Analysis on annular flow of liquid transported through a partially filled axially rotating pipe

In rotary tube reactors, rotary evaporators, or rotary atomizers, liquid is transported through a partially filled axially rotating pipe. The flow is annular when the pipe rotation is fast enough, as in most engineering applications; in this research, we investigated the steady and transient behavior of annular flows in a partially filled axially rotating pipe. First, the governing equations of a laminar annular flow were derived, solved, and verified. Then, the theory was used to study the transient flow behavior. The responses of the outlet flowrate to inlet flowrate variations and pressure fluctuations were investigated. To clarify the system parameters in which the theory holds, we also conducted experiments to find flow mode boundaries between the non-annular flow and the annular flow. Steady state solutions of the theory were then used to find system parameters in which the flow is laminar. The effects that a screw inserted inside the pipe has, on both the flow mode boundaries and the transient flow characteristics, are also demonstrated. To the best of our knowledge, this is the first inspection of the transient characteristics of an annular flow and the effects of an inserted screw on this type of flow.