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  • 1.
    Alexiadis, Alessio
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Dudukovic, M. P.
    Ramachandran, P.
    Cornell, Ann
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Wanngard, J.
    Bokkers, A.
    Liquid-gas flow patterns in a narrow electrochemical channel2011In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 66, no 10, p. 2252-2260Article in journal (Refereed)
    Abstract [en]

    The flow in a narrow (3 mm wide) vertical gap of an electrochemical cell with gas evolution at one electrode is modeled by means of the two-phase Euler-Euler model. The results indicate that at certain conditions an unsteady type of flow with vortices and recirculation regions can occur. Such flow pattern has been observed experimentally, but not reported in previous modeling studies. Further analysis establishes that the presence of a sufficient amount of small (similar to 10 mu m) bubbles is the main factor causing this type of flow at high current densities.

  • 2.
    Alvfors, Per
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Svedberg, Gunnar
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Modelling of the simultaneous calcination, sintering and sulphation of limestone and dolomite1992In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 47, no 8, p. 1903-1912Article in journal (Refereed)
    Abstract [en]

    The partially sintered spheres model, describing the sulphation of a sorbent particle consisting of CaO and inert content, is incorporated in a model taking into account the calcination of the limestone or dolomite and the sintering of the nascent oxide resulting from the calcination. The model is applicable, for example, to the sulphation of limestone or dolomite when injected into the furnace of a pulverized coal-fired boiler. The simulations show a temperature optimum in the calcium conversion. Increased calcium conversion is found when inert material is present. Satisfactory experimental verifications of the model are shown.

  • 3.
    Alvfors, Per
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Svedberg, Gunnar
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Modelling of the sulphation of calcined limestone and dolomite—a gas-solid reaction with structural changes in the presence of inert solids1988In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 43, no 5, p. 1183-1193Article in journal (Refereed)
    Abstract [en]

    The partially sintered spheres model is further developed to account for the influence of inert material present in the solid reactant. This model is applicable, for example, to the sulphation of CaO with a variable amount of inert material. An example is the reaction between calcined dolomite, CaO·MgO, and SO2, when used as an SO2 sorbent in a boiler furnace. The results show that the rate of reaction increases and the active part of the sorbent reaches a higher degree of conversion when inert material is present.

  • 4.
    Bergström, Jonas
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Poggendorf, Stefanie
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Vomhoff, Hannes
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Measurement of the radial velocity in a cylindrical through-flow hydrocyclone2006In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405Article in journal (Other academic)
  • 5.
    Birgersson, Henrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Birgersson, E
    Boutonnet, Magali
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    Mathematical Analysis of Thermally Oxy-Chlorine Regenerated Three-Way CatalystsIn: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405Article in journal (Refereed)
  • 6.
    Chen, Chao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing.
    Jonsson, Lage
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy. FOI, Swedish Defence Research Agency, Division of CBRN Defence and Security.
    Tilliander, Anders
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Cheng, Guoguang
    State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    A Mathematical Modeling Study of the Influence of Small Amounts of KCl Solution Tracers on Mixing in Water and its Residence Time Distribution in a Continuous Flow Reactor-Metallurgical Tundish2015In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 137, p. 914-937Article in journal (Other academic)
    Abstract [en]

    In an earlier research (Chen et al., 2015a) a mathematical model was established to simulate tracer mixing (a KCl solution). The predicted Residence Time Distribution (RTD) curves showed good agreements with experimental RID curves for larger amounts of tracer additions. However, for smaller additions (50 mL) of a KCl solution into water, the predicted RID curves tended to deviate from the experimental RTD curves for a tundish (a continuous flow reactor). The current paper focuses on the possibilities that the predictability for smaller additions could be resolved by using a suitable turbulence model. The performance of five different turbulence models representing different modeling techniques and levels of complexity were tested in combination with using a density-coupled mixed composition fluid model to simulate the mixing, i.e. the following models: LVEL, Chen-Kim k-epsilon, MMK k-epsilon, Explicit Algebraic Reynolds Stress Model (EARSM), and Large Eddy Simulation (LES): Wall-Adapting Local Eddy-viscosity (WALE). The results indicate that models that tend to resolve turbulence structures renders better predictions of the mixing process of smaller tracer amounts. In addition, the influence of different tracer amounts on the flow in tundish was assessed. The simulation results for 75 mL, 100 mL, 150 mL, and 250 mL KCl tracer additions were compared. The results showed that in an upward flow the tracer will, sooner or later (dependent on the tracer amount), sink to the bottom. This is due to the higher density of the tracer compared to the density of water. From a physical modeling perspective, this issue is like the "butterfly effect". It is showed that for a slight increase of the amount of tracer, the flow field might be disturbed. This, in turn, will result in a shifted RTD curve.

  • 7.
    Edsberg, Lennart
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Design and characterisation of a close-concentric annular reactor for kinetic studies at high temperatures2002In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 57, no 5, p. 749-762Article in journal (Refereed)
    Abstract [en]

    A novel annular reactor for kinetic studies at high temperature and flow conditions has been designed to keep eccentricity tolerances below 10%. In a previous work, we have shown that it is very important to keep such low eccentricity values in order to collect reliable kinetic data from this type of reactors. As proposed in this study, a modified reactor with the use of a spacer could guarantee an annular duct with low levels of eccentricity. Manufacturing tolerances or deformation effects giving rise to eccentricity can be significantly minimised when using this apparatus. The reactor has been both experimentally and theoretically characterised. Carbon monoxide oxidation was used as a model reaction under mass-transfer limited conditions revealing an eccentricity of similar to5%. With such small eccentricity levels, a concentric annular form can be assumed in the reactor analysis. Simple 1D or 2D models can therefore be inexpensively used in the evaluation of the kinetic data. Also, prior to the design of the annular reactor, a numerical investigation was carried out to clarify the effects of eccentricity, physical properties of the carrier gas and the annular aspect ratio on mass-transfer limitations. Contrary to expectations, a considerable increase in the fuel mass-diffusivity by carrier gas substitution did not change the mass-transfer rates for cases when eccentricity and aspect ratios were high.

  • 8.
    Edsberg, Lennart
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Effect of eccentricity and interaction between kinetics and mass transfer on the behaviour of catalytic annular reactors: a comparison between lumped and distributed models2001In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 56, no 16, p. 4863-4878Article in journal (Refereed)
    Abstract [en]

    A numerical investigation has been carried out on an isothermal annular reactor for kinetic studies under laminar flow conditions. The scope was to investigate the effects of eccentricity in the annular reactor and the adequacy of using lumped models when modelling such cases. ID-models were compared with the corresponding 3D-models for different values of eccentricities and for different kinetic rate laws. In the case of linear kinetics, the solutions of the lumped models agreed satisfactorily with the solutions of the distributed models for all eccentricity values investigated. However, for non-linear kinetics, especially for LHHW rate expressions, significant differences in conversion between the models were observed during a mixed chemical diffusion-control regime. The differences became progressively larger as the eccentricity was increased. An enhanced ID-model, with compensation for those non-linear effects, was designed and gave satisfactory agreement with the 3D-models. For conditions when the ID-model could predict multiple steady states, a higher eccentricity produced a wider temperature range over which multiplicity occurred. This was so even in the cases where the multidimensional models did not predict any multiple steady states. It is not in general possible to rely on evaluating kinetic data from an eccentric annular reactor by using a ID-model. In order to be sure to obtain accurate data from this type of reactor, an eccentricity of less than 10% is allowed.

  • 9.
    Edsberg, Lennart
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Simplified method for effectiveness factor calculations in irregular geometries of washcoats2000In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 55, no 8, p. 1447-1459Article in journal (Refereed)
    Abstract [en]

    A simplified method to calculate the effectiveness factors in irregular geometries of washcoats is presented. The method is based on sectioning the washcoat into particles and treating each particle in a 1D approach. This simplified method was compared with a rigorous 2D model for different kinds of geometrical shapes and kinetic expressions of the washcoat. For a first- and 0.75th-order reaction, the simplified method showed a good agreement with the 2D model. For a Langmuir-Hinshelwood rate expression, giving effectiveness factors higher than one, the simplified method could give rise to errors up to 14% due to inhibition effects. However, this was only significant at intermediate Values of temperatures and high surface concentrations on the washcoat. In general, the simplified method gives a good a priori estimation of the effectiveness factor that can replace tedious and time-consuming finite element calculations in irregular shapes of washcoats. A comparison of the CPU-time required to solve a 2D-reactor model has been conducted for the different approaches to evaluate the effectiveness factor.

  • 10.
    Eriksson, Sara
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Schneider, A.
    Mantzaras, J.
    Wolf, M.
    Järås, Sven
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Experimental and numerical investigation of supported rhodium catalysts for partial oxidation of methane in exhaust gas diluted reaction mixtures2007In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 62, no 15, p. 3991-4011Article in journal (Refereed)
    Abstract [en]

    The partial oxidation of methane/oxygen mixtures with large exhaust gas dilution (46.3 vol% H2O and 23.1 vol% CO2) has been investigated experimentally and numerically over Rh/CeO2-ZrO2, Rh/ZrO2 and Rh/alpha-Al2O3 catalysts. Experiments were carried out in a short-contact-time (similar to 8 ms) reactor at 5 bar and included exhaust gas analysis, temperature measurements along the reactor, and catalyst characterization. Additional experiments were performed in an optically accessible channel-flow reactor and involved in situ Raman measurements of major gas-phase species concentrations over the catalyst boundary layer and laser-induced fluorescence (LIF) of formaldehyde. A full elliptic two-dimensional numerical code that included elementary hetero-/homogeneous chemical reaction schemes and relevant heat transfer mechanisms in the solid was used in the simulations. The employed heterogeneous reaction mechanism, including only active Rh sites, reproduced the experiments with good accuracy. The ratio of active to geometrical surface area, deduced from hydrogen chemisorption measurements, was the single model parameter needed to account for the effect of different supports. This indicated that water activation occurring on support sites, resulting in inverse OH spillover from the support to the noble metal sites, could be neglected under the present conditions with high water dilution. An evident relationship between noble metal dispersion and catalytic behavior, in terms of methane conversion and synthesis gas yields, could be established. Both measurements and predictions indicated that an increasing Rh dispersion (in the order Rh/alpha-Al2O3, Rh/ZrO2, and Rh/CeO2-ZrO2) resulted in higher methane conversions, lower surface temperatures, and higher synthesis gas yields.

  • 11. Granberg, R. A.
    et al.
    Ducreux, C.
    Gracin, S.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Primary nucleation of paracetamol in acetone-water mixtures2001In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 56, no 7, p. 2305-2313Article in journal (Refereed)
    Abstract [en]

    The influence of solvent composition on primary nucleation of 4-hydroxyacetanilide (paracetamol) in acetone-water mixtures is investigated. The induction time for primary nucleation is determined, at various degrees of supersaturation and at different temperatures, in different solvent mixture compositions. Supersaturation is generated by the addition of water. and the homogeneous, agitated, isothermal solution is allowed to nucleate. The supersaturation driving force is calculated as the difference in the chemical potential. At equal thermodynamic driving force, the induction time depends on the composition of the solvent mixture. The interfacial energy is in the range 1-3 mJ/m(2) and tends to increase with decreasing solubility, i.e. increasing water content. The interfacial energy is slightly lower than a value calculated from a contact angle measurement (5 mJ/m(2)) in pure water and is significantly lower than values predicted by equations derived From simplified theories.

  • 12. Guillard, F.
    et al.
    Tragardh, C.
    Fuchs, Laszlo
    A study on the instability of coherent mixing structures in a continuously stirred tank2000In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 55, no 23, p. 5657-5670Article in journal (Refereed)
    Abstract [en]

    Mixing of an inert marker added to the bulk region of a Rushton-turbine-agitated reactor was investigated by planar laser-induced fluorescence. The effect of the turbine agitation speed on the mixing process was initially studied statistically. Average concentration fields, calculated at several sections of the reactor, revealed the general spreading of the contaminant. This approach, however, was found to be unsatisfactory in studying the mechanisms of macro-mixing in the reactor because of the strong intermittence in the flow. Therefore, the concentration data were analysed using conditional techniques, namely the dynamic structural concept, so as to identify the presence of coherent mixing structures and characterise them in space. Instability patterns were observed with increasing turbine agitation speed from 0.3 to 0.7 W/m(3). Using geometrical concepts, the mechanisms of this spatial instability were further described. General conclusions on the spreading of the contaminant were drawn on the basis of the how instability with respect to transport by convection and diffusion phenomena.

  • 13.
    Kekesi, Timea
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Drop deformation and breakup in flows with shear2016In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 140, p. 319-329Article in journal (Refereed)
    Abstract [en]

    A Volume of Fluid (VOF) method is applied to study the deformation and breakup of a single liquid drop in shear flows superimposed on uniform flow. The effect of shearing on the breakup mechanism is investigated as a function of the shear rate. Sequential images are compared for the parameter range studied; density ratios of liquid to gas of 20, 40, and 80, viscosity ratios in the range 0.5-50, Reynolds numbers between 20, a constant Weber number of 20, and the non-dimensional shear rate of the flow G = 0-2.1875. It is found that while shear breakup remains similar for all values of shear rate considered, other breakup modes observed for uniform flows are remarkably modified with increasing shear rate. The time required for breakup is significantly decreased in strong shear flows. A simple model predicting the breakup time as a function of the shear rate and the breakup time observed in uniform flows is suggested.

  • 14. Lindberg, M.
    et al.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Reaction crystallization in strained fluid films2001In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 56, no 10, p. 3257-3273Article in journal (Refereed)
    Abstract [en]

    The detailed conditions during the ultimate stage of micromixing of the reactants in a reaction crystallization process are analysed. A mathematical model is developed to describe mass transfer, chemical reaction, and crystallization of a molecular compound in strained lamellar structures of reactant solutions inside the smallest vortices. The numerical calculations show that the supersaturation varies significantly in space and time, and suggest that significant crystallization may occur inside these vortices in the case of low-soluble and sparingly soluble compounds. At the end of the vortex lifetime, the crystal size distribution is quite dependent on the properties of the system and on the processing conditions. The number of crystals generated correlates strongly to the maximum supersaturation occurring during the vortex lifetime, and this maximum supersaturation is as a first approximation well described by simplified mass transfer models where crystallization is neglected. Often a significant supersaturation remains at the end of the vortex lifetime and the size of the crystals leaving the vortex is determined by the growth rate rather than by nucleation and mass constraint. The mean size is usually larger than the limiting size for Ostvald ripening in the bulk and the size distribution is quite narrow. The results show that neglect of the detailed conditions in reaction crystallization of a molecular compound may not be justified.

  • 15. Lindberg, M.
    et al.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Supersaturation generation at the feed point in reaction crystallization of a molecular compound2000In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 55, no 10, p. 1735-1746Article in journal (Refereed)
    Abstract [en]

    The maximum product concentration of a molecular compound at the feed point in reaction crystallization is analysed by modelling. A model describing unsteady mass transfer and chemical reaction in strained, semi-infinite, fluid films is combined with models describing productivity constraints and reactant concentration changes during the course of a process. The maximum product concentration is taken as a first estimate of the maximum supersaturation and is used as a basis to discuss the product crystal size that may be produced. The result suggests that at certain conditions we may find smaller product crystals at decreased reactant concentrations. The maximum concentration varies during the course of a single-feed semibatch process and the highest value is not necessarily found in the beginning. The variation with time, depends on the choice of the reactant to feed, and the results provide an explanation to why the product crystal mean size may depend on the choice of feed reactant. Guidelines are proposed for how to decide on optimum reactant solution concentrations and for how to select the reactant to feed in a semibatch process. In addition it is suggested that larger crystals may be produced if the feed reactant concentration is low early in the process and is allowed to gradually increase with time in a controlled way. The term programmed feed concentration'' is introduced.

  • 16.
    Luna, Fabio
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Martínez, Joaquín
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Stability Analysis in Multicomponent Drying of Homogeneous Liquid Mixtures1999In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 54, no 24, p. 5823-5837Article in journal (Refereed)
    Abstract [en]

    A stability analysis of the ordinary differential equations describing the process of convective gas-phase-controlled evaporation during drying is performed. Isothermal and non-isothermal as well as batch and continuous drying processes are considered. For isothermal evaporation of a ternary mixture into pure gas, the solutions of the differential equations are trajectories in the phase plane represented by a triangular diagram of compositions. The predicted ternary dynamic azeotropic points are unstable or saddle. On the other hand, binary azeotropes are stable when the combination of the selectivities of the corresponding components is negative. In addition, pure component singular points are stable when they are contained within their respective isolated negative selectivity zones. Under non-isothermal conditions, stable azeotropes are characterized by presenting maximum temperature values. Loading the gas with one or more of the components up to some value leads to a node-saddle bifurcation, where a saddle azeotrope and a stable azeotrope coalesce and disappear. The continuous drying process yields similar results for both flat and annular geometries. The singular points, in this case, are infinite and represent dynamic equilibrium points whose stability is mainly dependent on the inlet gas-to-liquid flowrate ratio. As this ratio grows to infinity, the phase portrait changes and the process approaches a batch behaviour so that the stability analysis for that case may be applied. The present stability analysis permits the prediction of trajectories and final state of a system in a gas-phase-controlled drying process.

  • 17.
    Martinez, Joaquin
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Rodriguez Varela, Raquel
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Forsberg, Kerstin
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Resource recovery.
    Rasmuson, Åke C.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Factors Influencing Separation Selectivity of Rare Earth Elements in Flat Sheet Supported Liquid Membranes2018In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 191, p. 134-155Article in journal (Refereed)
    Abstract [en]

    Separation selectivity of the mixture Yttrium-Neodymium-Dysprosium using Bis (2-ethylhexyl) hydrogen phosphate (D2EHPA) as extractant in a flat sheet supported liquid membrane was studied by simulations. A new definition of selectivity and a diffusional-kinetic transient model were used in the calculations. Resistance distribution between the phases, stripping phase pH, extractant concentration and initial feed concentration have great influence on selectivity and process time and their appropriate management would improve separation. The analysis of selectivity using the present model would be a useful tool to design a multistage process aimed at the separation of a multicomponent mixture of rare earth elements into its constituents.

  • 18.
    Martínez, Joaquín
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Setterwall, Fredrik
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Gas-phase controlled convective drying of solids wetted with multicomponent liquid mixtures1991In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 46, no 9, p. 2235-2252Article in journal (Refereed)
    Abstract [en]

    The nonisothermal convective drying of an impermeable solid substrate covered with multicomponent solvent mixtures was studied. The aim was to simulate the nonsteady-state evaporation process under the control of the gas side heat and mass transfer. Diffusional resistances in the liquid layer were prevented by choosing conditions providing low evaporation rates. Evaporation fluxes were calculated by assuming either interactive or independent diffusion through the gaseous boundary layer. The interactive effects were accounted for by applying the linearized theory of Toor. Independent fluxes were calculated using the effective diffusivity method. In the experimental part, a Teflon substrate wetted with the binary mixture acetone—methanol, the ternary mixture ethanol—methylethylketone—toluene and the quaternary mixture ethanol—methanol—acetone—chloroform was dried using air flowing parallel to the evaporation surface as drying agent. Good agreement was obtained between experiments and simulations. Calculations show that liquid composition, liquid temperature, gas composition and diffusional interactions have a significant influence on the instantaneous selectivity while the effect of gas temperature and gas velocity is less important. Selectivity can be controlled by using a gas preloaded with an appropriate composition. The model can be applied to the drying, at an initial stage, of coated laminates with a gentle drying regime.

  • 19. Mattsson, Tuve
    et al.
    Sedin, Maria
    Theliander, Hans
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Zeta-potential and local filtration properties: Constitutive relationships for TiO(2) from experimental filtration measurements2011In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 66, no 20, p. 4573-4581Article in journal (Refereed)
    Abstract [en]

    The use of filtration to separate solid from liquids is a commonly-used unit operation employed in a range of different applications. The development of accurate models is therefore important in facilitating e.g. design, scale-up and troubleshooting. Accurate constitutive relationships between local filtration properties need to be formulated in order to form precise models of the filtration process. One important parameter that is seldom considered explicitly in filtration models is the inter particle forces, e. g. electrostatic forces. The aim of this study is to investigate local filtration properties, under controlled conditions, for the model material TiO(2) where the zeta-potential, and thereby one important parameter affecting the inter-particle interactions, is altered. In this study the local solidosity is measured during filtration by gamma-attenuation, the local pressure is measured using capillary tubes. These data are used to calculate the local specific filtration resistance. The compressibility of the filtration cake was changed substantially by altering the zeta-potential. Several published constitutive relationships between local data and specific filtration resistance were applied; they yielded very similar parameters that were in good accordance with the characterization of the material.

  • 20.
    Niskanen, Ilpo
    et al.
    Univ Oulu, Fac Technol Struct & Construct Technol, POB 7300, FI-90014 Oulu, Finland. iskanen, Ilpo; Zakrisson, Daniel; Reza, Salim; Fedorov, Igor; Thungstrom, Goran.
    Forsberg, Viviane
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. Mid Sweden Univ, Dept Nat Sci, Holmgatan 10, SE-85170 Sundsvall, Sweden.
    Zakrisson, Daniel
    Reza, Salim
    Hummmelgård, Magnus
    Andres, Britta
    Federov, Igor
    Suopajärvi, Terhi
    Liimatainen, Henrikki
    Thungström, Göran
    Determination of nanoparticle size using Rayleigh approximation and Mie theory2019In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 201, p. 222-229Article in journal (Refereed)
    Abstract [en]

    Accurate determination of the size of nanoparticles has an important role in many different scientific and industrial purposes, such as in material, medical and environment sciences, colloidal chemistry and astrophysics. We describe an effective optical method to determine the size of nanoparticles by analysis of transmission and scattering of visible spectral range data from a designed UV-Vis multi-spectrophotometer. The size of the nanoparticles was calculated from the extinction cross section of the particles using Rayleigh approximation and Mie theory. We validated the method using polystyrene nanospheres, cellulose nanofibrils, and cellulose nanocrystals. A good agreement was achieved through graphical analysis between measured extinction cross section values and theoretical Rayleigh approximation and Mie theory predictions for the sizes of polystyrene nanospheres at wavelength range 450-750 nm. Provided that Rayleigh approximation's forward scattering (FS)/back scattering (BS) ratio was smaller than 1.3 and Mie theory's FS/BS ratio was smaller than 1.8. A good fit for the hydrodynamic diameter of nanocellulose was achieved using the Mie theory and Rayleigh approximation. However, due to the high aspect ratio of nanocellulose, the obtained results do not directly reflect the actual cross-sectional diameters of the nanocellulose. Overall, the method is a fast, relatively easy, and simple technique to determine the size of a particle by a spectrophotometer. Consequently, the method can be utilized for example in production and quality control purposes as well as for research and development applications.

  • 21.
    Rodrigues, Diogo
    et al.
    Laboratoire d'Automatique, EPFL, Lausanne, CH-1015, Switzerland.
    Billeter, J.
    Bonvin, D.
    Generalization of the concept of extents to distributed reaction systems2017In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 171, p. 558-575Article in journal (Refereed)
    Abstract [en]

    In the chemical industry, a large class of processes involving reactions can be described by partial differential equations that depend on time and on one or more spatial coordinates. Examples of such distributed reaction systems are tubular reactors and reactive separation columns. As in lumped reaction systems, the interaction between the different rate processes (reactions, mass and heat transfers, and inlet and outlet flows) complicates the analysis and operation of distributed reaction systems. In this article, the concept of extents, which has been applied to decouple the rate processes in lumped reaction systems with one or multiple phases, is generalized to distributed reaction systems. Both the concept of extents and a linear transformation to extents are detailed for various configurations of tubular reactors and reactive separation columns, as well as for a more generic framework that is independent of the configuration and operating conditions. The application of extents to distributed reaction systems is illustrated through several case studies that show how the effect of each rate process can be expressed in terms of a corresponding extent.

  • 22.
    Rodrigues, Diogo
    et al.
    Laboratoire d'Automatique, EPFL, Lausanne, CH-1015, Switzerland.
    Billeter, J.
    Bonvin, D.
    Semi-analytical solutions for tubular chemical reactors2017In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 172, p. 239-249Article in journal (Refereed)
    Abstract [en]

    The one-dimensional tubular reactor model with advection and possibly axial diffusion is the classical model of distributed chemical reaction systems. This system is described by partial differential equations that depend on the time t and the spatial coordinate z. In this article, semi-analytical solutions to these partial differential equations are developed regardless of the complexity of their initial and boundary conditions and reaction kinetics. These semi-analytical solutions can be used to analyze the effect on the concentrations at the current coordinates z and t of (i) the initial and boundary conditions, and (ii) the reactions that took place at an earlier time. A case study illustrates the application of these results to tubular reactors for the two cases, without and with diffusion.

  • 23.
    Sadegh-Vaziri, Ramiar
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Bäbler, Matthaus U.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Numerical investigation of the outward growth of ZnS in the removal of H2S in a packed bed of ZnO2017In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 158, p. 328-339Article in journal (Refereed)
    Abstract [en]

    Sulfidation of zinc oxide is a viable option for the removal of hydrogen sulfide from raw syngas and biogas. Recent experiments showed that sulfidation of nanoscopic zinc oxide particles leads to an outward growth and the formation of voids inside the particles. In this work, we derive a micro-scale model to describe this phenomenon. The model accounts for nucleation and growth of voids inside the particles, diffusion of Zn and O through the product layer, and deposition of the solid product at the particle surface as a result of the reaction between ZnO and H2S. The model is thus opposite to the well known shrinking core model where an inward growth of the product layer is assumed. To explore the effect of the outward growth on the dynamics of a packed bed adsorber the micro-scale model is combined with a macro-scale model that accounts for intra-pellet diffusion and convection along the packed bed. In the limit of fast nucleation and growth of voids inside the zinc oxide particles, the micro-scale model shows a qualitatively similar conversion profile to the shrinking core model, while when nucleation controls an inflection point in conversion profile is found. On the macro-scale, the outward growth can cause the clogging of pores inside the pellets which prevents the pellets from reaching full conversion. This leads to shorter breakthrough times of the packed bed due to the sealing of unreacted zinc oxide. Our results thus provide a possible explanation of the incomplete conversion of zinc oxide in packed beds.

  • 24. Salazar-Alvarez, G.
    et al.
    Muhammed, Mamoun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zagorodni, A. A.
    Novel flow injection synthesis of iron oxide nanoparticles with narrow size distribution2006In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 61, no 14, p. 4625-4633Article in journal (Refereed)
    Abstract [en]

    A novel synthesis method based on a flow injection technique was developed and the synthesis of magnetite nanoparticles was performed to demonstrate the concept. The technique consisted of continuous or segmented mixing of reagents under laminar flow regime in a capillary reactor. Different schemes of the flow injection synthesis were evaluated and the continuous mode was found to be more advantageous for the synthesis of the iron oxide particles. The material was characterised by X-ray diffraction, thermal analysis, electron microscopy, and magnetic susceptometry. The obtained magnetite nanoparticles had a narrow size distribution in the range 2-7 nm. The influence of chemical parameters and conditions on properties of the material was investigated.

  • 25.
    Ståhl, Marie
    et al.
    KTH, School of Chemical Science and Engineering (CHE).
    Rasmuson, Åke C.
    KTH, School of Chemical Science and Engineering (CHE).
    Towards predictive simulation of single feed semibatch reaction crystallizationSimulation of single feed semibatch reaction crystallization processes2009In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 64, no 7, p. 1559-1576Article in journal (Refereed)
    Abstract [en]

    A population balance model is developed over single-feed semi-batch reaction crystallization of benzoic acid. The model is evaluated by comparison with experimental data, and simulations are carried out to advance the understanding of the process. The model accounts for chemical reaction micro and me, somixing, primary nucleation, crystal growth and growth rate dispersion (GRD). Two mechanistic mixing models are evaluated: the segregated feed model and the engulfment model (E-model) with mesomixing. When the mixing is described by the E-model (engulfment model) and GRD is accounted for, the model quite well captures the influence of reactant concentrations, agitation rate, feed point location, feed pipe diameter, total feeding time and crystallizer volume, on the product weight mean size. When using the SF-model (segregated feed model) the results are less satisfactory. The kinetics of nucleation and crystal growth have a great impact on the results of the simulations, influencing the product weight mean size as well as the response to changes in the processing conditions. A new set of kinetic data for benzoic acid derived from semi-batch experimental results are presented

  • 26. Torbacke, M.
    et al.
    Rasmuson, Åke C.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Influence of different scales of mixing in reaction crystallization2001In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 56, no 7, p. 2459-2473Article in journal (Refereed)
    Abstract [en]

    Experiments on semibatch reaction crystallization of benzoic acid are reported. The conditions in an agitated tank are simulated by a loop reactor by which feed point mixing conditions can be controlled separately from the macroscale circulation rate. Hydrochloric acid is fed into a circulating solution of sodium benzoate and the influence of macromixing, mesomixing and micromixing on the product crystal mean size is evaluated. The product mean size increases with increasing circulation rate in the loop, with increasing feed point mixing intensity, with decreasing feed rate and with decreasing feed pipe diameter. Increased mixing intensity on any level leads to larger product crystals, but especially the rate of mesomixing is of importance. The influence of the feed pipe diameter is opposite to predictions by available theories and cannot be explained by backmixing into the feeding pipe. All results can be correlated quite well against a dimensionless mixing efficiency defined as the ratio of the reactant feeding time to the mixing time. The mixing time is the sum of the time constants for mesomixing and micromixing. A new mesomixing time constant is defined as being proportional to the ratio of the feed pipe diameter and the velocity of the bulk flow passing the feed pipe.

  • 27. Torbacke, Marika
    et al.
    Rasmuson, Åke Christoffer
    KTH, School of Chemical Science and Engineering (CHE).
    Influence of different scales of mixing in reaction crystallization2001In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 56, no 7, p. 2459-2473Article in journal (Refereed)
    Abstract [en]

    Experiments on semibatch reaction crystallization of benzoic acid are reported. The conditions in an agitated tank are simulated by a loop reactor by which feed point mixing conditions can be controlled separately from the macroscale circulation rate. Hydrochloric acid is fed into a circulating solution of sodiumbenzoate and the in#uence of macromixing, mesomixing and micromixing on the product crystal mean size is evaluated. The product mean size increases with increasing circulation rate in the loop, with increasing feed point mixing intensity, with decreasing feed rate and with decreasing feed pipe diameter. Increased mixing intensity on any level leads to larger product crystals, but especially the rate of mesomixing is of importance. The in#uence of the feed pipe diameter is opposite to predictions by available theories and cannot be explained by backmixing into the feeding pipe. All results can be correlated quite well against a dimensionless mixing e$ciency de"ned as the ratio of the reactant feeding time to the mixing time. The mixing time is the sum of the time constants for mesomixing and micromixing. A new mesomixing time constant is de"ned as being proportional to the ratio of the feed pipe diameter and the velocity of the bulk #ow passing the feed pipe.

  • 28. Wang, K.
    et al.
    Bai, B.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    A model for droplet entrainment in churn flow2013In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 104, p. 1045-1055Article in journal (Refereed)
    Abstract [en]

    Understanding the mechanism of droplet entrainment is of great importance for the churn flow. So far, the droplet entrainment mechanism has been experimentally studied; however, no detailed model is available for this particular flow pattern. To address this, the author established an analytical model to better understand the drop entrainment in churn flow. In this model, only the entrainment mechanism named shear-off in equilibrium state is considered and detailed analysis performed for the interface stability based on the Kelvin-Helmholtz instability and force balance acting on the wave crest. The model has been verified using experimental data and different parameters (e.g., pipe diameter, gas and liquid flowrate and pressure) influencing the entrainment is presented. The author proposed a more accurate and reasonable formula for the entrained rate in churn flow based on the existing formula for annular flow. The model developed in this paper predicts the entrainment mechanism under churn flow condition to an accuracy of 30% which is essential for the development of mechanistic models to predict the dryout condition in the future.

  • 29. Wang, K.
    et al.
    Bai, B.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Huge wave and drop entrainment mechanism in gas-liquid churn flow2013In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 104, p. 638-646Article in journal (Refereed)
    Abstract [en]

    A profound knowledge of huge wave and droplet entrainment mechanism is crucial for the thorough study on the gas-liquid churn flow. Although studies have shown that the entrained fraction is high in churn flow and reaches the minimum around the churn-annular transition, the underlying mechanism of the drop entrainment in churn flow is still not well explored. To address this, we investigated the properties of the huge waves and the droplet entrainment in two vertical pipes with the inner diameter of 19. mm and 34. mm under churn flow conditions. We found that the flooding of the film was a characteristic of the churn flow throughout the regime. In addition, increasing the gas or liquid flow rate could lead to the transition from churn flow to annular flow or reverse to slug flow, providing the insight into the differences among slug, churn and annular flow. We also discussed the film instability under different flow conditions and tried to reveal the physical mechanism based on the instability analysis. In our study, the bag breakup and the ligament breakup were observed to coexist. The analysis of the liquid distribution in the cross-section of the pipes not only revealed the variations of the entrained fraction of churn flow from that of annular flow, but also indirectly illustrated the differences between their breakup mechanisms. Moreover, the wave properties (amplitude and frequency) were also analyzed in detail.

  • 30. Wang, Ke
    et al.
    Bai, Bofeng
    Cui, Jiahuan
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    A physical model for huge wave movement in gas-liquid churn flow2012In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 79, p. 19-28Article, review/survey (Refereed)
    Abstract [en]

    A complete knowledge of the huge wave in churn flow is of great importance for the characterization of its entrainment. Huge wave in churn flow is experimentally identified as a highly disturbed wave; however, no specific model is available for this particular wave. Based on the force balance over the wave, we established an analytical model to study its growth and levitation and analyzed the effects of the parameters (including gravity, pressure force of gas and liquid, wall shear stress and interfacial shear stress) on the wave and the gas and liquid flow field. We proposed that the boundary layer in liquid film is more likely to be turbulent rather than laminar and the gas pressure force is the most influential factor. The proposed model was verified qualitatively and quantitatively. We hence theoretically concluded that the churn flow is characterized by the flooding of the film, the flow reversal is attributed to the transition to the annular flow and the pressure gradient decreases with the increase of the gas flow rate. These findings provided insight into the distinction between the churn flow and the annular flow. The wave properties (amplitude and velocity) were analyzed in detail and the churn/annular transition occurred at U* = 1.12. The model helps understand the droplet entrainment in churn flow which is essential for the development of mechanistic models to predict the dryout condition.

  • 31.
    Wetterling, John
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Chalmers University of Technology, Sweden.
    Mattsson, Tuve
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Chalmers University of Technology, Sweden.
    Theliander, Hans
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Chalmers University of Technology, Sweden.
    Modelling filtration processes from local filtration properties: The effect of surface properties on microcrystalline cellulose2017In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 165, p. 14-24Article in journal (Refereed)
    Abstract [en]

    The influence of structure and charge of particles surfaces on the cake filtration behaviour of microcrystalline cellulose was investigated. The local filtration properties were evaluated experimentally and used to model the overall filtration behaviour. At suspension conditions where the microcrystalline cellulose particles are charged, a large pressure drop was observed close to the filter medium, thereby indicating that a rate-limiting skin layer was formed. Measurements of the local solidosity of the filter cake indicated that a secondary filter cake, with a negligible filtration resistance, formed above the rate-limiting skin layer. This behaviour was not observed when the surface roughness of the particles was increased or when the surface charge of the particles was neutralised by making a change to the pH of the suspension. The filtration behaviour of particles with these surface properties was instead dominated by the formation of a compressible filter cake. Local filtration properties of compressible filter cakes determined experimentally were used to successfully model the overall filtration behaviour. The filtration model used an empirical relationship to describe the pressure dependence of the local solidosity of the filter cake along with a cell model to describe the relationship between the solidosity and the permeability of the filter cake.

  • 32.
    Zhan, Caijuan
    et al.
    KTH, School of Engineering Sciences (SCI).
    Hagrot, Erika
    KTH, School of Engineering Sciences (SCI).
    Brandt, L.
    Chotteau, Véronique
    KTH, School of Engineering Sciences (SCI).
    Study of hydrodynamics in wave bioreactors by computational fluid dynamics reveals a resonance phenomenon2019In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 193, p. 53-65Article in journal (Refereed)
    Abstract [en]

    Culture of mammalian or human cells in Wave bioreactor is widely used for cell expansion or for biologics manufacturing. Wave bioreactor cultivation of sensitive cells such as stem cells, immune cells or anchorage-dependent cells, is recognized as an attractive option for culture in suspension or adherently on microcarriers. A systematic optimization of the mixing, oxygen transfer rate and shear stress, most favorable for the cells requires a deep understanding of the hydrodynamics inside the Wave bioreactor bag, i.e. cellbag. Numerical simulation by Computation Fluid Dynamics (CFD), is considered as an inexpensive and efficient tool for predicting the fluid behavior in many fields. In the present study, we perform numerical simulations by Ansys-FLUENT to characterize the flow conditions in a 10 L cellbag. The numerical simulations are carried out to investigate the fluid structures for nine different operating conditions of rocking speed and angle. The influence of these operating parameters on the mixing and the shear stress induced by the liquid motion are studied. We find that the mixing and shear stress increase with the cellbag angle from 4° to 7° but that increasing rocking speeds are not systematically associated with increasing mixing and shear stress. It is concluded that a resonance phenomenon is responsible for the fact that the lowest studied rocking speed, 15 rpm, generates the highest fluid velocity, mixing and shear stress compared to the higher speeds of 22 and 30 rpm.

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