Predictive models for gas-liquid two phase flows: investigating dependence on liquid phase viscosity

Fayyaz, Ahad (2023) Predictive models for gas-liquid two phase flows: investigating dependence on liquid phase viscosity. PhD thesis, University of Nottingham.

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The effect of inclination angle of pipe test section and liquid viscosity of silicone oil on flow development (i.e. flow regimes and transitions) and flow characteristics are studied in this thesis. The flow characteristics that are studied include liquid holdup, structure velocity and structure frequency. Intermittent flows such as slug, cap bubbly and churn usually present a pattern in which a gas dominated structure is followed by a liquid dominated structure. For given set of superficial properties, the pattern repeats with a characteristic mean frequency.

By investigating the effect of viscosity on two-phase characteristics, the present thesis will tackle many research gaps or areas of reverification. From literature survey, it was quite evident that there is limited readily available data for medium to high viscosity therefore this present investigation will increase the breadth of medium to high viscosity datapoints in literature. Moreover, another research gap that is tackled by this thesis is the reverification of trends of various flow characteristics with viscosity. Finally, another area of improvement that is brought up by this thesis is development of general liquid holdup correlation and flow regime maps with promising results. Therefore, the present study will provide a good contribution to the research on gas-liquid two-phase flow in circular pipes. It must also be stated that effect of viscosity has been overlooked in most of the experiments in literature as they mostly used water as the liquid phase. Even though there are several campaigns (in literature) using higher liquid viscosities, the number of data points is not sufficient to make any meaningful estimate of the influence it has on the flow regimes.

An inclinable rig was used to investigate gas – liquid two – phase flow. The rig is installed with a tilting boom, allowing upward two – phase flow to be investigated at different angles from horizontal. Three different viscosities (64 cP, 91.5 cP and 236 cP) of silicone oil were investigated. The gas phase for all these runs was air. The facility at the University of Nottingham was operated at atmospheric pressure. For each viscosity, different gas and liquid superficial velocities were experimented. The void fraction data was obtained for each set of conditions for 60 seconds using Electrical Capacitance Tomography (ECT).

The effect of inclination angle and viscosity on flow characteristics were firstly reported. The main findings can be summarised as that liquid holdup increases with liquid viscosity for a given gas and liquid superficial velocity. For a considerable change in liquid holdup, the change in viscosity must be large enough (100s of cP or so). Moreover, structure velocity also increased with liquid viscosity as well however the increase is small in comparison to that of liquid holdup. Drift flux modelling was also carried out. The range of distribution coefficient was 1.27 for 64 cP to 1.44 for 236 cP. The range of drift velocity decreases from 0.37 m/s for 64 cP to 0.32 m/s for 236 cP while Froude number ranged from 0.45 for 64 cP to 0.40 for 236 cP.

Additionally, for each inclination angle tested, a single dimensionless flow regime map was constructed, illustrating the effect of viscosity on flow regime transitions. The dimensionless number utilised was the Reynolds number. It was shown that, in comparison to utilisation of superficial velocities, Reynolds number produced much more promising results in terms of providing clear non-overlapping transition boundaries. Literature was also reviewed for horizontal and vertical orientation in order to create dimensionless flow regime maps for historical datasets.

Finally, a general liquid holdup correlation was developed using datasets from the present study and the literature. The development of model utilised a total of 2478 data points. After the development stage, further 2237 data points were tested against model presented in this study. In both scenarios, model presented in this study yielded promising results when compared to other models obtained from the literature.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Hewakandamby, Buddhika
Muljadi, Bagus Putra
Omar, Rajab
Keywords: viscosity, flow regimes, inclination angle, liquid holdup, correlation, structure velocity, structure frequency, drift flux
Subjects: T Technology > TA Engineering (General). Civil engineering (General) > TA 357 Fluid mechanics
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 73642
Depositing User: Fayyaz, Ahad
Date Deposited: 21 Jul 2023 04:40
Last Modified: 21 Jul 2023 04:40

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