Terminal Velocities of Balls dropping through Dilute Colloid Solutions

Abstract

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.