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End effects in falling-ball viscometry

Published online by Cambridge University Press:  28 March 2006

R. I. Tanner
R. I. Tanner
Affiliation:
Department of Mechanical Engineering, University of Sydney
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Abstract

A calculation taking into account the interaction of tube wall and ends with a falling sphere is presented, with a view to assessing the change in drag on the sphere due to the end proximity in practical viscometry. It is shown that when the sphere is more than one fall tube radius from the closed end, the extra drag resulting is less than 4·5 × 10−3 of the Faxèn drag, and is therefore usually negligible.

For smaller end-sphere distances the end-effect drag increases rapidly, reaching about 1·5 of the Faxèn drag when the sphere centre is 0·25 tube radius from the end. The drag curve lies substantially below that given by Ladenburg (1907). Satisfactory agreement with experiment is found. It is concluded that with the commonly used types of fall tubes, end effects due to a closed end and an open surface will not be detectable.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 17 , Issue 2 , October 1963 , pp. 161 - 170
Copyright
© 1963 Cambridge University Press

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