal angularity of the inner cylinder and Rayleigh number. The conduction-dominant region in the annulus was mapped and the overall equivalent thermal conductivity was presented in a manner of emphasizing the relative degree of contribution between convection and conduction. For the case of the horizontal square cylinder with or without the outer enclosing circular cylinder, the temperature depression was observ...