A Study on the Effect ofNozzle Type on the Hydrodynamics of Ejector-Induced Cocurrent Upflow Bubble Column

Bubble columns as gas-liquid cocurrent contactors have gained a considerable attention due to various advantages they offer. The effectiveness of gas distributors in the bubble columns determines the mass transfer efficiency of the column. Ejector is one of the most widely used devices as the gas distributors in the bubble columns. Although empirical correlations for the ejectors have been reported in literature, no study based on the principle of fluid mechanics has been carried out on the effect of ejector geometry on its important hydrodynamic characteristics. A better understanding of the ejectors is essential for an improved design of the ejector itself and the bubble column. In the present work, the experimental setup consists of an ejector integrated with upflow bubble column and a gas-liquid separator at the top of the column. Experimental investigations have been carried out on the effect of ejector nozzle geometry on the hydrodynamics of cocurrent upflow bubble column. Gas entrainment rate, gas hold-up, pressure drop and energy dissipation for water-air system are studied and reported. Experiments have been conducted using convergent and orifice nozzles with different types and sizes. It is found experimentally that nozzle with smaller nozzle diameter develops higher vacuum and entrains more air as the suction fluid, for a given flow rate of water as the motive fluid. This also means that nozzle with smaller nozzle diameter gives higher gas hold-up and dissipates more energy to create intense mixing between the two phases. In terms of nozzle type, orifice nozzles present higher vacuum level than convergent nozzles for the same nozzle diameter. The pressure drop across the nozzle and the air entrainment rate have been modeled and analyzed by applying Bernoulli's principle. Predicted values of air entrainment rate as a function of water flow rate through the nozzle by the theoretical model developed show good agreementwith experimental values. Gas hold-up data has also been analyzed using drift flux model. The analysis agrees well with the previous works

Development of a dual optical fiber probe for the hydrodynamic investigation of a horizontal annular drive gas/liquid ejector

A dual-channel optical fiber probe was developed to quantify the bubble characteristics (void fraction, velocity, and bubble size) in a gas–liquid annular ejector system. Water is pumped upstream of the ejector contraction. Since a low pressure region exists downstream in the ejector diffuser, this permits air to be sucked into the flowing liquid by jet pump action and the inlet air volumetric flow rate is measured by a flow meter. Verification of the void fraction (range 0.15–0.5) measured by the optical fiber probe was then possible and deviations were generally around ± 5%. Also, bubble velocity was measured using the optical probe by cross-correlating signals from the two fibers whose tips are separated by a known distance. Alternatively measuring bubble velocity using a particle image velocimetry method provided validation for the optical fiber probe system where a high speed camera was used to capture instantaneous bubble images at time intervals of 0.125 ms. Excellent agreement between the velocities using both methods is reported. For bubble size measurements, analyzing the temporal signals from a single probe enabled estimation of the size of a bubble. Bubble sizes measured ranged between 1.5 and 6.0 mm and size distributions were constructed for different ejector water volumetric flow rates ranging from 0.0022 to 0.0063 m3/s. LabVIEW provided a convenient platform for coding the algorithms for estimating the void fraction, bubble velocity and bubble size. For further comparison, a CFD study of the ejector system was done, and the vertical radial profiles of the void fraction were compared with those obtained by the optical fiber system and these showed good agreement

Numerical Simulation of Bubble Coalescence and Break-Up in Multinozzle Jet Ejector

Designing the jet ejector optimally is a challenging task and has a great impact on industrial applications. Three different sets of nozzles (namely, 1, 3, and 5) inside the jet ejector are compared in this study by using numerical simulations. More precisely, dynamics of bubble coalescence and breakup in the multinozzle jet ejectors are studied by means of Computational Fluid Dynamics (CFD). The population balance approach is used for the gas phase such that different bubble size groups are included in CFD and the number densities of each of them are predicted in CFD simulations. Here, commercial CFD software ANSYS Fluent 14.0 is used. The realizable k-ε turbulence model is used in CFD code in three-dimensional computational domains. It is clear that Reynolds-Averaged Navier-Stokes (RANS) models have their limitations, but on the other hand, turbulence modeling is not the key issue in this study and we can assume that the RANS models can predict turbulence of the carrying phase accurately enough. In order to validate our numerical predictions, results of one, three, and five nozzles are compared to laboratory experiments data for Cl2-NaOH system. Predicted gas volume fractions, bubble size distributions, and resulting number densities of the different bubble size groups as well as the interfacial area concentrations are in good agreement with experimental results

A Study on the Effect ofNozzle Type on the Hydrodynamics of Ejector-Induced Cocurrent Upflow Bubble Column

Bubble columns as gas-liquid cocurrent contactors have gained a considerable attention due to various advantages they offer. The effectiveness of gas distributors in the bubble columns determines the mass transfer efficiency of the column. Ejector is one of the most widely used devices as the gas distributors in the bubble columns. Although empirical correlations for the ejectors have been reported in literature, no study based on the principle of fluid mechanics has been carried out on the effect of ejector geometry on its important hydrodynamic characteristics. A better understanding of the ejectors is essential for an improved design of the ejector itself and the bubble column. In the present work, the experimental setup consists of an ejector integrated with upflow bubble column and a gas-liquid separator at the top of the column. Experimental investigations have been carried out on the effect of ejector nozzle geometry on the hydrodynamics of cocurrent upflow bubble column. Gas entrainment rate, gas hold-up, pressure drop and energy dissipation for water-air system are studied and reported. Experiments have been conducted using convergent and orifice nozzles with different types and sizes. It is found experimentally that nozzle with smaller nozzle diameter develops higher vacuum and entrains more air as the suction fluid, for a given flow rate of water as the motive fluid. This also means that nozzle with smaller nozzle diameter gives higher gas hold-up and dissipates more energy to create intense mixing between the two phases. In terms of nozzle type, orifice nozzles present higher vacuum level than convergent nozzles for the same nozzle diameter. The pressure drop across the nozzle and the air entrainment rate have been modeled and analyzed by applying Bernoulli's principle. Predicted values of air entrainment rate as a function of water flow rate through the nozzle by the theoretical model developed show good agreementwith experimental values. Gas hold-up data has also been analyzed using drift flux model. The analysis agrees well with the previous works

Aeronautical Engineering: A continuing bibliography with indexes, supplement 137, July 1981

This bibliography lists 483 reports, articles, and other documents introduced into the NASA scientific and technical information system in June 1981

Severe slugging phenomenon and a novel method for its mitigation based on the Surface Jet Pump technology

Master's thesis in Offshore technology : industrial asset managementThe present thesis is focused on the problem of severe slugging and ways to mitigate it. Severe slugging is an oscillatory multiphase flow regime characterized by high variations in production rates occurring in offshore pipeline-riser systems. Chapter 1 provides basic notions related to multiphase flow, which are essential for understanding of the rest of the thesis. Chapter 2 gives a thorough description of the severe slugging occurrence mechanism and preconditions as well as introduces different types of the phenomenon. Special attention is given to the effect of mass transfer and how it alters the flow regime’s behavior. Detrimental effects of severe slugging are discussed and some examples are provided. Chapter 3, making a significant part of the thesis, provides its reader with carefully gathered data concerning severe slugging alleviation and mitigation methods published from 1973 to 2015, both conventional and purely speculative methods are discussed. Examples, where possible, are given. Chapter 4 considers modeling of severe slugging in a vertical riser with aids of the multiphase simulation program OLGA. A constructed study case is considered and described with some of the mitigation techniques implemented and tested. Chapter 5 evaluates a novel severe slugging mitigation method proposed by Caltec Ltd. UK. The method assumes pipeline system depressurization by installation of a Surface Jet Pump on the production platform. The chapter gives the method description and verifies its feasibility using a simulation model within OLGA. The thesis ends with Conclusions and Recommendations for further work and self-evaluation