Author: Zhe Cui Publisher: ISBN: Category : Bubbles Languages : en Pages :
Book Description
Abstract: Bubble columns are widely used as multiphase reactors in chemical industries due to many advantages. The transport behavior in these systems is complex and a comprehensive knowledge of the transport phenomena, including hydrodynamics and turbulence properties are required. The hydrodynamics in a high pressure bubble column is experimentally investigated. The liquid velocities are measured using a LDV (Laser Doppler velocimetry). The Reynolds stresses are obtained. The effect of the pressure on the transition of the flow regime, flow field and the Reynolds stresses are studied. Furthermore, the effects of the liquid properties on the hydrodynamics of the bubble column are discussed. The turbulence energy distributions in the bubble columns are investigated using the LDV and PIV. The energy containing ranges for the bubble-induced and shear-induced turbulence are determined from the power spectra. Experimental results indicate that the bubble-induced turbulence dominates over the shear-induced turbulence under the operating conditions. The bubble-induced turbulence includes the turbulence in the bubble wake and that from the drift velocity change. The interaction between two turbulence field can only be observed when the turbulence in both fields is strong and the interaction tends to enhance the turbulence in both fields. The liquid phase turbulence is enhanced in the presence of particles at high superficial gas velocities while it is attenuated under low superficial gas velocity conditions. A criterion based on the variation of the ratio, Ug(r)/umf is proposed to account for the effect of the solids on the liquid phase turbulence. The prediction based on this criterion matches well with the experimental results. The behavior of a 6 mm mesobubble in an acoustic standing wave field is examined both experimentally and numerically. The acoustic standing waves at 16 kHz and 20 kHz are generated using two Nickel magnetostrictive transducers. The bubble rise velocity is significantly lower than that in the absence of an acoustic field. The behavior of bubble volume contraction and expansion can be accounted for by a 3-D direct numerical simulation of the bubble dynamics and flow field based on the compressible N-S equations coupled with the level-set method.
Author: Subrata Kumar Majumder Publisher: CRC Press ISBN: 1351249843 Category : Science Languages : en Pages : 151
Book Description
Slurry bubble column reactors are intensively used as a multiphase reactor in the chemical, biochemical, and petrochemical industries for carrying out reactions and mass transfer operations in which a gas, made up of one or several reactive components, comes into contact or reacts with a liquid. This volume describes the hydrodynamics of three-phase gas-liquid-solid flow in a downflow slurry bubble column. The efficiency of the downflow gas interacting system is characterized by the self-entrainment of secondary gas. The book covers the gas entrainment phenomena, gas holdup characteristics, pressure drop, gasliquid mixing characteristics, bubble size distribution, interfacial phenomena, and the mass transfer phenomena in the downflow slurry system. This volume will be useful in chemical and biochemical industries and in industrial research and development sectors, as well as in advanced education courses in this area. The book will be helpful for further understanding the multiphase behavior in gas interacting multiphase systems for research and development. The hydrodynamic and mass transfer characteristics discussed will be useful in the design and installation of the modified slurry bubble column in industry for specific applications.
Author: Subrata Kumar Majumder Publisher: Elsevier ISBN: 012803288X Category : Science Languages : en Pages : 464
Book Description
Hydrodynamics and Transport Processes of Inverse Bubbly Flow provides the science and fundamentals behind hydrodynamic characteristics, including flow regimes, gas entrainment, pressure drop, holdup and mixing characteristics, bubble size distribution, and the interfacial area of inverse bubble flow regimes. Special attention is given to mass and heat transfer. This book is an indispensable reference for researchers in academia and industry working in chemical and biochemical engineering. Hydrodynamics and Transport Processes of Inverse Bubbly Flow helps facilitate a better understanding of the phenomena of multiphase flow systems as used in chemical and biochemical industries. - A first book in the market dedicated to the hydrodynamics of inverse bubbly flows - Includes fundamentals of conventional and inverse bubble columns for different hydrodynamic parameters - Includes recommendations for future applications of bubble flows
Author: Wolf-Dieter Deckwer Publisher: John Wiley & Sons ISBN: Category : Science Languages : en Pages : 564
Book Description
This technology, though used for many years, has shown great vitality recently and is still in a state of flux. Provides an account of developments up to the present and also an orderly evaluation of literature already published on the subject. Considerable space is devoted to bubble column reactor performance predictions based on mathematical models and the importance of each is explained with practical examples.
Author: Onkar N. Manjrekar Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 101
Book Description
Bubble columns and slurry bubble columns are multiphase reactors used for a wide range of applications in the biochemical, chemical, petrochemical, and metallurgical industries. In spite of their widespread usage, the scale-up of bubble columns remains an ongoing challenge. Various scale-up approaches, based on concepts ranging from ideal mixing to complex 3-D multiphase CFD models, have been used for assessing the effect of column size and gas and liquid flow rates on column hydrodynamics and reactor performance. Among these approaches, phenomenological models based on either single-class or multi-class bubbles that were validated on cold flow systems have been successful in predicting the residence time distributions of gas and liquid in pilot-scale bubble columns (Chen et al., 2004) (Gupta, 2002). However, such models are not entirely predictive, since they are validated using columns having the same size as hot operating units. To provide better predictive capability, we need prior knowledge of local hold-up, transport coefficients, and bubble dynamics. This dissertation provides an improved understanding of the key design parameters (gas hold-up, volumetric mass transfer coefficients, gas-liquid interfacial area, and their spatial distribution) for predictive scale-up of bubble columns. In this work, a 4-point optical probe is used to estimate local gas hold-up and bubble dynamics (specific interfacial area, frequency, bubble velocity, and bubble chord-lengths) and their radial profiles in a cold-flow slurry bubble column and a bubble column photo-bioreactor. Along with local bubble dynamics, the effect of superficial gas velocity on volumetric mass transport coefficients in several sizes of bubble columns, with and without internals, and in slurry bubble columns and photo-bioreactors are studied. Key findings: In the bubbly flow regime, bubble dynamics in photo-bioreactors with suspended algae were dominated by the physicochemical properties of the liquid, as distinguished from the churn-turbulent flow regime in the slurry bubble columns, where bubble dynamics were mainly affected by turbulent intensities. In the bubbly-flow regime, volumetric mass transfer coefficients increased with an increase in superficial gas velocity. However, in the churn-turbulent flow regime, they approached a constant value with an increase in the superficial gas velocity. A new methodology was proposed to identify the flow regime from optical probe signals based on the support vector machine algorithm, which can uniquely classify flow regimes for various systems on a single flow regime map. A new model for the liquid phase mixing, that with a proper choice of the mass transfer coefficients enables a good match of the predicted and measured tracer response is described. This model provides a better prediction of volumetric mass transfer coefficients than the currently used well mixed model for the liquid phase (CSTR). The dissertation improves the fundamental understanding of the connection between bubble dynamics and mass transfer. Using the 4-point optical probe as a tool, it demonstrates a connection between bubble dynamics and volumetric mass transfer coefficients. Present work addresses the need of industries to have a method that can be used as an online process control tool to identify flow regime, this method has been tested at cold flow conditions and needs to be implemented at hot flow conditions. The parameters (radial distributions of gas hold-up, bubble velocities, and volumetric mass transfer coefficient) that are evaluated in the present work can be used to validate phenomenological models and CFD results at cold flow conditions, which can later be combined with process chemistry to accomplish scale-up (Chen et al., 2004). The open literature on multiphase reactors is mainly limited to cold flow condition, and techniques such as the optical probe need to be extended to hot flow conditions. The optical probe described here can withstand high temperature and pressure, but for hot flow conditions it requires a better binding agent to hold the probe tips together, one that will not dissolve in industrial solvents.
Author: Liang-Shih Fan Publisher: Butterworth-Heinemann ISBN: 1483289508 Category : Science Languages : en Pages : 380
Book Description
This book is devoted to a fundamental understanding of the fluid dynamic nature of a bubble wake, more specifically the primary wake, in liquids and liquid-solid suspensions, an dto the role it plays in various important flow phenomena of multiphase systems. Examples of these phenomena are liquid/solids mixing, bubble coalescence and disintergration, particle entrainment to the freeboard, and bed contraction.
Author: Abbas Jawad Sultan Publisher: ISBN: Category : Languages : en Pages : 277
Book Description
"Understanding the hydrodynamics of bubble columns with and without vertical heat-exchanging tubes is a necessity for the proper design, scale-up, and operation of these reactors. To achieve this goal, systematic experiments were performed to visualize and quantify the influence of the presence of vertical internal tubes on the gas holdup distributions and their profiles, axial liquid velocity, and turbulent parameters (i.e., normal and shear stresses; turbulent kinetic energy) by using advanced gamma-ray computed tomography (CT) and radioactive particle tracking (RPT). In this study, the experiments were conducted in 6- and 18-inch bubble columns with an air-water system as the working fluid, under a wide range of superficial gas velocities (5-45 cm/s). Three configurations of vertical internals (i.e., hexagonal, circular without a central tube, and circular with a central tube plus vertical internals), as well as the vertical internals sizes, were examined in this study. These three configurations were designed to cover 25% of the column's cross-sectional area (CSA) to represent the percentage of the covered area utilized in the Fischer-Tropsch process. Reconstructed CT images reveal that the configurations of the vertical internal tubes significantly impacted the gas holdup distribution over the CSA of the column. Additionally, the bubble column equipped with 1-inch vertical internals exhibited a more uniform gas holdup distribution than the column with 0.5-inch internals. Moreover, a remarkable increase in the gas holdup values at the wall region was achieved in the churn turbulent flow regime due to the insertion of vertical internals inside the column. Furthermore, pronounced peaks of the gas holdup and axial liquid velocity were observed in the inner gaps between the vertical internals"--Abstract, page iv.
Author: Mohd Shahimie Selamat Publisher: ISBN: Category : Bubbles Languages : en Pages : 42
Book Description
The applications of bubble columns are very important as multiphase contactors and reactors in process industry. They are wide and extensively used in chemical, petrochemical and biochemical industries. The advantages of bubble column are low maintenance and operating cost due to the compactness and no moving part. They also have an excellent mass and heat transfer characteristic or high heat and mass transfer coefficients, and high durability of catalyst or packing material. It is important to understand the nature of hydrodynamics and operational parameters to characterize their operation including pressure drop, gas superficial velocity, bubble rise velocity, etc., to do the design and scale-up process. Although experimental methods are available to elucidate the multiphase flow in bubble column by the means of advanced experimental methods i.e. X-ray tomography and laser doppler anemometry, the experimental setup is often expensive to develop. Alternatively, the computational fluid dynamics can be used to evaluate the performance of bubble column at lower cost compared to experimental setup. In this work commercial CFD software, FLUENT 6.3 was employed for modeling of gasliquid flow in a bubble column. Multiphase simulations were performed using an Eulerian-Eulerian two-fluid model and the drag coefficient of spherical and distorted bubbles was modeled using the Tomiyama (1995) and Schiller-Naumann (1935) models. The effect of the void fractions on the drag coefficient was modeled using the correlation by Behzadi (2004). The CFD predictions were compared to the experimental measurement adopted from literature. The CFD predicts the turbulent kinetic energy, gas hold-up and the liquid axial velocity fairly well, although the results seem to suggest that further improvement on the interfacial exchange models and possibly further refinement on the two-fluid modeling approaches are necessary especially for the liquid axial velocity and turbulent kinetic energy. It is clear from the modeling exercise performed in this work that CFD is a great method for modeling the performance of bubble column. Furthermore, the CFD method is certainly less expensive than the experimental characterization studies.
Author: Doraiswami Ramkrishna Publisher: Elsevier ISBN: 0080539246 Category : Science Languages : en Pages : 373
Book Description
Engineers encounter particles in a variety of systems. The particles are either naturally present or engineered into these systems. In either case these particles often significantly affect the behavior of such systems. This book provides a framework for analyzing these dispersed phase systems and describes how to synthesize the behavior of the population particles and their environment from the behavior of single particles in their local environments. Population balances are of key relevance to a very diverse group of scientists, including astrophysicists, high-energy physicists, geophysicists, colloid chemists, biophysicists, materials scientists, chemical engineers, and meteorologists. Chemical engineers have put population balances to most use, with applications in the areas of crystallization; gas-liquid, liquid-liquid, and solid-liquid dispersions; liquid membrane systems; fluidized bed reactors; aerosol reactors; and microbial cultures. Ramkrishna provides a clear and general treatment of population balances with emphasis on their wide range of applicability. New insight into population balance models incorporating random particle growth, dynamic morphological structure, and complex multivariate formulations with a clear exposition of their mathematical derivation is presented. Population Balances provides the only available treatment of the solution of inverse problems essential for identification of population balance models for breakage and aggregation processes, particle nucleation, growth processes, and more. This book is especially useful for process engineers interested in the simulation and control of particulate systems. Additionally, comprehensive treatment of the stochastic formulation of small systems provides for the modeling of stochastic systems with promising new areas of applications such as the design of sterilization systems and radiation treatment of cancerous tumors. - A clear and general treatment of population balances with emphasis on their wide range of applicability. Thus all processes involving solid-fluid and liquid-liquid dispersions, biological populations, etc. are encompassed - Provides new insight into population balance models incorporating random particle growth, dynamic morphological structure, and complex multivariate formulations with a clear exposition of their mathematical derivation - Presents a wide range of solution techniques, Monte Carlo simulation methods with a lucid exposition of their origin and scope for enhancing computational efficiency - An account of self-similar solutions of population balance equations and their significance to the treatment of data on particulate systems - The only available treatment of the solution of inverse problems essential for identification of population balance models for breakage and aggregation processes, particle nucleation and growth processes and so on - A comprehensive treatment of the stochastic formulation of small systems with several new applications
Author: Zhe Cui
Author: Subrata Kumar Majumder
Author: Subrata Kumar Majumder
Author: Wolf-Dieter Deckwer
Author: Onkar N. Manjrekar
Author: Liang-Shih Fan
Author: 
Author: Abbas Jawad Sultan
Author: Mohd Shahimie Selamat
Author: Doraiswami Ramkrishna