Flow of water through fine clearances with relative motion of the boundaries

In practice in many cases of flow through fine annular clearances, the inner boundary consists of a bush keyed to a rotating shaft, and in the investigation about to be described, it was found that up to a certain critical speed of rotation the resistance to flow is unaffected, but above this speed the resistance increases as the speed increases. Curves are given by means of which the critical angular velocity and the resistance at higher angular velocities can be ascertained for the range of clearances investigated. 2.Apparatus . Two apparatuses, Nos. I and II, were used, each consisting in principle of a brass cylinder mounted on a shaft and capable of rotating inside a hollow cylinder, also of brass. The surfaces were finished as smooth as possible by grinding.