EXPERIMENTAL STUDY OF NATURAL CONVECTIVE HEAT TRANSFER FROM AN INCLINED ISOTHERMAL SQUARE CYLINDER WITH AN EXPOSED TOP SURFACE MOUNTED ON A FLAT ADIABATIC BASE

摘要

Natural convective heat transfer rates from inclined cylinders with a square cross-section and which has an exposed top surface have been experimentally studied. When relatively small square cylinders with exposed top surfaces inclined at an9* angle to the vertical are used, the inclination angle to the vertical has, in general, a considerable effect on the magnitude of the mean heat transfer rate and on the nature of the flow over the surfaces that make up the cylinder. In the situation here considered the cylinder is mounted on a large flat essentially adiabatic surface with the other cylinder surfaces exposed to the surrounding air and with the cylinder, in general, inclined to the vertical at angles between vertically upwards and vertically downwards. The situation considered is an approximate model of that which occurs in some electrical and electronic component cooling problems. The cross-sectional size-to-height ratio of the square cylinders used in the present study was comparatively small, i.e. the square cylinders were short, the width, w, of the square cylinders being 25.4 mm and the width-to-height ratios of between 1 and 0.25 being used. One of the main aims of the present work was to determine how the cross-sectional size-to-height ratio of the square cylinder, i.e., w/h, influences the mean heat transfer rate from the cylinder at various angles of inclination between vertically upwards and vertically downwards. The heat transfer rates were determined by the transient method, this basically involving heating the model and then measuring its temperature-time variation while it cooled, the tests being carried out inside a large enclosure. Tests were carried out in air with all models at various angles of inclination to the vertical between vertically upwards and vertically downwards. The effects of w/h, Rayleigh number, Ra, and angle of inclination, Φ, on the mean Nusselt number, Nu for the entire cylinder have thus been studied. The Rayleigh number, Ra, based on the cylinder height, h, was betweenapproximately 1E4 and 5E6. The experimental results have been compared with the results obtained in an earlier numerical study.