Asymmetries, co-current flow and interaction of Taylor drops rising in vertical tubes
Başlık:
Asymmetries, co-current flow and interaction of Taylor drops rising in vertical tubes
Yazar:
Direito, Filipe José Neto, author.
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (181 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-07C.
Özet:
There is an increasing interest in multiphase flow patterns due to their relevance in several operations in industrial processes. The aim of the present work was to improve the knowledge of an important multiphase flow pattern: slug flow in liquid-liquid vertical tubes. The strategy defined was based on three pillars: tools, design of testing conditions and assessment of the elementary flow characteristics. Regarding the tools, Computational Fluid Dynamics (CFD) was chosen due to its exibility and ease of use. Some lab experiments were also conducted, but only to validate the numerical results. The design of testing conditions followed a dimensional analysis that yielded relevant dimensionless numbers representing the forces involved in the flow. Finally, concerning the strategy to understand the phenomena, the first simulations were conducted with the simplest element in the flow: an axisymmetric Taylor drop rising in a tube filled with a denser stagnant liquid. Afterwards, complexity was added and the results interpreted (drop asymmetries, owing continuous phase and drops interaction).
For drops rising in stagnant continuous phase, the results showed that interfacial tension and viscous forces decrease drop velocity, while buoyancy has the opposite effect. The disturbed distance in the continuous phase below the drop depends mainly on the drop Reynolds number, being small for axisymmetric drops. Regarding asymmetries, three different behaviors were found: an axisymmetric region, an asymmetric region for small viscosity ratios and an asymmetric region for high viscosity ratios.
By the insertion of co-current, the balance between gravity and convective co-current effects was found to be determinant to the drops behavior. Furthermore, the increase of the continuous phase velocity promotes inertial effects and the appearance of closed recirculations regions below the drop. High enough continuous phase velocity also caused the inner portion (near the tube axis) of the continuous phase to move, in average, at the drop velocity. A pre-existing gas-liquid correlation that predicts drop velocity was adapted according to the results of this work. Moreover, it is observed that the increase of the viscosity ratio approximates the macro scale data to a limit defined by micro scale behavior. Interaction of two drops in axisymmetric conditions is very limited.
Due to the difficulties presented by asymmetric behavior, it was not possible to reach a full descriptive model for liquid-liquid slug flow. Hence, future work concerns overcoming challenges such as the serpentine-like effect found in some asymmetric ranges due to its importance in petroleum industry. More work is also required to produce enough data to develop a one-dimensional code able to easily predict liquid-liquid slug flow behavior.
In general, the present work succeeded in producing important knowledge regarding liquid-liquid slug flow.
Notlar:
School code: 5896
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(678861.1) | 678861-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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