Non‐invasive experiments on the fluid film behavior in a horizontal rotating cylinder

Abstract

Subject of our investigations is the spatial distribution of a Newtonian liquid within a partially filled horizontal rotating hollow cylinder in dependence of the variables angular velocity and angular acceleration, cylinder filling and cylinder geometry as well as viscosity of the liquid. We focus on the development of a thin liquid film at the inner cylinder wall. The layer thickness was measured using a non‐invasive laser‐induced fluorescence measurement technique. In addition, the liquid distribution and flow topologies were observed and described using optical measurements.The occurring liquid distributions can be distinguished in three different states. At low angular velocities most of the liquid is located at the bottom area of the cylinder. However, a thin liquid film is always pulled out of the reservoir from the rotating cylinder wall. With increasing angular velocity more and more liquid is deflected and the locally measured film thickness increases. Exceeding a critical angular velocity, a centrifuged distribution of the whole liquid establishes. In this state the measured film thickness fits the theoretical calculated value quite well. Very complex liquid distributions and flow patterns develop in particular at critical angular velocities. In detail, at all investigated cylinder systems two critical angular velocities were verifiable, the so‐called transition points of liquid distribution. At the first critical velocity, the centrifuged state develops. With deceleration of the system a second critical angular velocity exists. Below this value the centrifuged distribution of the liquid collapses and moves back again to the bottom of the cylinder. A thin film is still pulled out of this reservoir. The second critical angular velocity of the break down is always smaller compared to the first one at which the centrifuged state develops. Both of them can be influenced using the investigated parameters. Eventually, we show that the locally measured film thickness also depends on these parameters.