By means of four ultrasonic transducers, we have measured the velocity of an accelerating sphere as it falls in water/fine solid particle suspensions. The fluids tested were silica dioxide suspensions and carbon black suspensions. The concentrations of silica dioxide suspensions were 0.3, 0.5 and 1.0wt% and those of carbon black suspensions were 0.3 and 0.5wt%. Four spheres between 57.1mm and 152.4mm in diameter were tested. From the experimental results, it was shown that the fall velocity of a sphere in suspensions is higher than that in tap water within a certain range of Reynolds numbers. Drag reduction does not occur above the critical Reynolds number.
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