Vertical annular flow characteristics for air/silicone oil system

Al-Aufi, Yousuf Abdullah (2018) Vertical annular flow characteristics for air/silicone oil system. PhD thesis, University of Nottingham.

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Annular flow is one of the most common two-phase flow regimes observed in industrial applications. In annular flow, the liquid flows partly as a thin film along the pipe wall and partly as droplets entrained in the turbulent gas core. Most of the previous studies about the characteristics of annular flow and the developed correlations were conducted using an air/water system. This thesis reports an investigation about the characteristics of the annular flow regime and a development of liquid film thickness measurement using an ultrasonic technique in air/water and air/silicone oil systems.

Experiments were carried on an upward vertical annular flow test facility with 34.5 mm inner diameter (ID) using air/water and air/silicone oil two-phase systems. Time-varying of total pressure drop, liquid film thickness and wall shear stress were measured. The total pressure drop was measured using a remote seal differential pressure transducer and the wall shear stress was measured using a glue-on hot film sensor.

An ultrasonic technique was developed to measure the liquid film thickness. It was evaluated using static and dynamic measurements. For static measurements, it was compared with the liquid film thickness calculated based on knowledge of liquid volume and area of the test rig. For dynamic measurements, it was compared with two well-known conductance measurement techniques (Multi Pin Film Sensor and concentric probe) in falling film and upward vertical annular flow test facilities respectively. The relative error between the ultrasonic technique and the other two techniques was within ±5%. A new processing method for ultrasonic measurement called Baseline removal method was developed for measuring liquid film thickness less than 0.5 mm.

The influence of gas and liquid superficial velocities, viscosity and surface tension on the measured parameters was studied using both systems. Both systems showed similar trend behavior with increasing gas and liquid superficial velocities even there was a difference in fluid properties. The results were also compared with the existing correlations developed using an air/water system to predict each one of the measured parameters. Most of the tested correlations predicted the total pressure drop, liquid film thickness and wall shear stress with relative deviation of ±50% or even higher in some cases.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Hewakandamby, B.
Watson, N.J.
Dimitrakis, G.
Azzopardi, B.J.
Keywords: Annular flow, Pressure Drop, Wall shear stress, Liquid film thickness
Subjects: T Technology > TA Engineering (General). Civil engineering (General) > TA 357 Fluid mechanics
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 49216
Depositing User: AlAufi, Yousuf
Date Deposited: 13 Jul 2018 04:40
Last Modified: 13 Jul 2020 04:30

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