Displacement flows in rotating pipes

Abstract

<h2>Abstract</h2> Displacement flows frequently occur in natural phenomena and industrial applications, e.g., in lung airways, oil well cementing, coating and cleaning of processing machinery. We study experimentally and numerically the effects of a pipe axial rotation on buoyant miscible flows in inclined pipes, while considering three cases of progressively increasing complexity: (i) Newtonian exchange flows (Lyu et al., 2020), (ii) Newtonian displacement flows (Lyu & Taghavi, 2018), and (iii) viscoplastic displacement flows (Lyu & Taghavi, 2020). We show how the flow dynamics is governed by an elegant balance among the characteristic velocities of the flow. We demonstrate that increasing the pipe rotation speed induces transverse mixing and results in a complete removal of the displaced fluid by the displacing fluid, above a critical rotation speed. Our findings offer insights on how to improve displacement efficiency using rotational motion.