Study of Heat Transfer from a Sphere Body to Flowing Media

Abstract

In the present research the convective heat transfer from a hollow copper sphere(10.2 cm in diameter) to air is studied at different temperatures of sphere surface.The experiments were carried-out in an experimental channel (245 x 48 x 50 cm)and the velocity of air was changed by varying the orientation of the gate of thechannel which has four levels. A fan of moderate capacity generates air into thechannel.The sphere was heated by hot water at approximately constant wall at differentmeasured temperatures 40, 50, 60, 70 and 80 0C and local heat transfer coefficientswere calculated. This process was done by placing ten thermocouples into the innersurface of sphere. These thermocouples were connected to a digital reader whichgives the instantaneous temperature of a specified region. The thermocouples werenumbered and distributed in an equal angular displacement of 36 degrees.The determination of heat transfer coefficient was done through two regions, thefirst called the front region, which faces the fan, and the second called the wake orbackward region in which vortices were generated and built-up. A variance oftemperature was recognized between these two regions in such a way that frontheat transfer coefficient was higher than that for backward region.The analysis of the present work is based on Reynolds number which is changefrom 12894 to 33282 depends on the velocity of the used fan. The experimentalresults of this study were compared with Kendoush analytical correlation (1995)together with a number of certain other mathematical equations obtained from theliterature. It was found that this comparison was good especially at highertemperatures.