Flow of a Dusty Gas between Rotating Cylinders

Abstract

IN a recent article, Sproull¹ describes some experiments in which he measured the torque with air in a rotating cylinder viscometer and found a significant reduction of torque when the air was dusty. He attributes this to the viscosity of dusty air being less than that of clean air because the dust particles reduce the mean free path of the air molecules. However, this explanation is difficult to understand, and in any event contradicts the Einstein formula² for the viscosity of a suspension, according to which the viscosity will increase in proportion with the bulk concentration of the dust.