In this study, natural convective heat transfer from cylindrical slender rods with different length and diameters and different angles of inclination (from horizontal to vertical) at constant heat flux condition was measured. For each inclination angle, average natural heat transfer coefficient was obtained. The effects of the angle of inclination and that of the diameter and length of cylinders on heat transfer rates were examined. The angles of 0°, 15°, 30°, 45°, 60°, 75° and 90° were studied. Experimental results show that increasing the diameter of the cylinder, with constant length and the Rayleigh number based on length causes the decrease of the Nusselt number. Increasing the length of the cylinders, with constant diameter and Rayleigh number based on diameter causes the decrease of the Nusselt number. Increasing either the angle of inclination or length decreases the effect of diameter on the heat transfer rate. Experimental results in terms of Nusselt number were correlated as a function of modified Rayleigh number and dimensionless parameters containing diameter, length and orientation angle.

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