Authors
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 the
channel which has four levels. A fan of moderate capacity generates air into the
channel.
The sphere was heated by hot water at approximately constant wall at different
measured temperatures 40, 50, 60, 70 and 80 0C and local heat transfer coefficients
were calculated. This process was done by placing ten thermocouples into the inner
surface of sphere. These thermocouples were connected to a digital reader which
gives the instantaneous temperature of a specified region. The thermocouples were
numbered and distributed in an equal angular displacement of 36 degrees.
The determination of heat transfer coefficient was done through two regions, the
first called the front region, which faces the fan, and the second called the wake or
backward region in which vortices were generated and built-up. A variance of
temperature was recognized between these two regions in such a way that front
heat transfer coefficient was higher than that for backward region.
The analysis of the present work is based on Reynolds number which is change
from 12894 to 33282 depends on the velocity of the used fan. The experimental
results of this study were compared with Kendoush analytical correlation (1995)
together with a number of certain other mathematical equations obtained from the
literature. It was found that this comparison was good especially at higher
temperatures.
Keywords
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