Self-oscillatory loop flow of an external air-lift loop

Abstract

• Downcomer subjected to either annular or core jet impingement at low liquid levels. • Slug flow regime in the riser leads to regular and periodic loop liquid oscillations. • The downcomer’s slug flow with Taylor bubbles is the result of the riser’s churn flow. • Longer and smaller peak oscillations together forms a cycle of the oscillatory flow. • FFT, scatter and time delay plots are the tools to examine the excursive behavior. The present experimental investigation revealed that the hydrodynamic behavior of the external air-lift loop deviates significantly from its normal behavior when it is operated under low liquid inventory. To capture this excursive behavior a micro-processor based magnetic flowmeter is placed in line with the downcomer and recorded the temporal loop flow rate variation. The loop flow signals are analyzed rigorously using different techniques of nonlinear dynamics such as FFT, scatter, and time delay plots along with visual observations. Investigations show that with the increase in the rate of air injection in the riser, oscillations of loop liquid flow rate through the downcomer increases, and its behavior shifts from a periodic to chaotic nature. The diversity in loop liquid flow rate in the downcomer has the major influence on flow regime formation in the riser and a clear transformation is observed visually from slug flow to churn flow.