Experimental investigation on excursive behaviour of an air-lift loop

Abstract

Air-Lift Loop exhibits an excursive behaviour when it is operated under low liquid inventory. To study this dynamic behaviour the loop circulation rate is measured in the downcomer by a magnetic flowmeter and the signals are analysed using different techniques of nonlinear dynamic analysis. This excursive behaviour is rigorously analysed through FFT and scatter plot techniques along with the help of recorded raw signals and visual observations. Investigations show that with the increase in the rate of air injection in the riser, oscillations of the flow rate through the downcomer increases and its behaviour shifts from periodic to chaotic nature. It is further noticed that the change of flow regime in the riser has a direct influence on the behaviour of ALL and change of periodic to random nature occurs when the flow regime in the riser changes to churn flow from slug flow.