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Terminal Velocities of Balls dropping through Dilute Colloid Solutions


WHITE1 has reported drag reduction of spheres in the Reynolds number range of 104 to 105 in equimolar mixtures of an association colloid cetyl–trimethyl ammonium bromide and α-naphthol. We have repeated his experiments using a range of steel, brass, glass and plastic balls and the same gel using concentrations of 650, 520 and 360 p.p.m., but do not detect any drag reduction. The balls were dropped down a ‘Perspex’-fronted tank nine feet high and the terminal velocities measured by a photographic technique of Ulherr et al.2. A range of sphere Reynolds numbers of 8.2 × 103 to 3.3 × 105 was obtained basing the kinematic viscosity in the Reynolds number on measurements taken for each gel in an Ostwald viscometer.


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WHITE, D., BOND, J. Terminal Velocities of Balls dropping through Dilute Colloid Solutions. Nature 226, 72 (1970).

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