bluuebunny/crossref_metadata_2025 huggingface dataset:
Euler/Lagrange Calculations of Bubbly Flows with Consideration of Bubble Coalescence
Authors: Sommerfeld Martin , Bourloutski Evgueni , Bröder Dirk
Published: July 2010

A bubble coalescence model was developed on the basis of the Lagrangian approach, where bubbles are followed through the turbulent flow field along their trajectories. The collision process was described using a stochastic inter‐particle collision model. Coalescence occurred if the contact time became larger than the film drainage time. The film drainage time was determined by a simple formulation according to classical approaches, whereas the contact time resulted directly from the collision model. The performance of the model was analyzed for bubble rise in a prescribed homogeneous isotropic turbulence field. Moreover, numerical calculations by the coupled Euler/Lagrange approach were performed and compared with measurements in a bubble driven loop facility. The comparison showed reasonably good agreement for liquid and bubble velocities.
Bubble Breakup and Coalescence in a Plunging Liquid Jet Bubble Column
Authors: Atkinson Bruce W. , Jameson Graeme J. , Nguyen Anh V. , Evans Geoffrey M. , Machniewski Piotr M.
Published: July 2010

In this study the bubble size distribution and energy dissipation rate are measured in a plunging liquid jet bubble column. The maximum stable bubble diameter in the mixing zone was successfully predicted based on Weber number analysis. A Pareto analysis indicated that the coalescence of bubbles principally occurred as a binary process. The bubble number flux was modeled based on the bubble number concentration, collision frequency of two bubbles of the same diameter, and the probability of coalescence taking place. In general, the predictions were in good agreement with the measurements for both the mixing and pipe flow zones.
Bubble Column Bioreactors: Comparison with Stirred Fermenters Based on Local Gas Hold‐up Distribution
Authors: Vlaev Serafim D. , Fialova Marie
Published: July 2010

Local gas hold‐up in viscous aerated batches in bubble column and impeller gas dispersion devices was studied. Unlike the former analyses valid for water, the emphasis of this study was on gas hold‐up in relatively viscous and shear‐thinning liquids mimicking physically nutrient solutions from industrial fermentation practice. Gas hold‐up is correlated with viscosity, plasticity and shear‐inducing velocities. Vessels with ID 0.2‐0.4 m were studied. The prevailing parabolic type of radial profile specific for water was shown to change to a flat saddle type one with incidental peaks. Comparison with stirred vessels with two different impeller designs showed opposite effects. Possible control of gas dispersion efficiency by appropriate selection of gas dispersion devices is discussed.
Effect of Dispersion on Particle Segregation Due to Sparged Air in a Hydrocyclone
Authors: Liu Shijie , Zhu Zhengxiang , Masliyah Jacob H.
Published: July 2010

Fractionation of kraft wood pulp fibres was carried out in a hydrocyclone. Long fibres tend to migrate to the low shear region and report to the overflow stream. Excellent fractionation was found at high pulp slurry feed rates with a split ratio between 0.07 and 0.3. However, when air bubbles are sparged, all the fibres are more uniformly distributed inside the hydrocyclone. When increasingly more bubbles are present, on the other hand, long fibres drain down slower because of rapidly rising air bubbles. Thus, more long fibres report to the overflow stream at extremely high air injection rates.
Solid‐Liquid Mass Transfer and Hydrodynamics in the Hydrogenation of 4‐Nitrobenzoic Acid
Authors: Winterbottom Mike , Fishwick Rob , Stitt Hugh
Published: July 2010

Solid‐liquid mass transfer coefficients were determined in a stirred reactor for the hydrogenation of 4‐nitrobenzoic acid. The effects of the catalyst particle physical properties were investigated and the findings compared to the model system of aqueous dissolution of salicylic acid. In an attempt to explain these mass transfer observations the technique of positron emission particle tracking (PEPT) has been used to study the effect of different operating conditions on the liquid flow patterns and, in particular, the particle‐liquid slip velocities. Time‐averaged slip velocities were determined, thereby revealing information about particle‐liquid behaviour and zones of poor mass transfer in agitated reactors.
Quality of Mixedness Profiles Based on Spatial Distribution of Local Mass Transfer Coefficients in a Bubble Column
Authors: Nedeltchev Stoyan , Ookawara Shinichi , Ogawa Kohei
Published: July 2010

LocalkLameasurements were performed during physical absorption of carbon dioxide into deionized water in a 0.289 m diameter bubble column equipped with a perforated plate gas distributor (31 holes × ø 0.002 m, free plate area 0.15 %). Three superficial gas velocities (ug) were examined (0.018, 0.031 and 0.038 m/s) under clear liquid height of 0.56 m. The spatialkLadistributions were treated by the quality of mixedness (QM) algorithm. It was found that at the regime transition velocity (Utrans= 0.034 m/s) to churn‐turbulent flow regime both lower and upper column zones are characterized with the same QM indices.
Liquid Dispersion and Gas‐Liquid Mass Transfer in Three‐Phase Inverse Fluidized Beds
Authors: Kim Sang Woo , Kim Hyun Tae , Song Pyung Seob , Kang Yong , Kim Sang Don
Published: July 2010

Axial dispersion of continuous liquid phase and gas‐liquid mass transfer characteristics were investigated in a three‐phase inverse fluidized bed with viscous liquid medium. The axial dispersion coefficient of liquid phase(Dz) increased with increasing gas(UG) or liquid velocity(UL), but decreased with an increase in the viscosity of continuous liquid medium(µL). The volumetric gas‐liquid mass transfer coefficient(kLa) increased with increasing UG but decreased with increasing µL, while it did not change considerably with increasing UL : The effects of UG were dominant in three phase inverse fluidized beds. In the beds of polyethylene particle(relatively heavier particle), the values of Dz and kLa exhibited higher values than those in the beds of polypropylene particles(lighter particle). The values of Dz and kLa were well correlated in terms of operating variables.
Gas Holdup and Mass Transfer in a Three‐Phase Reversed Flow Jet Loop Slurry Reactor with Non‐Newtonian Fluids
Authors: Li Yongxiang , Wu Wei , Min Enze
Published: July 2010

Experiments were carried out to study the total gas holdup and mass transfer coefficient in a three‐phase reversed flow jet loop slurry reactor, with air, carboxymethyl cellulose (CMC) aqueous solution and resin as gas, liquid, and solid phases respectively. The distinct feature of this study is that the liquid employed was non‐Newtonian. The influences of reactor geometry, solid holdup, and operation parameters were studied and the optimum values of draft tube to reactor diameter ratio, solid holdup, and distance between the lower edge of the draft tube and the bottom plate, were found to be 0.45, 0.03 and 0.08 m, respectively. Empirical corrections for the total gas holdup and mass transfer coefficient were developed.
Using CFD to Describe the Hydrodynamics of Internal Air‐lift Reactors
Authors: Van Baten Jasper M. , Ellenberger Jürg , Krishna Rajamani
Published: July 2010

The hydrodynamics of three configurations of internal airlift reactors, two with riser diameters of 0.1 m and one with a riser diameter of 0.24 m, operating with air—water system, have been experimentally investigated for a range of superficial gas velocities. The experimental results are compared with a model using computational fluid dynamics (CFD) with Eulerian descriptions of the gas and liquid phases. Interactions between the bubbles and the liquid are taken into account by means of a momentum exchange, or drag coefficient based on a literature correlation. The turbulence in the liquid phase is described using the k‐ϵ model. The CFD model shows good agreement with the measured data on gas holdup, liquid velocity in the downcomer and in the riser for all three configurations. The developed CFD model has the potential of being applied as a tool for scaling up.
CFD Simulation of Residence Time Distribution and Mixing in Bubble Column Reactors
Authors: Ekambara Kalekudithi , Joshi Jyeshtharaj B.
Published: July 2010

A three‐dimensional CFD model has been developed to predict liquid phase velocities in bubble columns. An agreement was observed between the predicted and the experimental data available in the published literature. The validated CFD model has been extended for the simulation of macro‐mixing and hence the prediction of mixing time, RTD and dispersion coefficient. Liquid phase mixing time was measured in 0.2 and 0.4 m i.d. columns over a wide range of superficial gas velocity (0.07 to 0.295 m/s) and height‐to‐diameter ratio (2 to10). An agreement was observed between the CFD predictions and the experimental values of the mixing time as well as all the experimental data on dispersion coefficient published in the literature.
Oxidation of Tetrachloroethylene in a Bubble Column Photochemical Reactor Applying the UV/H2O2 Technique
Authors: Alibegic Dzevo , Tsuneda Satoshi , Hirata Akira
Published: July 2010

Mass transfer of tetrachloroethylene (PCE) gas, followed by a free‐OH radical reaction in the liquid phase, was studied in a bubble column reactor equipped with a UV light source and containing aqueous H2O2 as the reacting medium. Degradation of PCE in the liquid phase was found to follow pseudo‐first‐order kinetics, and the optimal ratio of H2O2/PCE leading to the highest oxidation rate could be successfully obtained from the analysis of the steady‐state OH radical concentration. Absorption of PCE gas was in the kinetic slow regime and could be predicted based on the ratio of the apparent rate constant of PCE liquid degradation to the volumetric mass transfer coefficient (kapp/KLa). The presence of small amounts of PCE in the liquid bulk had positive effect on the mass transfer over the range studied and need to be taken into account.
Comparison, Combination and Validation of Measuring Techniques for Local Flow and Turbulence Analysis in Bubble Columns and Airlift Reactors
Authors: Vial Christophe , Bendjaballah‐Lalaoui Nadia , Poncin Souhila , Wild Gabriel , Midoux Noël
Published: July 2010

The applicability of velocimetry techniques based on the Doppler effect — such as laser and ultrasound Doppler velocimetry — for investigating local hydrodynamics in bubble columns and airlift reactors have been extended to non‐coalescing media. Their limitations are highlighted, especially as a function of gas sparger and reactor type. The ultrasound technique was shown to be able to measure either bubble or liquid velocity. Differences in local hydrodynamics due to coalescence behaviour were used to support the analysis. Data validation was carried out both by mass balance and by comparison with other techniques, such as electrochemical probes, Pavlov tubes and optical probes.
Gas/Liquid Two‐phase Flow in a Flat Sheet Filtration Module: Measurement of Local Wall Shear Stresses
Authors: Ducom Gaëlle , Puech François‐Pierre , Cabassud Corinne
Published: July 2010

Air sparging in membrane filtration consists in generating an intermittent gas/liquid flow by injecting air in the concentrate compartment together with the feed. This process is very efficient for flux enhancement for different membrane processes. In order to understand the influence of wall shear stresses generated by the two‐phase flow on the flux enhancement, this work aimed to characterize local wall shear stresses generated by the two‐phase flow during filtration operated at a low permeate flux. Local wall shear stresses were measured using an electrochemical method in different points of a flat sheet nanofiltration module and for several operating conditions.
Two‐Phase Flow in Porous Media Under Spatially Uniform Magnetic‐Field Gradients
Authors: Iliuta Ion , Larachi Faïçal
Published: July 2010

External inhomogeneous magnetic fields exert a body force on electrically nonconducting, magnetically permeable fluids, and this force can be used to compensate or to amplify the gravitational body force. The ability to influence two‐phase flow by the application of external inhomogeneous magnetic field is of potential interest in the operation of trickle‐bed reactors from the point of view of catalytic process intensification. An exhaustive modeling framework was developed to illustrate how external inhomogeneous magnetic fields are able to influence both trickle bed hydrodynamics and reaction performance. The model was based on the volume‐average mass and momentum balance equations and volume‐average species balance equations under a spatially uniform magnetic‐field gradient, µ20H(dh/dz). The catalytic wet air oxidation of phenol in the presence of a catalyst consisting of a mixture of CuO, ZnO and CoO was considered as a case study.
Modelling of Trickle Bed Reactor for the Catalytic Wet Air Oxidation of Phenol
Authors: Eftaxias Athanasios , Larachi Faiçal , Stüber Frank
Published: July 2010

A non‐isothermal trickle‐bed transport‐reaction model has been developed and tested for the catalytic wet air oxidation of phenol over CuO/γ‐Al2O3. Isothermal simulations confirmed that partial catalyst wetting, and the resulting gas‐solid mass transfer, leads to higher phenol conversions, when oxygen is the limiting reactant. Non‐isothermal simulations evidenced that phenol conversion and adiabatic temperature rise may be overestimated if water evaporation is neglected. When accounting for the latter, the temperature rise exhibited a maximum at gas velocities slightly above the stoichiometric demand for complete mineralisation. It was further observed that under the conditions studied, the temperature rise levels off with increasing inlet phenol concentration, while with increasing inlet temperature it reaches a maximum and then drops.
Experimental Validation of a Two‐Phase Flow Model for Pressure Drop and Liquid Hold‐up in Downflow Packed Bed Bubble Reactors
Authors: Boyer Christophe , Ferschneider Gilles
Published: July 2010

A new model has been developed in order to predict pressure drop and gas fraction of industrial fixed bed reactor operated in downward bubbly flow. The mechanistic approach proposed by Attou and Ferschneider (1999) has been followed. In this approach, mass and momentum balances are solved for gas‐liquid mixture. To solve the system equation, closure laws are needed for the interfacial force between liquid and solid FLS and for the gas fraction expression. These closure laws have been determined by measuring both pressure drop and gas fraction with downward air‐water bubbly flows through a 40 cm diameter fixed bed of glass beads. The averaged gas fraction is measured by using a gamma scanning system that perform attenuation measurements along 64 chords across a section. Finally, a new bubble flow model is proposed to interpret the results.
Hydrodynamic Behavior of a Three‐Phase Spouted Bed with Very Large Particles
Authors: Wang Jinfu , Wang Tiefeng , Liu Lizao , Chen He
Published: July 2010

The hydrodynamic behavior of a three‐phase spouted bed with large particles of diameter 10.5, 12 and 16mm was studied. Liquid circulation was used to spout the large particles. Experiments were carried out to study the influence of the superficial gas velocity, liquid circulation velocity, particle diameter and settled particle bed height on the minimum liquid spouting velocity, pressure drop and gas holdup. In the spouted regime, liquid circulation and the movement of the large particles enhance bubble breakup and increase the gas holdup. The frequent collision of these large particles with the reactor wall and nozzles are helpful in preventing fouling. This indicates a potential application in gas‐liquid systems in which fouling occurs due to deposition and adhesion.
Expanded Bed Column Bioreactor Performance and Hydrodynamics
Authors: Abdul‐Rahman R , Ozaki H , Zainola N
Published: July 2010

Studies on the removal of nitrogen constituents by a dual media expanded bed bioreactor showed substantial removals of about 85% COD and 80% total‐N. Kinetic parameters obtained were: for growth, YH = 0.23mg/mg, µH = 0.278day—1, KH = 461mg/L and bH = 0.0151day—1 and for denitrification, YHD = 0.670mg/mg, µHD = 0.205day—1, KHD = 0.54mg/L and bHD = 0.0300day—1. Hydrodynamics studies gave Ut (terminal settling velocity) and Umf (minimum fluidization velocity) for bare GAC as 0.637m/s and 0.005m/s respectively. For GAC with biofilm, Ut was at 0.426‐0.083m/s, with almost double the increase in buoyancy for particles carrying biofilm. This in turn reduced the Umf for GAC with biofilm, which was at 0.0062‐0.0009m/s.
3D‐ECT Velocimetry for Flow Structure Quantification of Gas‐Liquid‐Solid Fluidized Beds
Authors: Warsito W , Fan Liang‐Shih
Published: July 2010

The electrical capacitance tomography (ECT) velocimetry techniques, namely tomography tracking velocimetry (TTV) and tomography image velocimetry (TIV) are proposed in this study to quantify the flow structure of gas‐liquid‐solid fluidized beds based on the ECT images. The tomography images of the bubbles in the three‐phase system are obtained from image reconstruction using the neural network multi‐criteria optimization image reconstruction technique (NN‐MOIRT), developed earlier by the authors. The TTV is based on an auto‐correlation of tomography images in a single plane sensor to track the three‐dimensional position of a bubble swarm. The TIV is based on a cross‐correlation of tomography images in two plane sensors to calculate the three‐dimensional velocity components of the bubble swarm. The bubble spiral motions, the fluctuations of the three‐dimensional bubble swarm velocity components and fluxes in three‐dimensional space are discussed along with the effect of gas superficial velocity, the presence of solid particles and the column height.
Modeling of an Airlift Reactor with Floating Solids for Wastewater Treatment
Authors: Merchuk José C. , Shechter Ronen
Published: July 2010

This paper presents a three‐phase reactor fluid dynamic model that is used in the development of a generic process for upgrading existing wastewater treatment plants. The core of the process consists of an attached growth airlift reactor (AGAR) in which a biomass carrier is used. Mixing is provided in the aerobic stages by partitions that create an airlift effect. The combination of the organized flow pattern and the low density of the media enables prevention of carrier migration between different process stages, without need of screens. Measurements of liquid velocity in a demonstration plant confirm the predicted values with reasonable accuracy.
The Effect of Bed Temperature on Mass Transfer between the Bubble and Emulsion Phases in a Fluidized Bed
Authors: Wu Wenyuan , Agarwal Pradeep K.
Published: July 2010

The rate of interphase mass transfer between the bubble and emulsion phases of a bubbling fluidized bed is of primary importance in all models for fluidized bed reactors. Many experimental studies have been reported, however, all these investigations have been carried out in fluidized beds operated at room temperature. In this work, the effect of the bed temperature on the interphase mass transfer is reported. Single bubbles containing argon – used as a tracer – were injected into an incipiently fluidized bed maintained at the required temperature. The change in argon concentration in the bubble was measured using a suction probe connected to a mass spectrometer. The effects of bed particle type and size, bubble size, and bed temperature on the mass transfer coefficient were examined experimentally. The interphase mass transfer coefficient was found to decrease with the increase in bed temperature and bubble size, and increase slightly with increase in particle size. Experimental data obtained in this study were compared with some frequently used correlations for estimation of the mass transfer coefficient.
Bitumen Recovery with Oily Air Bubbles
Authors: Wallwork Vince , Xu Zhenghe , Masliyah Jacob
Published: July 2010

Air‐kerosene bubbles were used in a novel laboratory scale pipeline loop to assess the extraction performance of poor processing oil sand ores. The addition of kerosene to air, whereby producing oily bubbles, substantially enhanced bitumen recovery from poor processing oil sand ores. The oily bubbles were added in a pipeline loop during bitumen liberation from the sand grains. The bitumen recovery from poor processing ores with the addition of the oily bubbles to the conditioning slurry becomes comparable to that of good processing ores. The present findings can be of substantial benefit to the oil sands industry.
Enhanced Production of Podophyllotoxin by Fed‐batch Cultivation of Podophyllum hexandrum
Authors: Chattopadhyay Saurabh , Bisaria Virendra S. , Bhojwani Sant S. , Srivastava Ashok Kumar
Published: July 2010

Podophyllum hexandrum (Indian May Apple) was successfully cultivated in a 3 L stirred tank bioreactor under low shear conditions in batch and fed‐batch modes of operation. A statistically optimized culture medium was used for the batch cultivation of Podophyllum hexandrum. Under optimum culture conditions of P. hexandrum, the batch culture showed a growth‐associated product formation with a maximum biomass of 21.4 g/L dry cell weight (DCW) basis and a podophyllotoxin production of 13.8 mg/L in 26 d. A mathematical model was developed to design the nutrient feeding strategies for a fed‐batch cultivation to prolong the productive log phase of cultivation. The fed‐batch cultivation was able to enhance the biomass and podophyllotoxin accumulation to 48 g/L (DCW basis) and 43.2 mg/L, respectively, in 60 d. The volumetric productivity of podophyllotoxin in fed‐batch cultivation was found to be 0.72 mg/(L. d) as opposed to 0.53 mg/(L. d) in batch cultivation under optimized culture conditions.
Extended Linear QDMC of a Gibbsite Crystalliser: A Simulation Study
Authors: Tadayon Abdolsamad , Tadé Moses O. , Ang H. M.
Published: July 2010

An extended linear quadratic dynamic matrix control (EQDMC) of a gibbsite crystallisation system is presented. The process model of the crystalliser is based on the conservation principles of mass and population balances, and kinetic relations including nucleation, growth, and agglomeration correlations. It is shown that the process is non‐linear with constraints and possesses interaction among its process variables. Practical concerns in crysallisation plants such as low flow rates and high magma densities that may lead to solids deposition and eventual line blocking are considered as the system's constraints. The controller is developed by combining extended linear dynamic matrix control (EDMC) and quadratic dynamic matrix control (QDMC) algorithms. Two types of control outputs are considered: controlled and associated variables. The capability of the controller in bringing the controlled variables to their setpoints while maintaining all process constraints within their limits is demonstrated via simulation. It is shown that increasing prediction horizon improves the control performance.
The Tank Drainage Problem Revisited: Do These Equations Actually Work?
Authors: Joye Donald D. , Barrett Branden C.
Published: July 2010

The tank drainage problem with pipeline attached is studied in this work. Laminar and turbulent formulations of this unsteady‐state flow problem are derived and evaluated by experimental data. Additional literature models are also evaluated for comparison. Several experimental configurations were used including a small tank with a vertical tube, the same with various‐ sized orifices, a large tank with a horizontal pipe, and a large tank including a piping system with elbows, vertical drop and horizontal extension. Not all the models performed well under all conditions. Limitations of the models are discussed. The model derived by Loiacono and the model we derived (an exact equivalent) showed the best for both laminar and turbulent flow, predicting drainage times to better than ± 8%, on average.
Slip Flow in Ducts
Authors: Wang Chang Y. I.
Published: July 2010

Slip flow in ducts occurs in many practical fluid transport situations. The method of eigenfunction expansion and collocation is used to solve the velocity distribution for slip flow in ducts of polygonal, elliptic and cuspidal cross sections. The friction factor‐ Reynolds number products are tabulated.
Rheology of Glaze Suspensions
Authors: Savarmand Saeid , Golkar‐Narenji Mohammad‐Reza , Saedi Kourosh
Published: July 2010

Rheological properties of suspensions and ceramic glaze slurries under steady flow conditions have been considered. Colloidal forces play an important role in the rheology of such ceramic slurries. Since the potential function characterizes the rheology of colloidal systems, a new dimensionless group, viz. potential number, is introduced within a dimensional analysis representing the relative significance of the potential to the Brownian energy. In order to relate the relative viscosity to other dimensionless groups, a new model is proposed by the inclusion of an extra term in addition to that of the hard‐sphere theory owing to the fact that the presence of colloidal forces always increases the fluid viscosity with respect to that predicted by the hard‐sphere. Steady viscosity measurements have been carried out on ceramic glaze suspensions at different volume fractions, particle diameters, and shear rates. Experimental results have been used to modify the model relating the relative viscosity to the Péclet number, potential number, volume fraction, and maximum packing fraction.
Gypsum Scale Formation in White Water of a Closed‐Cycled Paper Mill
Authors: Choi Sang‐June , Kim Hae‐Young , Kim Young‐Hun , Park Hyeon , Englezos Peter
Published: July 2010

The accumulation of calcium and sulfate ions in a process stream of a closed papermaking system may cause calcium sulfate scale formation. This study presents measurements of calcium sulfate precipitation conditions and a thermodynamics‐based model for the prediction of such precipitation conditions in the papermaking white water at 50°C. The precipitates were found to have the structure of gypsum (CaSO4·2H2O). The model calculations were compared with experimental data and found to be in good agreement.
Energy Efficiency of an Indirect Thermally Coupled Distillation Sequence
Authors: Hernández Salvador , Pereira‐Pech Salvador , Jiménez Arturo , Rico‐Ramírez Vicente
Published: July 2010

Several thermally coupled distillation sequences have been proposed to improve the thermal inefficiency of conventional distillation sequences. Particularly, for the separation of ternary mixtures, structures that perform a lateral extraction in one of the columns of the integrated arrangement have been shown to provide significant energy savings. The structure of existing sequences, based on conventional distillation columns, might provide the basis for alternate thermally coupled designs. In this paper, it is shown how a thermally coupled system derived from an indirect conventional sequence can provide energy savings through a proper optimization of the interconnecting streams.
Closed‐loop Fault Detection Using the Local Approach
Authors: Cheng Luke L. , Kwok K Ezra , Huang Biao
Published: July 2010

Fault detection and isolation (FDI) has become a crucial issue for industrial process monitoring in order to increase availability, reliability and production safety. Model‐based FDI methods rely on a mathematical model and input‐output data of a process to perform detection. The local approach is a new model‐based FDI method that aims to detect slight changes of a system's parametric properties. Closed‐loop detection is an important issue for the local approach since all control systems work under closed‐loop conditions. A new algorithm was proposed to revise the original detection algorithm in order to make it work for closed‐loop data. Simulation results show that the proposed method can detect the changes of parameters of a system that can affect closed‐loop performance.
Radial Liquid Dispersion and Bubble Distribution in Three‐Phase Circulating Fluidized Beds
Authors: Kang Yong , Cho Yong J. , Lee Chan G. , Song Pyung S. , Kim Sang D.
Published: July 2010

The liquid dispersion and bubble distribution in the radial direction have been investigated in the riser of a three‐phase circulating fluidized bed whose diameter is 0.102m and 3.5m in height. Effects of gas and liquid velocities and solid circulation rate have been determined. It has been found that the radial distribution of bubbles is related closely to the liquid dispersion in the radial direction. The size and rising velocity of bubbles tend to increase as the radial position approaches to the center of the riser. The bubble size increases with increasing UG, but it decreases with increasing UL or GS in all radial positions. The radial dispersion coefficient of the liquid phase increases with increasing UG or GS, however, it tends to decrease with increasing UL. The value of Dr has been well correlated in terms of dimensionless groups based on the isotropic turbulence model.
The Heterogeneous and Homogeneous Combustion of Methane Over Inert Particles
Authors: Sotudeh‐Gharebagh Rahmat , Chaouki Jamal
Published: July 2010

The combustion of methane was studied in a fixed bed reactor to determine the effect of inert particles through heterogeneous and homogeneous reactions. Methane and CO2 mole fractions are measured at the reactor outlet. The results show that any accelerating catalytic effect of the inert particles is quite small, while considerable inhibition effect was found at moderately high temperatures. A plug flow model with a complete and reduced reaction scheme was developed to explain the experimental findings. Both reaction schemes fail to fully predict the experimental data. Therefore, an improved combined mechanism is proposed, which is now able to predict the experimental data.
Catalytic Combustion Kinetics: Using a Direct Search Algorithm to Evaluate Kinetic Parameters from Light‐Off Curves
Authors: Hayes Robert E. , Bertrand François H. , Audet Charles , Kolaczkowski Stan T.
Published: July 2010

This paper describes a method for evaluating the kinetic constants in a rate expression for catalytic combustion applications using experimental light‐off curves. The method uses a transient one‐dimensional single channel monolith finite element reactor model to simulate reactor performance. The heat and mass transfer models used account for developing flow in the entrance region. A parameter global optimization routine based on a generalized pattern Search algorithm is used to determine the best fit parameters in the rate expression for the oxidation of CO and mixtures of CO and CH4. The algorithm is compared to a more classical gradient method, the Fletcher‐Reeves method.
Biodegradation of High Strength Phenolic Wastewater in a Modified External Loop Inversed Fluidized Bed Airlift Bioreactor (EIFBAB)
Authors: Aye Thin Thin , Loh Kai‐Chee
Published: July 2010

An EIFBAB was modified with a mixed‐tank reactor placed in series to extend the phenol treatability range. Phenol degradation at high concentrations was investigated at recycle rates from the mixed‐tank reactor from 0 to 15 L/h under batch operation. With a total working volume of 10 L, the new setup could handle 3000 mg/L phenol at a comparable volumetric biodegradation rate of 9 mg/L·h at optimized operation of 5 L/h recycle rate, as the 11 mg/L‐h in the original EIFBAB. While the original EIFBAB could not handle phenol concentrations exceeding 3000 mg/L, continuous operation was ascertained in the modified EIFBAB for phenol degradation of up to 5000 mg/L phenol and feed flow rates up to 160 mL/h. The recoverability of the system under shock loading of phenol up to 5000 mg/L was also assessed.
A Discussion on Minimum Spout Velocity and Jet Penetration Length
Authors: Bi Hsiaotao T.
Published: July 2010

The similarity and difference between the flat‐bottom and cone‐bottom cylindrical spouted beds, conical spouted beds and vertical upward jets in fluidized beds have been analyzed in this paper based on the effects of geometrical parameters on the minimum spouting velocity and operating stabilities of the spouted beds. The effect of angle on minimum spouting velocity was found to be only significant within the range of 30 to 60 degrees cone angles. Minimum spouting velocity in deep cylindrical spouted beds was proportional to the square root of the static bed height, but was proportional to the static bed height in conical spouted beds and large cylindrical spouted beds with small height‐to‐diameter ratio. The relationship between the minimum spouting velocity and the static bed height was consistent with that between jet velocity and the vertical jet penetration length in jetting fluidized beds.
Validation of a Discrete Particle Model in a 2D Spout‐Fluid Bed Using Non‐Intrusive Optical Measuring Techniques
Authors: Link Jeroen , Zeilstra Christiaan , Deen Niels , Kuipers Hans
Published: July 2010

To gain insight into the hydrodynamics of spout‐fluid beds, an experimental and numerical study was carried out. Particle image velocimetry was successfully developed and applied to determine particle velocity profiles, whereas voidage profiles were determined by digital image analysis. A 3D hard‐sphere discrete particle model was used to simulate the flow in a spout‐fluid bed. The simulations and experiments showed a similar influence of the background fluidization velocity on the spout behaviour.
Analysis of Regime Transitions and Flow Instabilities in Vertical Conveying of Coarse Particles Using Different Solids Feeding Systems
Authors: Costa Ione A. , Do Carmo. Ferreira Maria , Freire José T.
Published: July 2010

The transition between dense and dilute flow in vertical conveying of Geldart D particles were investigated for risers of different diameters using a spouted bed as a solid feeding system. The transition and choking velocities were identified by combining analyses of pressure gradient versus air velocity diagrams, pressure fluctuation signals and voidage values. Experimental data were used to evaluate the effect of particle and riser diameters on the pressure gradient, mean mixture voidage, the regime transition and choking velocities. The transition velocity from dilute to dense phase could be identified, as well as the onset of the choking condition, which appeared as the air velocity was further reduced. Data obtained in the same experimental apparatus facility using a screw conveyor and a gravitational system as solid feeding devices have been used as a reference to be compared to those obtained using the spouted bed feeder.
Identification of Flow Regimes in Slot‐Rectangular Spouted Beds using Pressure Fluctuations
Authors: Freitas Luis A. P. , Dogan Ozkan M. , Lim C. Jim , Grace John R. , Bai Dingrong
Published: July 2010

Pressure fluctuation data recorded in slot‐rectangular spouted beds of 1.44 mm diameter glass beads were analyzed with the aid of statistical and chaotic tools. The column width was maintained at 150 mm, while the thickness and slot width were both varied. It is shown that there are significant shifts in both statistical and chaos measures as the gas flow rate is increased. The results suggest that pressure fluctuations can be used to provide diagnostics of flow regime transitions in spouted beds when viewing is impossible.
Flow Characteristics in Slot‐Rectangular Spouted Beds with Draft Plates
Authors: Luo Baolin , Lim C Jim , Freitas Luis A. P. , Grace John R.
Published: July 2010

An experimental investigation was conducted of slot‐rectangular spouted beds with air entry slots spanning the full thickness of the column and vertical draft plates intended to help control the solids circulation rate. With increasing superficial gas velocity, the flow between the draft plates changed from bubbling to slugging and then to spouting with dilute pneumatic between the plates and moving‐bed downward motion on both sides. However, there was difficulty maintaining stability and symmetrical flow on the two sides. Once spouting is established, pressure drops and local voidages vary with gas velocity, particle size and gas entry size in broadly similar manners as for conventional spouted beds
Influence of Operating Parameters on the Average Spout Width in Two‐Dimensional Spouted Beds
Authors: Zanoelo Éverton F. , Rocha Sandra C. S. , Rezende Daiton F.
Published: July 2010

In this work a set of experiments were performed in a two‐dimensional spouted bed to study the effect of different operating conditions on the spout cavity width. The measurement of spout‐annulus interface along the bed level was made by visual observations on a flat face column. A numerical integration formula was used to calculate the average spout width. The experimental runs were performed with different materials, bed dimensions, static bed heights, fluid velocities and gas inlet orifice width. The influences of these variables on average spout width were verified through a statistical analysis. An empirical correlation is proposed to predict the average spout width. The empirical model parameters were found through a statistical analysis.
Residence Time Distributions in Staged Spouted Beds
Authors: Arriola Enrique , Cruz‐Fierro Carlos Francisco , Alkhaldi Khaled Hamed , Reed Brian Patrick , Jovanovic Goran
Published: July 2010

A novel design of a multi‐staged, continuous flow spouted bed, suitable for counter‐current, cross‐current, and fed‐batch gas‐solid contacting is developed. Single and three‐stage conter‐flow units are studied, the residence time distributions (RTD's) of the solids therein are measured and two compartmental models are developed to fit this family of RTD's. The first (two‐parameter) model is satisfactory for the single stage units, and three‐stage units at high gas flow rates. The second (three‐parameter) model describes each stage as two CSTVs in parallel with a PFV in series. It provides better agreement with experimental data in the three‐stage case.
The Effect of Operating Conditions and Design Parameters on the Dynamic Behaviour of Agitated Pulp Stock Chests
Authors: Ein‐Mozaffari Farhad , Kammer Leonardo C. , Dumont Guy A. , Bennington Chad P. J.
Published: July 2010

Agitated pulp chests provide attenuation of high‐frequency disturbances in pulp properties ahead of many pulping and papermaking unit operations. The effect of process and design variables on the extent of non‐ideal flows was examined in a laboratory‐scale pulp chest. Dynamic tests were made using the frequency‐modulated random binary input of a brine solution with the pulp feed to determine the magnitude of non‐ideal flows (channeling, recirculation and stagnant zones). Results showed that the degree of upset attenuation is a function of impeller momentum flux and fibre mass concentration and that existing design criteria underpredict the power needed to produce a fully mixed system.
Phase Transformation and Rheological Behaviour of Highly Paraffinic “Waxy” Mixtures
Authors: Tiwary Dharmendra , Mehrotra Anil K.
Published: July 2010

An experimental investigation was undertaken for the rheology and phase transformation of prepared solutions comprising a paraffin wax dissolved in n‐dodecane or n‐hexadecane. The liquid‐solid phase transformation in wax‐solvent mixtures was investigated through the measurement of wax appearance/disappearance temperature (using cross polar microscopy, differential scanning calorimetry, viscometry and a visual method), pour point temperature and crystallization temperature. The results were utilized to prepare a temperature‐composition phase diagram for the wax+n‐C16H34 pseudo‐binary system. The effects of composition, temperature, cooling rate and shear rate were studied on the rheology of wax‐solvent mixtures. A correlation was developed for the apparent viscosity of wax‐solvent mixtures.
Isomérisation du n‐hexane sur des catalyseurs Ni‐WOx/Al2O3‐SiO2
Authors: Guemini Miloud , Rezgui Yacine , Bouchemma Ahcene , Tighezza Ammar
Published: July 2010

Isomerization of n‐hexane into bi‐ and tri‐branched products was studied at atmospheric pressure on Ni‐WOx/Al2O3‐SiO2 catalysts. Two groups of catalysts (A and B) were prepared by using the sol‐gel method. The objective of the present study is the selection of the catalyst having the best isomer (bi‐ and tri‐branched) yield under optimum operating conditions (reaction temperature, reduction temperature, flow duration, etc.). The results show that the introduction of tungsten (group B) modifies siginificantly the catalyst activity and that the optimum nickel amount in these catalysts is 15 wt. %. When a steady flow is achieved (100 min), the catalyst containing 15 % nickel and 10 % tungsten exhibits the highest and largest selectivity at a reaction temperature of 250°C and a reduction temperature of 430°C.
Effect of Water on α‐Methylstyrene Hydrogenation on Pd/Al2O3
Authors: Meille Valérie , De Bellefon Claude
Published: July 2010

α‐methylstyrene catalytic hydrogenation on Pd/Al2O3 is frequently used to characterize new reactors. However, whereas many authors report some problems of reproducibility or possible poisoning of the catalyst, no consistent advice is available in the literature to carry out the reaction without these problems. This work points out the inhibition of the reaction by trace amounts of water. An experimental procedure is explained to guarantee the reproducibility of the measures.
Removal of VOCs by Sorption in Fixed Beds of Popcorn
Authors: Mak Vivian W. Y. , Chatzis Ioannis , Hudgins Robert R. , Fayed Muhammad E.
Published: July 2010

Popcorn was the sorbent in a fixed‐bed study on removing VOC contaminants from air. Acetone, toluene, and trichloroethylene were selected as model VOCs to represent industrial solvents with diverse properties. Other variables studied were the inlet VOC concentration and pre‐treatment of the popcorn. Inlet and outlet concentrations were monitored by gas chromatography. The Wheeler equation satisfactorily correlated the breakthrough times of the model VOCs. Because of its low specific surface, popcorn is unlikely to replace activated carbon as a sorbent for VOCs.
Process Design Aspects of Jet Mixers
Authors: Patwardhan Ashwin W. , Thatte Amit R.
Published: July 2010

In the present work, mixing time measurements have been made with jet mixers over a wide range of jet velocities, liquid levels and tank sizes. The nozzle was kept along the axis of the vessel and the nozzle clearance was varied over a wide range. It was observed that the mixing time decreases with an increase in the jet path length (nozzle clearance) for a given tank size and given amount of liquid. The reasons for this behaviour are explained with the help of CFD modelling. The effect of tank diameter has been studied independent of the jet path length. A correlation has been developed for process design. Jet mixers have been compared with impeller‐stirred tanks in terms of their energy efficiency. Reasons for the observed behaviour have been provided.
Turbulence Modulation in Gas‐Particle Flows: A Comparison of Selected Models
Authors: Lightstone Marilyn F. , Hodgson Sarah M.
Published: July 2010

The problem of turbulence modulation, the process whereby the gas‐phase turbulence is modified by the presence of particles, is investigated. Experimental trends are examined and parameters affecting turbulence modulation and the mechanisms by which turbulence modulation occurs are identified. A new model that accounts for the crossing trajectory effect through fluid velocity correlations is presented. This model and the turbulence modulation models of Chen and Wood (1985), Tu and Fletcher (1994), and Mostafa and Mongia (1988) are compared directly to determine inherent differences or similarities of the models. The models are also invoked to simulate a particle‐laden pipe flow and predictions are compared to the experimental results of Tsuji et al. (1984).
Bubble Motion Pattern and Rise Velocity in Two‐dimensional Horizontal and Vertical Vibro‐fluidized Beds
Authors: Zhou Tao , Ogura Hironao , Yamamura Masato , Kage Hiroyuki
Published: July 2010

The motion pattern of a bubble was examined and the bubble rise velocity was measured in horizontally and vertically sinusoidal vibro‐fluidized beds. Experimental results showed that the motion pattern of a bubble depends on the vibration direction. Compared with the case of no vibration, it seems that the flow pattern of bubbles is not affected significantly by vertical vibrations, while bubbles rise in the form of a tower for horizontal vibrations. For vertical vibrations, all the local average bubble rise velocities were larger than those in the case of no vibration, but they were hardly influenced by horizontal vibrations at the lower bed height and were larger than those in the case of no vibration at the higher bed height.
The Two‐Phase Flow in an Axially Stirred Vessel Investigated Using Phase‐Doppler Anemometry
Authors: Ljungqvist Mattias , Rasmuson Anders
Published: July 2010

The phase‐Doppler technique has been used to characterize the two‐phase flow of liquid and particles in a stirred vessel agitated by a pitched blade turbine. The number of measurement locations used is considerably larger than in previous investigations and the behaviour of four different types of particles is studied. The fluid phase and particle phase flow is studied with particular emphasis on the relative velocities of the two phases. The largest slip velocities in the tank were found just beneath the impeller, and large slip velocities generally coincide with large velocity gradients. Generally, particles lag in relation to the fluid when the fluid flow is directed upwards, and vice versa, but exceptions to this are not unusual.
Low Inclination Oil‐water Flows
Authors: Lum Jason Y.‐L. , Lovick Jonathon , Angeli Panagiota
Published: July 2010

Two‐phase liquid flows at +5° inclination from the horizontal were studied experimentally for mixture velocities between 0.7 and 2.5 m/s and input oil fractions between 10% and 90%. The results were compared with a two‐fluid model that includes entrainment. The investigations were performed in a 38‐mm ID stainless steel test section, with water and oil as test fluids. Dual continuous flow (both phases remain continuous with inter‐dispersion) prevailed, while the two‐phase pressure gradient was found lower than the single‐phase oil or water. At low mixture velocities the velocity ratio increased with oil fraction while at high ones it decreased. Compared to horizontal flow, water holdup was higher and frictional pressure gradient lower.
A Composite Heat Transfer Model For Pool Boiling on a Horizontal Tube at Moderate Pressure
Authors: Das Sarit K. , Roetzel Wilfried
Published: July 2010

The present work is aimed at building a comprehensive heat transfer model for pool boiling on horizontal tubes combining sliding bubble mechanism with natural convection, microlayer evaporation and transient conduction during boundary layer reformation, to predict the boiling heat flux for a given wall superheat. The model has been compared to experimental results from literature for R134a and also to independent experiments conducted by the authors for water. Even with a number of simplified assumptions a reasonably good agreement has been observed between model and experiments in the low and medium heat flux region and moderate pressure.