| Gas-liquid contacting plays an important role in many fields such as; biotechnology, energy conversion, separation technologies, multiphase chemical reactors, nanotechnology, oil and gas sector to outline a few. They are also encountered in many physical processes such as rain formation, bubble motion in sea water, gas movement in lava flows, seepage of natural gas in shallow and deep water etc.;The current thesis work aims towards developing a stepwise "geometry independent methodology" for the CFD simulation of gas-liquid flows/multiphase operations with minimum empiricism.;The aforementioned objective was accomplished by using an iterative step wise approach to simulate simple hydrodynamics of pipe flows over a large database of 454 points that covers a wide range of experimental conditions (fluid velocities up to 2.5 m/s, NRe 45,000-210,000, local energy dissipation rates of 0.01-1 W/kg, gas holdup of 4-25%, bubble sizes of 100mum to 20 mm) to correctly identify the pertinent momentum closures and PBE kernels that affect the accuracy of the current approach. A good agreement was achieved for all the fluid flow characteristics and dispersion behaviour provided the effect of coalescence retardation behaviour was accounted for.;Finally, the validity of the developed closures to correctly predict the hydrodynamics, dispersion characteristics and mass transfer performance was then tested on complex flow situation encountered in bubble columns and on air lift reactors operating on tap water and in the presence of alcohols which resulted in a good agreement with experimental measurements across the flow regimes. The developed methodology can thus be used to predict hydrodynamics and dispersion behaviour accurately for gas-liquid operations in any contactor provided that the coalescence retardation factor associated with the particular gas/liquid system can be determined or predicted.;The ability to accurately design these processes with higher efficiency and smaller volumes is of vital importance as it will beneficially impact the operational safety and reduce the environmental impact through the lowering of by-product formation. Traditionally, the local approaches such as drift flux were used but its usage proved to be ineffective in developing a general methodology which can be used to model any complex flow situation in hand. On the other hand, Computational fluid dynamics [CFD] can be effectively used to design units as it has the potential to account for all the complexities and the tendency of the dispersed phase to coalescence into larger entities in low energy dissipation regions. However, the success of the approach is limited by the lack of knowledge of correct momentum closures, bubble breakage/coalescence kernels and ability to account for the effect of coalescence retardation due to the presence of system impurities. |
