Investigation of the influence of free convection on the heat transfer of cylinders with different aspect ratios |
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Authors: | C Henselowsky H C Kuhlmann and H J Rath |
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Affiliation: | (1) ZARM - University of Bremen, 28359 Bremen, Germany |
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Abstract: | Electrically heated cylindrical wires are used in research and industry for fluid velocity and turbulence measurements. At
very low free-stream velocities (u≤0.1 m/s), hot-wire measurements are significantly influenced by buoyant convection. Below
a certain Reynolds number Re* this effect degrades the accuracy of the measurements. To assess the contribution of free-convection
heat transfer to the heat balance of hot-wires in cross flow, measurements under normal gravity and microgravity (μg) conditions
are compared keeping all other parameters constant. Under gravity conditions, the acceleration of gravity, the hot-wire axis
and the direction of the free stream are all perpendicular to each other. The microgravity experiments were carried out in
the Drop-Tower Bremen in which the residual acceleration is less than 10−5 g during a period of 4.7 s. The present investigation is concerned with a velocity range of 0≤u≤0.35 m/s corresponding to
a Reynolds number range Re<0.1 in standard air. This range includes pure free convection for Re→0 and forced-convection-dominated
heat transfer for Re=0.1. At intermediate Reynolds numbers both transport mechanisms must be considered. |
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Keywords: | |
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