Gas rising through a large diameter column of very viscous liquid: Flow patterns and their dynamic characteristics. (July 2019)

• Record Type: Journal Article
• Authors: Hasan, Abbas H.; Mohammed, Shara K.; Pioli, Laura; Hewakandamby, Buddhika N.; Azzopardi, Barry J.
• Is Part Of: International journal of multiphase flow. Volume 116(2019)
• Page Start: 1
• Page End: 14
• Publication Date: 2019-07
• Subjects: Flow patterns -- High viscous liquid -- Bubbly to slug and slug to churn transition -- Large pipe diameter -- Electrical Capacitance Tomography; Multiphase flow -- Periodicals; Écoulement polyphasique -- Périodiques; Multiphase flow; Periodicals; 620.1064
• DOI: 10.1016/j.ijmultiphaseflow.2019.04.001
• Languages: English
• ISSNs: 0301-9322

Abstract

Highlights: Flow characteristics of gas rising in a 240 mm column of 360 Pa s oil were studied. Mechanism of bubble bursting and liquid rupturing at the top surface was investigated. Unlike water, Taylor bubbles in 360 Pa s oil are ellipsoidal with rounded lower end. Slug/churn transition occurs due to flooding of the film around Taylor bubbles. Slug to churn transition are not deterministic but probabilistic (gradual). Abstract: Gas-liquid flows are affected strongly by both the liquid and gas properties and the pipe diameter, which control features and the stability of flow patterns and their transitions. For this reason, empirical models describing the flow dynamics can be applied only to limited range of conditions. Experiments were carried out to study the behaviour of air passing through silicone oil (360 Pa.s) in 240 mm diameter bubble column using Electrical Capacitance Tomography and pressure transducers mounted on the wall. These experiments are aimed at reproducing expected conditions for flows including (but not limited to) crude oils, bitumen, and magmatic flows in volcanic conduits. The paper presents observation and quantification of the flow patterns present. It particularly provides the characteristics of gas-liquid slug flows such as: void fraction; Taylor bubble velocity; frequency of periodic structures; lengths of liquid slugs and Taylor bubbles. An additional flow pattern, churn flow, has been identified. The transition between slug and churn has been quantified and the mechanism causing it are elucidated with the assistance of a model for the draining of the liquid film surrounding the Taylor bubble once this has burst through the top surface of the aerated column of gas-liquid mixture. It is noted that the transition from slug to churn is gradual.