Chemical Engineering & Technology

Cover image for Chemical Engineering & Technology

March, 2004

Volume 27, Issue 3

Pages 195–345

    1. 11th European Conference on Mixing (page 203)

      M. Kraume

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200490006

    2. The Future of Mixing Research (pages 208–214)

      Suzanne M. Kresta, R. Krebs and T. Martin

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200402020

      While the one dimensional problems of mixing are reasonably well understood, current practice actually requires us to address complex, multi-dimensional problems with interactions between mixing, reaction, multi-phase physics, surface phenomena, and transport phenomena. Understanding these multi-scale, multi-physics problems requires models which include interactions between the phenomena, and allow the effects of these interactions to emerge.

    3. State of the Art and Future Trends in CFD Simulation of Stirred Vessel Hydrodynamics (pages 215–224)

      M. Sommerfeld and S. Decker

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200402007

      Computational fluid dynamics has become a widely used tool for analyzing, optimizing, and supporting the design of mixing processes in stirred vessels. The present contribution gives a brief summary of the methods applied for numerically treating the power input by the impeller, such as empirical methods, the multiple frame of reference approach and unsteady methods using sliding or clicking meshes. Thereafter, recent developments and trends in the numerical computation of single phase flows in stirred vessels on the basis of DNS (direct numerical simulations), LES (large eddy simulations), and RANS (Reynolds-averaged Navier-Stokes) approaches are summarised.

    4. Modular Simulation of Fluidized Bed Reactors (Chem. Eng. Technol. 2004, 27, 123). (page 224)

      R. Jafari, R. Sotudeh-Gharebagh and N. Mostoufi

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200490007

    5. CFD Modelling of Mixing Effects on the Course of Parallel Chemical Reactions Carried out in a Stirred Tank (pages 225–231)

      J. Bałdyga and Ł. Makowski

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401992

      Effects of turbulent mixing on the course of two fast parallel chemical reactions (neutralization of sodium hydroxide and hydrolysis of ethyl chloroacetate) carried out in a semibatch stirred tank reactor are experimentally investigated and numerically simulated. The flow pattern in the stirred tank is predicted using CFD and experimentally validated using Laser Doppler Anemometry. Mixing effects are modelled using three CFD based models.

    6. Modeling of Mixing and Precipitation Using CFD and Population Balances (pages 232–236)

      A.R. Paschedag

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401984

      Simulations of particle size distributions in technical precipitation reactors require the consideration of turbulent mixing and precipitation kinetics. For that, spatially resolved population balances have to be evaluated. In turbulent flows these balances cannot be solved directly, instead either Reynolds averaging or Large Eddy Simulations have to be applied while unresolved fluctuations need to be modeled. Reynolds averaging of the population balance leads to a turbulent growth dispersion term which has to be modeled.

    7. CFD Modeling of Turbulent Jacket Heat Transfer in a Rushton Turbine Stirred Vessel (pages 237–242)

      B. Zakrzewska and Z. Jaworski

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401988

      CFD modeling of the turbulent heat transfer was performed for a stirred tank equipped with a Rushton turbine impeller and four standard baffles. Eight different turbulence models were used during the modeling. In all investigated cases, the boundary flow at the vessel wall was described by the standard logarithmic wall functions.

    8. LES Simulation of Jet Mixing Processes With Heat Transfer in Turbulent Pipe Flow (pages 243–248)

      S. Jahnke, N. Kornev, A. Leder and E. Hassel

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401970

      A LES technique is used for investigation of jet mixing processes with heat transfer in a turbulent pipe flow. Predictions were validated for different test problems. Influence of velocity, density, kinematic viscosity, and temperature in a co-flow and in an admixture as well as the effect of the Reynolds number on mixing were studied. Two efficient methods of mixing control, namely periodic injection and swirling jets, were investigated.

    9. Particle Flow Modelling in Slurry-Fed Stirred Vessels (pages 249–256)

      F. Scargiali, F. Grisafi, J. Cermakova, V. Machon and A. Brucato

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200402008

      Experimental data on particle Residence Time Distribution (RTD) in a high-aspect-ratio vessel stirred by three equally-spaced Rushton turbines, obtained by means of Twin Systems Approach (TSA), are employed to assess the suitability of the well known Axial-Dispersion Model to describe particle behavior in the investigated system. The data analysis and model parameter assessment are preceded by a discussion on the utility of self-recirculated systems in carrying out experiments concerning continuous slurry-fed apparatuses.

    10. Large Eddy Simulation of Turbulent Flow in a Rushton Impeller Stirred Reactor with Sliding-Deforming Mesh Methodology (pages 257–263)

      S.L. Yeoh, G. Papadakis, K.C. Lee and M. Yianneskis

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401994

      Mixing operations form a substantial part of the total process industry costs for the manufacture of chemicals, polymers, etc. It is therefore essential that simulation techniques be developed which can provide reliable data, alleviate the need for extensive and expensive experimentation, and facilitate rapid design changes and optimization of stirred processes.

    11. A Multi-Block Approach to Obtain Angle-Resolved PIV Measurements of the Mean Flow and Turbulence Fields in a Stirred Vessel (pages 264–269)

      F.R. Khan, C.D. Rielly and G.K. Hargrave

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401998

      Two-dimensional Particle Image Velocimetry (PIV) measurements have been used to characterize the complex turbulent flow in a fully turbulent stirred vessel. To maintain high spatial resolution when viewing the whole vessel, a multi-block approach has been developed, which combines data from different fields of view into a composite flow map. Angle-resolved mean velocity maps and turbulence properties, have been estimated near to the blade, as well as in the bulk of the vessel, at a spatial resolution.

    12. Hydrodynamics in a Stirred Square Tank Investigated Using a 3-D PIV LES Decomposition Approach and LDA Measurements (pages 270–274)

      J. Kilander and A. Rasmuson

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401983

      The hydrodynamics and turbulence in a square tank stirred with the hydrofoil impeller Lightnin A310 is investigated using a large eddy particle image velocimetry approach. Particle image velocimetry data are used, as the large scale part of a large eddy simulation and the small scales are modelled by direct calculation of the turbulent stress tensor using filtered particle image velocimetry data. The macro instabilities of the flow structure were investigated by means of spectral analysis. Low frequency phenomena separated from the mean flow were detected.

    13. Determination of Dissipation Rate in Stirred Vessels Through Direct Measurement of Fluctuating Velocity Gradients (pages 275–281)

      S. Baldi, A. Ducci and M. Yianneskis

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401979

      2-D and 3-D PIV and 4-channel LDA techniques were employed to measure the turbulence energy dissipation rate in vessels stirred by Rushton impellers. The impellers were rotated at speeds corresponding to Reynolds number of 40,000 to ensure fully-turbulent flow in the vessels. The kinetic energy dissipation rate was determined directly from measurements of the Reynolds stress gradients by analyzing the PIV images over interrogation areas down to 0.1 mm.

    14. Design of Horizontal Vessels Operated as CSTR – Basic Mixing Tasks, RTD, Productivity (pages 282–286)

      P. Forschner, D. Houlton, V. Kassera, R. Klepper and R. Krebs

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401990

      Agitator performance in standard vertical vessels with cylindrical shape, dished bottom, and zero to four baffles has been the topic of numerous publications. In certain industries, however, horizontal cylindrical vessels with hemispherical ends, divided internally into multiple compartments, are preferred for continuous processes operating at high pressures. Use of standard correlations derived from vertical vessels may lead to incorrect performance predictions for these horizontal vessels, and hence unsatisfactory process results.

    15. Macro- and Micromixing in a Taylor-Couette Reactor with Axial Flow and their Influence on the Precipitation of Barium Sulfate (pages 287–292)

      B. Judat, A. Racina and M. Kind

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401997

      A new set-up for precipitation experiments capable of independent adjustment of micro- and macromixing conditions is presented. The setup consists of a Taylor-Couette reactor serving as the reaction zone and an external loop where the slower stages of precipitation processes take place. Micromixing has been investigated with a chemical reaction system and with PIV-measurements.

    16. Mixing in Sub-micron Ducts (pages 293–296)

      E.B. Nauman and A. Nigam

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401991

      Typical current applications of microfluidics have device sizes of 10 to 100 micron, this is sufficiently small to force laminar flow but not so small that molecular diffusion is a dominant factor. In the smaller devices contemplated here, diffusion is important and existing mixing strategies and correlations are no longer applicable. Novel results and interesting complexities are discussed for reactive, single and two phase flows in sub-micron channels.

    17. The Mixing Efficiency of an Eccentric-Disc Kneading Zone in Intermeshing Co- and Counter-Rotating Twin-Screw Extruders (pages 297–303)

      H. Brod and U. Liesenfelder

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200402001

      The distributive mixing efficiency of a twin-screw extruder kneading zone consisting of eccentric disc elements was measured using an online video technique. Both co- and counter-rotation were examined. Viscous Newtonian silicone oil was used as model liquid and black iron oxide pigment served as tracer substance. The energetic efficiency of the mixers investigated is compared by applying the concept of specific action.

    18. Gas Flow Behavior in a Two-Phase Reactor Stirred with Triple Turbines (pages 304–309)

      H. Majirova, D. Pinelli, V. Machon and F. Magelli

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401989

      In a gas-liquid reactor stirred with triple pitched blade turbines the gas behavior of coalescing (water) and non-coalescing (sodium sulphate solution) systems were investigated. The gas phase behavior was characterised by means of the RTD. The axial dispersion model describes the experimental data for water well and satisfactorily for the coalescence-inhibiting solutions. The influence of the operating conditions, the turbine type, and the system coalescing behavior on the model parameter is discussed. A comparison is made to similar data regarding Rushton turbines and high-solidity ratio hydrofoils, as well as gas hold-ups.

    19. Mixing Studies Related to the Cleaning of Molten Aluminium (pages 310–314)

      M. Kimata, N. Nayan, W. Bujalski, Alvin W. Nienow, J.L. Song and M.R. Jolly

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401982

      Molten aluminium is traditionally “cleaned” by a chlorine-based fluxing gas. This gas also has to provide the motive power for mixing. Recently, mechanical agitation with solid fluxes has been considered as a replacement for environmental reasons. Here, these two methods of mixing are compared using particle image velocimetry (PIV), decolourisation for homogenisation, and power measurement for comparison of efficiencies.

    20. Effects of Fine Scale Turbulent Flow and Mixing in Agglomerative Precipitation (pages 315–323)

      J. Bałdyga, M. Jasińska, A. Krasiński and A. Rožeń

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401993

      Precipitation of a solid product from aqueous ionic solutions is considered. This work concentrates on the phenomenon of particle agglomeration that dominates the precipitation process at high supersaturation. Modeling is performed for particles of equal and unequal size. The concept of probability of agglomeration based on multifractal formalism is introduced and applied. A simplified version of the model is linked to CFD and results of computations are compared with experimental data for barium sulfate precipitation.

    21. Coaxial Mixer Hydrodynamics with Newtonian and non-Newtonian Fluids (pages 324–329)

      S. Foucault, G. Ascanio and P.A. Tanguy

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401996

      The performance of several combinations of counter-rotating and co-rotating dispersing impellers in a coaxial mixer operated in counter- and co-rotating mode were assessed with Newtonian and non-Newtonian fluids. The hybrid impeller-anchor combination was found to be the most efficient for mixing in counter-rotating or co-rotating mode regardless of the fluid rheology. The determination of the minimum agitation conditions to achieve the just suspended state of solid particles was also determined.

    22. Influence of Physical Properties on Drop Size Distribution of Stirred Liquid-Liquid Dispersions (pages 330–334)

      M. Kraume, A. Gäbler and K. Schulze

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200402006

      An experimental investigation was carried out to analyse the influence of coalescence behaviour on drop size distributions in stirred liquid-liquid dispersions. An endoscope measurement technique allows the determination of drop sizes even with high volumetric dispersed phase fractions of up to 0.5. The influence of pH and addition of ions was studied by shaking and stirring experiments. Results for high and low coalescence rates are discussed.

    23. LDA-Measurements in a Stirred Tank With a Liquid-Liquid System at High Volume Percentage Dispersed Phase (pages 335–339)

      F.J.E. Svensson and A. Rasmuson

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401981

      The purpose of this study is to evaluate how the flow is influenced by the volume percentage of dispersed phase in a liquid-liquid system. A novel model system consisting of two refraction index matched immiscible liquids is presented along with experimental velocity vector fields of the continuous phase that utilises the non-intrusive Laser-Doppler-Anemometry technique.

    24. Steering of Liquid Mixing Speed in Interdigital Micro Mixers – From Very Fast to Deliberately Slow Mixing (pages 340–345)

      P. Löb, Klaus S. Drese, V. Hessel, S. Hardt, C. Hofmann, H. Löwe, R. Schenk, F. Schönfeld and B. Werner

      Version of Record online: 26 FEB 2004 | DOI: 10.1002/ceat.200401995

      Very fast mixing in the range of milliseconds as well as deliberately slow mixing was realized by specially adjusted interdigital micro mixers made of glass or stainless steel. The corresponding micro mixers are presented including experimental and theoretical investigations of the respective mixing process. Fast mixing was realized by combination of flow multilamination by interdigital microstructured feeding structures with geometric focusing. Details on the microfabrication, achievable throughputs, and hydrodynamics are discussed. To prevent clogging of microsized feeding structures in the case of precipitation reactions, mixing was deliberately slowed down by separating the reactant solutions at the outlet by additional layers of inert liquids.