bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of aeration capacity of fermenters
Authors: Linek Václav , Beneš P. , Vacek Václav
Published: August 2005

Important aspects of K1a measurement in agitated aerated vessels are briefly characterized from the standpoint of reliability of the measured data. An analysis of the shortcomings of dynamic methods for measuring the K1a is given. A new modification of the dynamic method is proposed, which excludes these inadequacies through a special experimental arrangement. This was verified by comparing the data with those obtained by an independent steady‐state method. The new method can serve as a standard of reference, suitable for testing newly developed methods for K1a measurement. The initial response method was tested in this way in non‐coalescent liquids, and shown to lead to errors of the order of hundreds of percent. K1a values obtained with the initial response method were found to depend strongly on the probe's location in the vessel.
Porosity and permeametry at sub‐atmospheric pressures
Authors: Igwe Godwin J. I.
Published: August 2005

The Carman‐Kozeny equation is applicable in the viscous flow regime but, as the powder becomes finer, this equation fails. The controlling factor is the ratio of the hydraulic diameter to the mean free path of gas molecules (rH/λ) and, as this approaches unity, “slip flow” occurs. This effect increases with (a) increasing fineness, i.e. rH reduced, (b) decreasing porosity, i.e. rH reduced, and (c) decreasing pressure, i.e. λ increased. In order to account for the enhanced flow arising as a result of this failure, a second term is introduced into the equation and this includes an unknown “constant” (δK0/K), the coefficient of slip. It was considered probable that this so‐called constant was a function of (rH/λ), and an attempt was made to investigate this relationship.
Heat transfer enhancement in fin‐plate heat exchangers by wing type vortex generators
Authors: Brockmeier Udo , Fiebig Martin , Güntermann Thomas , Mitra Nimai K.
Published: August 2005

Heat transfer and fluid mechanical data were computed for laminar channel flows containing strong longitudinal vortex pairs. The strong vortices are generated by thin delta wings and delta winglet pairs of low aspect ratios and large angles of attack. These wings are attached to the channel walls. The data show that longitudinal vortices cause high local peaks in heat transfer and marked increases in the overall channel heat transfer. These increases occur over a wide region of channel wall, compared to the vortex generating wing area. The results are of special interest for compact heat exchangers. The heat transfer enhancement allows a considerable reduction in the heat transfer area which, in turn, reduces the manufacturing and operating costs.
Leakage rates of refrigerants through cracks
Authors: Friedel Lutz , Westphal Frank
Published: August 2005

An independent preliminary mechanistic prediction method for leakage rates through small slit‐shaped through‐wall cracks, based on coupled pressure drop and (critical) mass flux calculation is presented. The predictions are verified against initially subcooled liquid refrigerants and water data collected during experiments in real and model cracks in a wide range of parameters. The achieved accuracy of prediction is already comparable to that of the experimental results. Further model modifications are put forward.
Incorporation of gradient into random search optimization
Authors: Luus Rein , Brenek Paul
Published: August 2005

To improve the rate of convergence of random search optimization procedures, the incorporation of a gradient‐oriented one‐dimensional search is investigated. With this modification to the random search procedure based on uniform sampling and region contraction [1], convergence to within 0.01% of the global optimum was obtained substantially faster for typical chemical engineering problems. It was also found that the reliability of obtaining the global optimum was improved.
Generalization of AIChE and colburn models for tray efficiency
Authors: Koziol Antoni
Published: August 2005

The most important investigations on liquid weeping and entrainment in plate columns with downcomers are reveiwed. The formulae for calculating column plate efficiency under conditions of liquid weeping and entrainment have been derived on the basis of mass balance equations. The presented model is a generalization of the models of AIChE and Colburn. Sample results are shown graphically. The effect of liquid entrainment on tray efficiency predicted by the model is in agreement with experimental data of FRI.
Continuous crystallization of potassium carbonate
Authors: Škrtić Drago , Sangl Reinhard , Kind Matthias , Mersmann Alfons
Published: August 2005

Continuous crystallization of potassium carbonate was investigated in a mixed suspension mixed product removal (MSMPR) crystallizer with 7.0 1 working volume. Highly polydispersed product was obtained, with x50 varying between 320 and 670 μm. Crystal growth rates can be described by the model of Abegg, Stevens and Larson (ASL) (size dependent crystal growth rate). Values of G0 = 8.6 × 10−9 to 3.6 × 10−8 m/s and B0/φ = 2.7 × 108 to 4.2 × 109 1/m3s were obtained for mT = 45 to 92 kg/m3 and ε = 0.45 ± 0.05 W/kg. Nucleation kinetics at 27 °C can be described by the equation: B0/φ = kBφsε0.73G02.5. Since G0 ∝ σ, convection and/or diffusion rather than surface integration are the crystal growth controlling mechanisms.
Studies in liquid‐liquid direct‐contact heat transfer
Authors: Hutchins Joseph F. , Marschall Ekkehard
Published: August 2005

Liquid‐liquid direct‐contact heat transfer in a spray column was studied numerically for a low hold‐up. The solutions of the conservation equations of mass, momentum and energy for both phases agree well with earlier experimental results, if one assumes a rigid liquid‐liquid interface. Heat transfer inside is dominated by transient conduction and natural convection. It was found that the Nusselt number for free convection depends essentially only on the Rayleigh number.
Effect of transfer on droplet size in liquid‐liquid dispersions
Authors: Kleczek Fryderyk , Cauwenberg Veerle , Van Rompay Paul
Published: August 2005

Mean droplet diameter of the dispersed phase in pulsed plate extraction columns was measured for binary and ternary systems. A change in the droplet size in the presence of solute, dependent on such factors as the direction of mass transfer, droplet size in the binary system, radio of diffusion coefficients, viscosity of the continuous phase, interfacial tension and driving force for extraction was observed. Two new empirical correlations of mean droplet sizes in mass transfer conditions are proposed. These correlations have been successfully applied to other extraction columns.
Parameters influencing the mean particle size of a crystalline product
Authors: Mersmann Alfons B. , Kind Matthias
Published: August 2005

Crystallizer design has to take into account the physical and chemical properties of the solution and solids as well as the geometry, type and operating conditions of the crystallizer. The most important property of a crystallizing system is its solubility. High solubility leads to low relative supersaturation and large mean crystal size, and vice versa. High solubility systems can be sensitive to abrasion and attrition. For low solubility systems, mixing is crucial.
The importance of dynamic performance and testing of industrial thermometers in process control
Authors: Chohan R. K.
Published: August 2005

This paper considers the dynamic performance of instruments in control systems. Errors connected with transient measurements are discussed. It is shown that it is not always proper to assign common statistical properties to these dynamic errors. Emphasis is placed on temperature sensors. Common industrial thermometers are described and factors affecting their response discussed. An a‐priori dynamic performance prediction procedure is presented. This permits preinstallation estimation of response characteristics of sensors used in industrial processes. Sensors in service also require performance assessment since they can deteriorate with use. In‐situ testing is useful for this purpose and a recently develolped procedure is described.
Modelling and simulation of monopropellant hydrazine thrusters for spacecraft position control
Authors: Schulz‐Ekloff Günter , Deppner Heinz‐Günter
Published: August 2005

Modelling of the kinetics of a 20‐N hydrazine thruster is carried out by considering two different heterogeneous reaction channels for hydrazine decomposition to the intermediate ammonia. The parameters of the reactor model are estimated by making use of temperature profiles at the wall of the decomposition chamber. Simulated ageing of the catalyst revealed an increase of the rate of deactivation with increasing total firing time.
Modelling of a fluidized bed bioreactor for immobilized enzymes (Part 1)
Authors: Kiesser Torsten , Oertzen Gustav A. , Bauer Werner
Published: August 2005

In the first part of this paper, a mathematical model is presented for a liquid fluidized bed bioreactor using immobilized enzymes with reversible Michaelis‐Menten kinetics. The model is based on the axial dispersion model for the bulk liquid phase. Inter‐ and intraparticle mass transfer as well as enzyme catalyzed reaction inside the porous beads are considered. The overall efficiency of the biocatalysts is calculated by a numerical routine. For the calculation of the concentration profile inside the reactor, a semi‐analytical solution is derived which takes into account the height dependence of the effectiveness factor.
Foam breaking by high speed rotors
Authors: Furchner Bodo , Mersmann Alfons
Published: August 2005

The first part of this paper presents a relationship for the minimum velocity of rotating installations for foam breaking. The derivation is based on equilibrium of inertia and surface forces. Inertia forces occur during the acceleration of foam bubbles and act mainly at the plateau borders. High and definite acceleration can be obtained with a deformer composed of a rotor and a stator. The surface force is due to the dynamic surface tension because surface‐active solutions react to a rapid change in surface area by altering their surface tension. The theoretical relationship is compared with experimental results of minimum velocities needed to break foams produced from aqueous solutions of detergents. The equation presented here explains why measured minimum velocities often range between 10 and 20 m/s. The second part of the paper deals with condensation of continuously generated foam in a closed system. In the process of condensation, foam is not completely separated into liquid and gas phase but turns into foam with small bubbles and high density. The collapse of this condensed foam must be considered for the control of persistent foams in a closed system. The collapse of foams made of aqueous solutions of different surface‐active agents has been investigated. Different highly surface‐active agents show small variations in times of coalescence. A relationship for the lifetime is given, which is based on laminar flow along plateau borders. Recommendations are made with respect to the geometry of the foam breaker, scale‐up and operating variables such as rotational speed of the foam breaker and gas flow rate.
Influence of geometric and thermophysical properties of reaction layer on sulphur dioxide oxidation in transient conditions
Authors: Sapundzhiev Christo , Grozev Georgi , Elenkov Dimiter
Published: August 2005

The sulphur dioxide to sulphur trioxide oxidation process in a fixed bed catalytic reactor is simulated in the case of cyclic change in the direction of the reaction mixture feed. It is shown that, for transient condition, the amount of catalyst in the reactor may be substantially reduced by its partial substitution with inert material of suitable form, dimensions and thermophysical properties, at the end of the layer. This makes the direct regenerative heat transfer process in these zones controllable, producing the same conversion and overall height of the layer. The results are significant for sulphuric acid production from gases poor in sulphur dioxide.
Sodium compounds as catalysts for methanol dehydrogenation to water‐free formaldehyde
Authors: Meyer Andreas , Renken Albert
Published: August 2005

Formaldehyde is produced industrially from methanol by partial oxidation of oxidative dehydrogenation. In these processes, water is formed as a by‐product. Anhydrous formaldehyde is required for many syntheses and, therefore, its production is of potential interest. In the present study, catalysts based on alkali compounds were found to be active in the dehydrogenation of methanol if absence of oxygen. Sodium carbonate doped with indium shows a selective of up to 75% for methanol conversion not exceeding 60%.
Characterization of Cu and K containing Fe/Mn oxide catalysts for fischer‐tropsch synthesis
Authors: Grzybek Teresa , Klinik Jerzy , Papp Helmut , Baerns Manfred
Published: August 2005

Copper and potassium containing Fe/Mn oxide catalysts for Fischer‐Tropsch synthesis were investigated by X‐ray microprobe technique, scanning electron microscopy, low‐temperature argon sorption and carbon monoxide and carbon dioxide chemisorption at −80°C. The specific surface areas of the catalysts depend on the preparation method, e.g. addition of K or Cu by coprecipitation leads to an increase while impregnation results in a decrease in surface area. The resulting samples are inhomogeneous, as shown by all method. Mn and especially K accumulated on the surface of the catalysts. Addition of Cu and K considerably altered the selectivity and activity of the Fe/Mn oxide catalyst. High potassium contents produced high olefin to paraffin ratios but these catalysts became rapidly deactivated. Copper and a very small addition of potassium led to a very low olefin to paraffin ratio but showed a high and constant activity.
Motionless mixers for the design of multitubular polymerization reactors
Authors: Tien Nguyen Khac , Streiff Felix , Flaschel Erwin , Renken Albert
Published: August 2005

Experimental investigations of thermal bulk polymerization of styrene in pilot plants of different sizes have been performed. Each pilot plant is composed of a tubular recycle reactor, connected in series with a tubular reactor, both completely filled with Sulzer motionless mixers. Kinetic, reactor and viscosity models have been verified in a wide range of styrene conversions (up to 96%) temperatures (up to 210 °C) and polystyrene molar masses (up to 360 000). Scale‐up studies were carried out which confirmed that multitubular reactors of special design can be applied for industrial polymerization process.
Transport effects in catalytic fluidized‐bed reactors
Authors: Shaikh Abdulla A. , Carberry James J.
Published: August 2005

The majority of the fluidized‐bed reactor models are models are rooted in the tacit assumption that transport between the bubble, cloud, and emulsion phases occurs in series with chemical reaction. A more realistic model that anticipates simultaneous transport and reaction is presented in terms of a fluid‐bed effectiveness factor which embraces the limits between chemical and mass transport control. Analysis of the predictive capacity of this model vis‐a‐vis the Kunii‐Levenspiel model reveals signal differences in chemical conversion.
A fluid‐dynamically based model of bubble column reactors
Authors: Gasche Hans‐Erich , Edinger Christine , Kömpel Harald , Hofmann Hanns
Published: August 2005

A heterogeneous fluid dynamic model has been developed to describe the complex flow structure of two‐phase in bubble columns. The equation of continuity and momentum balances form the basis of the model. Coupling of the two phases occurs via an interaction force, deduced by a force balance around a single rising bubble. Multiphase flow mixing processes are taken into consideration by introducing turbulent viscosities of the two phases involved. The Simulation program was extended to reactive system, taking into account the mass balances of a second order gas‐liquid chemical reaction as well as the different absorption/reaction regimes. The gas phase concentration profiles show pronounced axial and radial dependences, while the liquid phase can be regarded as a CSTR with respect to the liquid component. With reference to the gaseous component, which is being absorbed in the liquid phase, the degree of back mixing does not show CSTR behaviour as the influence of different absorption conditions in different axial and radial reactor positions is superposed on that of turbulent motion of the liquid carrier of the dissolved gaseous component.
A reaction model for the electrochemical synthesis of adipontrile
Authors: Scott Keith , Hayati B. , Haines Alistair N. , McConvey Ion F.
Published: August 2005

A theoretical and experimental study of the electrohydrodimerization process to produce adiponitrile is used to determine an appropriate reaction model. From numerical simulations of five proposed reaction schemes and subsequent comparison with experimental data, the most favoured route is via an anion, intermediate of acrylonitrile. This route, a five step reaction involving electrochemical and chemical reaction in a diffusion/reaction layer, gives good predictions of product distributions over a wide range of current densities and acrylonitrile concentrations of product distributions over a wide range of current densities and acrylonitrile concentrations.
Search for optimal geometry of a conical turbine agitator for heat transfer in stirred vessels
Authors: Strek Frederyk , Karcz Joanna , Bujalski Waldemar
Published: August 2005

Simultaneous measurements of power consumption P and heat transfer coefficient α for a jacketed, baffled, agitated vessel of diameter D = 0.45 m, equipped with a conical turbine, were carried out. The following geometric parameters of the agitator were tested: diameter d, blade width b and number Z, and distance from the bottom of the vessel to the lower edge of the blade h. The results of these investigations were generalized mathematically. On the basis of optimization, the best geometric parameters with respect to heat transfer are proposed for the conical turbine agitator.
Monte carlo simulation of transient CSD in a continuous crystallizer
Authors: Gupta Bhaskar Sen , Dutta Tapas Kumar
Published: August 2005

A Monte Carlo simulation scheme is proposed for transient crystal size distribution in a continuous crystallizer. The suggested scheme can taken into account dispersion effects of growth rate, shape factor and birth size on crystal size distribution. This method is simple and more versatile than solution of the number balance equation or the finite‐state Markov chain model. The proposed algorithm of the process has a very simple structure and can be easily implemented on a personal computer. The present contribution is extension of an earlier work of Sen Gupta and Dutta.
Cooling of arc furnace electrodes with heat pipes
Authors: Bullerschen Klaus‐Gerd , Wilhelmi Herbert
Published: August 2005

Combination electrodes with water cooling shanks, which have been introduced to reduce graphite consumption in UHP furnaces, cause the danger of vapour explosions in case of breakIng. Heat pipes are highly efficient two phase heat conductors which could provide a safer alternative to water cooling shanks, since they contain only a small amount of liquid. The transport of energy results from evaporation of the working fluid in the heated section, convection of the vapour to the cooled section and reflux of the condensed fluid to the heated end. Large heat quantities can be transferred under nearly isothermal conditions within the tube, as long as certain limits are not exceeded. The operating temperature can be controlled by design parameters such as the thermal resistance of the cooling zone. The proper function of heat pipes for cooling arc furnace electrodes is investigated by comparing the calculated heat load with temperature dependent limits to heat transport. It is shown that copper tubes with water as the working fluid combine efficient cooling and safe performance in the low temperature range, while the cheaper steel tubes with sodium filling are suitable for high temperature operation.
Adsorption and desorption of halogenated hydrocarbons using activated carbon
Authors: Schäfer Manfred , Schröter Hans‐Jürgen , Peschel Gerhard
Published: August 2005

Environmental hazards caused by halogenated hydrocarbons and increasingly stringent regulations for limiting their emission require comprehensive investigations of these substances. The present work deals with the adsorption and desorption of halogenated hydrocarbons on activated carbon. The results could be useful in the utilization of landfill gases because halogenated hydrocarbons must be removed in order to avoid pollution and the loaded activated carbons have to be regenerated. Activated carbons are well suited to removal and recovery of halogenated hydrocarbons from gas flows.
Coke removal from a zeolite catalyst by supercritical fluids
Authors: Manos Georgios , Hofmann Hanns
Published: August 2005

In the study of the possible coke removal from zeolite catalysts, the solubility of polyaromates in supercritical fluids (SCF) was determined, showing that it becomes drastically reduced with increasing molar mass. Experiments with supercritical ethyl benzene and benzene showed that only coke precursors can be dissolved and, therefore, complete coke removal by SCF is impossible but it has been confirmed that, under supercritical conditions, deactivation of the catalyst could be slowed down.
On the falling‐rate period
Authors: Schultz Peter
Published: August 2005

A fixed bed of glass particles, wetted with water, was dried from above. The measured moisture profiles within the sample show that its surface is not completely dry during the falling‐rate period. Hence, the current view, according to which the moisture front retreats into the sample directly after reaching the critical moisture content, has to be revised. Assuming that parallel dry and wet channels form within the sample during the constant‐rate period, the onset of the falling‐rate period depends only on the diameter of these channels. If the moisture is distributed very finely, a large number of channels with a small diameter have to be considered. The falling‐rate period for this system occurs at low moisture contents. For a coarse distribution of moisture, fewer channels with a large diameter should be assumed. Their drying rates show the beginning of the falling‐rate period already at high moisture contents. A good agreement between measured and calculated drying rates could be achieved by fitting the channel diameter. Only for very low moisture contents, is the agreement poor. This is to be expected, because the measured moisture profiles show a completely dry sample surface for these moisture contents, indicating that the moisture front has already retreated into the sample.
Mass transfer to regular packings in single phase
Authors: Colazo Jorge A. , Nieva Isabel A. , Böhm Ursula
Published: August 2005

A study of mass transfer to regular packings by the electrochemical technique is presented in this paper. The excellent properties of radial mixing were verified and the correlation for mass transfer rate was also obtained. It was found that the energy efficiency, which is represented by the LeGoff number, is higher than that of other packings due to the low pressure drop shown by these arrangements.
Theoretical analysis of gas stripping performance of spray towers
Authors: Beg Shafkat A. , Rehman Syed Obaidur , Hassan Mirza M.
Published: August 2005

A simplified model has been developed to describe ammonia stripping process in spray towers. The effect of various operating parameters including air flow rate, contact time, droplet size, liquid to gas ratios and tower height on the performance of such systems has been studied in detail. The results obtained for ammonia stripping have been compared with the limited experimental data available in literature. The predicted results agree reasonably well with the reported experimental data.
Sensitivity analysis in static optimization of fermentation plants
Authors: Posten Clemens
Published: August 2005

Biotechnological processes are often characterized by uncertain model parameters, input variables which are difficult to handle and ill defined cost functions. Nevertheless, it is desirable to define optimal operating points. Starting with a robust approach for numerical optimization, the paper presents three different methods for evaluating the sensitivity of an optimal operating point to uncertain parameters or disturbances of the input variables. It is shown that sensitivity analysis can provide useful guidelines for designing biotechnical plants with invariant optimum operation in the presence of changing inputs or parameters.
Particle structure change of CaO during high temperature sulphatization
Authors: Bjerle Ingemar , Ye Zhicheng
Published: August 2005

The effects of particle size (layer thickness), BET surface area and pore size distribution on the reactivity of CaO derived from limestone were studied by using a pH‐stat and the BET method. Visual analysis was obtained with SEM, and X‐ray diffraction was used to determine the crystalline components present. It was found that the pore size distribution, including pore volume and pore surface distribution, affected the sulphatization behaviour. The larger pores (D > 50 Å) with their pore volume and pore surface were to some extent responsible for both initial reactivity and ultimate capacity of CaO.
Method of multiobjective optimization for imprecise objectives
Authors: Kraslawski Andrzej , Rzyski Edward , Stelmach Jacek
Published: August 2005

A method of multiobjective optimization for imprecise objectives is presented. The problem consisted in a minimization of the distance between the set of admissible solutions and an ideal point. Applicability of the method is illustrated by the choice of best impeller from a group of seven different types tested. The optimum process conditions were selected, taking as optimization objective the maximization of kLa and minimization of PG.
Performance of construction materials in multiphase liquid/solid flows
Authors: Ehmann Ingo , Heitz Ewald
Published: August 2005

The transport of corrosive liquids containing solids, in conventional energy and process technology as, for example, in oil and gas production, places high demands on the selection of materials for plant construction. A discussion on the chemo‐mechanical load demonstrates the significance of hydrodynamics in selecting the test method. Choosing a pipe with an abrupt expansion of cross‐section as a flow model yields a new method of simulating operation conditions. By subjecting ferrous materials used for hydraulic machinery to representative media from three important industries, a broad spectrum of results can be obtained. Classification of the results leads to four basic types of mass loss behaviour in materials as functions of flow rate. These findings yield guidelines for the selection of materials and the dimensioning of flow equipment.
Water determination in pyrolysis gases using calcium carbide
Authors: Lindblom Mats , Andersson Lars A. , Bjerle Ingemar
Published: August 2005

A method for the measurement of water content in a flowing gas has been developed. It consists in passing warm moist gas through a bed of CaC2 where the water vapour is adsorbed and reacts directly with the carbide to form C2H2, which is then analyzed in a gas chromatograph. In this work, water vapour concentrations ranged from 1000 to 13000 ppm at a minimum pressure of 10 bar. The method has also been applied in a number of pyrolysis experiments.
Kinetics of carbon dioxide absorption in aqueous solutions of diisopropanolamine
Authors: Sotelo Jose L. , Benitez F. Javier , Beltran‐Heredia Jesus , Rodriguez Concepcion
Published: August 2005

A bubble column absorber was used to investigate kinetics of the reaction between carbon dioxide and aqueous solutions of diisopropanolamine (DIPA), by means of gas absorption experiments. These were conducted in the temperature range of 20 to 40°C, with DIPA concentrations from 5 to 500 mol/m3, and CO2 partial pressures between 5 and 101 kPa. A model based on the Danckwerts' surface reneval theory was used to analyze the experimental results and to determine the rate constant. The obtained data support the assumption of a second‐order overall reaction, with the rate constants being well correlated by the Arrhenius equation:
Agitation and effective nucleation in forced circulation magma crystallizers
Authors: Gerigk Markus J. , Offermann Hans
Published: August 2005

A new model is derived to establish the effective nucleation rate in terms of the MSMPR‐theory. The model is based on the concept of two‐step crystal growth, secondary nucleation, nuclei activation and metastable supersaturation. A comparison between model prdictions and experimental data from different crystallizers is presented. This model, which integrates hydrodynamics directly into its theory, proves to be extremely suitable for describing the MSMPR‐crystallization process.
Degradation of lignin with monomethylamine
Authors: Peter Siegfried , Gotz Rolf
Published: August 2005

Wood chips were treated with gaseous mixtures of monomethylamine and water vapour at temperatures between 160 and 120°C and pressurs ranging between 1.5 and 7.0 MPa. The degradation products were subsequently extracted with different solvents at ambient pressure. First, The degradation products of lignin were extracted with highly selective organic solvents such as diethyl ether or 2‐butanone. Then, the remaining decomposition products were extracted with water or an aqueous solution of monomethylamine. The latter extract contains the degradation products of the hemicelluloses in a relatively high concentration. After a three hour digestion, the residue obtained from spruce had a lignin content of 3.1 wt‐% (pine: 3.7 wt‐%; birch 0.3 wt‐%). The total yield of unbleached cellulose was approximately 60 wt‐%.
Liquid circulation in columns due to bubble drift
Authors: Millies Marco , Mewes Dieter
Published: August 2005

The profiles of liquid velocity and gas hold‐up in convection cells of bubble columns were calculated numerically. Development of a circulation cell was calculated from momentum and mass balances. Breakdown of the circulation cell was calculated taking into account the drift motion of bubbles ascending in accordance with the velocity gradient of the liquid. A limit of stability for the development of circulation cells has been obtained.
Characterization of a photochromic triaryl methane dye sulphite for use as a tracer in the visualization of water flows
Authors: Douglas Peter , Enos Richard D.
Published: August 2005

The chemical and photochemical properties of a photochromic water soluble triaryl methane dye sulphite, acid magenta monomethyl magenta sulphite, (AMMM · SO3)4−, have been examined, and the application of this photochromic system to the visualization of water flows is discussed. Addition of sulphite to an aqueous solution of the parent dye acid magenta monomethyl magenta, AMMM2−, (a methylated derivative of acid magenta, C.I. acid violet 19) leads to formation of the colourless sulphite complex, (AMMM · SO3)4−. Pulsed irradiation of a solution of this compound, with light of wavelength shorter than ≈ 340 nm, causes transient production of the parent dye, whose lifetime is influenced by pH, sulphite concentration, temperature and ionic strength. Longest useful lifetimes are of the order of a few seconds and a general equation is presented for the calculation of dye lifetimes for a variety of conditions. The complex formation constant for (AMMM · SO3)4− is 1.8 (± 0.2) × 105 M−1, while that for the weakly photochromic hydroxide (AMMM · OH)3− is 1.3 (± 0.3) × 106 M−1. The quantum yield of dye production at 308 nm is ≈ 0.5 – 1.0, and this is discussed along with the absorption spectra of AMMM2− and (AMMM · SO3)4− with respect to the penetration characteristics of a pulse of 308 nm laser radiation with an energy of a few millijoules. The action spectrum for dye production from (AMMM · SO3)4− suggests that there is a non‐photochromic absorption band at about 350 nm, an assumption which is supported by the failure to detect efficient dye production when using 355 nm excitation from a Nd/YAG laser.
Optimization and adaptive control of a semi‐batch synthesis reactor
Authors: Uhlemann Jens , Cabassud Michel , Le Lann Marie‐Véronique , Borredon Elisabeth , Casamatta Gilbert
Published: August 2005

The optimization of a chemical synthesis aims at an adjustment of the operating conditions, i.e. pH, temperature and initial concentrations, in order to obtain maximum yield, minimum operating costs or similar. The optimization effort may be considerable so that, in many cases, its cost cannot be justified, especially for small volume products. This paper introduces a new strategy, namely to establish the optimum operating conditions with a relatively small effort. The new approach is illustrated by the synthesis of 2‐furyl oxirane. In the first step, a simplified mechanistic process model has to be determined on the basis of easily accessible experimental data. Initial and final concentrations of all reacting components, reaction time and temperature must be known. A two‐step evaluation yields the stoichiometric coefficients of all the occurring reactions as well as the parameters of the Arrhenius model. This so‐called trend model is used in the optimization of the operating conditions. It is not only important to know the optimum operating conditions but also to maintain them as close as possible in practical operation. An adaptive controller is well suited to such an application and its use is discussed.
Kinetics and mechanism of oxidative coupling of methane over sodium‐manganese oxide catalyst
Authors: Golpasha Rahmatolah D. , Karami Davood , Ahmadi Reza , Bagherzadeh Ebrahim
Published: August 2005

The kinetics of methane oxidative coupling (OCM) was studied using 1 g of Na‐Mn2O3 catalyst at 1073 to 1123 K, in an integral flow reactor (I.d. = 10 mm), at atmospheric pressure with methane and oxygen partial pressures of 0.27 and 0.13 bar, respectively, so that the ratio of CH4 to O2 was 2. The flow rate range was 50 to 200 ml/min. the kinetic data were analyzed by the Rideal‐redox type of rate equation assuming the methyl radical and active surface oxygen to be the steady‐state intermediates. Oxidation and reduction rate constants (Kox, Kred) for methane consumption were calculated from experimental catalysis results by computer simulation using the multiple least squares method. The activation energies at rate constants Kox and Kred for this type of catalyst were reported as 43.26 and 62.2 kcal/mol, respectively.
Liquid phase oxidation of α‐pinene initiated by ozone. 1. Conversion of α‐pinene and formation of its hydroperoxide
Authors: Encinar José María , Beltrán Fernando J. , Frades Jesús María
Published: August 2005

The use of ozone as initiating agent in the liquid phase oxidation of α‐pinene has been investigated. The first intermediate product of the reaction is the hydroperoxide of α‐pinene. Both, ozone partial pressure and its initiation time exert an inhibiting effect on the conversion of α‐pinene but yield higher selectivities for the hydroperoxide of α‐pinene compared with those of oxidation without ozone. In all cases, temperature was found to be the most important variable affecting the oxidation rate. From a mechanism of radical reactions, kinetic equations, consistent with the experimental results, corresponding to α‐pinene oxidation rate and net formation rate of its hydroperoxide, were obtained. The rate constants are given as functions of temperature. The results also suggest that a fraction of the hydroperoxy radicals decomposes to yield other products such as verbenol and verbenone, identified in this work, and whose kinetics will be reported in a later paper.
Thermal analysis of solids production processes
Authors: Mersmann Alfons , Franke Jürgen
Published: August 2005

The present work investigates the energy consumption of a solids production process. Such a process consists of three different operation units: crystallization/precipitation, solid‐liquid separation by centrifuges or filters and drying of wet crystals. Each unit is analyzed with the objective of minimizing the energy consumption. Operating conditions, process design and other characteristic parameters (crystal size, porosity and physical proporties) are discussed with the aim to evaluate their influence on the process.
Transient behaviour of an impulsively heated fluid
Authors: Brown Matthew A. , Churchill Stuart W.
Published: August 2005

Approximate as well as reasonably exact numerical solutions of the equation of conservation have previously predicted that sudden heating of a solid surface adjacent to a region of gas will generate a slightly supersonic wave with small positive amplitudes in pressure, temperature and density, and thereby a small mass velocity in the direction of wave propagation. If the gas is confined by a second parallel surface, the wave is predicted to be reflected repeatedly from both surfaces and to decay slowly due to viscous and thermal dispersion. This process, which has been termed thermoacoustic convection, is presumed to result in transient heating of the confined gas and heat transfer through it at rates greatly exceeding that of pure thermal conduction. The current work constitutes the first quantitative experimental confirmation of this behaviour. Numerical solutions obtained for support and guidance of the experimental work define for the first time the conditions required for the generation of a wave of significant strength.
Effect of filling method on the packing distribution of a catalyst bed
Authors: Šmíd Jiří , Van Xuan Pham , Thýn Dr. Jiří
Published: August 2005

The bulk density of a catalyst bed in two‐dimensional reactor model has been measured by a radiogauging method. Three ways of introducing the catalyst were used. Attention was paid to bulk density near the wall and the bottom of the model. A homogeneous distribution of the catalyst was obtained in the case of the “rainy” (uniform) filling method using a grid distributor.
Bed collapse technique for estimating parameters of generalized wake model for a three‐phase fluidized bed
Authors: Jin Yong , Zhang Junping , Yu Zhiqing
Published: August 2005

The hydrodynamic behaviour of a cocurrent gas‐liquid‐solid fluidized bed was studied by using the bed collapse technique. The key parameters, k and x, of the generalized wake model were estimated. Compared with other existing methods for evaluating the parameters k and x, the bed collapse technique shows some distinct advantages. Parameters are derived directly from experiments in a three‐dimensional three‐phase fluidized bed and there is no need to assume that a bubble and its wake form a perfect sphere. Hold‐up data of the three‐phase fluidized bed predicted by the generalized wake model with k and x estimated by the bed collapse technique are in good agreement with those obtained via the traditional pressure‐drop method.
Influence of solids concentration and static mixers on fluid dynamics in three‐phase fluidized bed bioreactors
Authors: Potthoff Matthias , Bohnet Matthias
Published: August 2005

The influence of solids concentration and static mixers on the hydrodynamics of the gas phase was studied for a three‐phase fluidized bed bioreactor (air, nutrient solution, biocatalyst Ca alginate beads). Axial gas hold‐up profiles, radial gas velocity profiles, mean bubble diameter and gas/liquid interfacial area per unit volume were measured in a bubble column (DR = 0.142 m, HR = 1.748 m). The influence of solids concentration on the gas hold‐up is insignificant; static mixers enhance the gas hold‐up in the reactor volume element in which they are installed. Axial gas velocity decreases with increasing solids concentration. At high solids concentrations, static mixers exert little influence on the gas phase but, at low concentrations, they do. A model is suggested to describe the influence of solids concentration (characterized by turbulent viscosity vt) and static mixers (characterized by profile parameter n) on the gas velocity profile.
Interfacial tension in systems with a supercritical component at high pressures
Authors: Hiller Norbert , Schiemann Hartmut , Weidner Eckhard , Peter Siegfried
Published: August 2005

Interfacial tension of the binary systems pelargonic acid/ethane, pelargonic acid/carbon dioxide, linoleic acid/ethane, and linoleic acid/carbon dioxide was measured at 313, 333, and 353 K and pressures ranging up to 250 bar, using the capillary rise and Du Nouy ring methods. Both these methods yield similar values. The surface excess of supercritical components is deduced from the measurement results with the aid of Gibbs adsorption equation. The surface excess concentration increases with increasing gas activity, runs through a pronounced maximum, later decreasing rapidly to very small values. Near the surface excess maximum, a falling film of fatty acids disintegrates into a mist of tiny droplets.
Extraction of zinc by alkyl thiophosphoric acids with emulsion liquid membranes
Authors: Vasconcelos Jorge M. T. , Carvalho Jorge M. R.
Published: August 2005

Treatment of a given multicomponent cationic mixture was studied applying the emulsion liquid membrane (ELM) separation technique for Zn recovery. Experimental apparatus and conditions are described. Comparative studies using two zinc‐selective ion exchangers (thio‐DEHPA and dithio‐DEHPA) were carried out whereby the composition of the liquid membrane and the operating conditions were investigated for both extractants. A useful method of representing the concentrations of the feed and the receiving aqueous phase is proposed, which allows the occurrence of break‐up and/or osmosis to be easily detected.
Pellet heat transfer coefficients in packed beds: Global and local values
Authors: Wijngaarden Ruud J. , Westerterp K. Roel
Published: August 2005

Pellet heat transfer coefficients in a packed bed have been obtained, both for specific individual pellets and for the entire bed. They are referred to as local and global values, respectively. It appears that the local values are scattered around the global value. This is due to the heat transfer coefficient of individual pellets being statistically distributed, as a result of the randomnes of the packing. At low Reynolds numbers, both global and local values fall well below Nu = 2, which is the lower limit for a single sphere in absence of convection. In the literature, this behaviour has been attributed i.a. to axial dispersion and fluid maldistribution. However, these phenomena cannot explain why the same behaviour is observed in slurries. The fact that the local values fall below Nu = 2 would suggest that neither of these explanations is valid for packed beds.
Investigations on hydrodynamics of radial flow moving bed reactors
Authors: Song Xuqi , Wang Zhanwen , Jin Yong , Gong Meishan
Published: August 2005

Distributions of pressure and velocity in the main channels were studied in a radial flow cold model of a moving bed reactor, 500 mm in diameter, in four different gas flow modes, inward Z gas flow, inward Π gas flow, outward Z gas flow, outward Π gas flow. It has been found that, in outward Π gas flow mode, the axial non‐uniformity of the gas is at a minimum. The following correlations are proposed for the momentum recovery factors Ka and Kb:

Ka = 0.684 + 0.0128 (du/dx)/u,

Kb = 1.135 + 0.0158 (du/dx)/u.

Pressure distributions in the main channels can be accurately predicted using Ka and Kb.
Distribution of energy dissipation rate in an agitated gas‐liquid system
Authors: Fořt Ivan , Machoň Václav , Kadlec Petr
Published: August 2005

This contribution presents a theoretical description of the relationship between the rate of energy dissipation per unit volume and the mean kinetic energy of turbulence per unit volume in a mechanically agitated gas‐liquid system. For agitated systems with standard (Rushton) turbine impellers, the effect of the aeration rate on the distribution of the rate of energy dissipation per unit volume in the system was investigated. It follows from the experiments carried out that the gas flow rate significantly affects the rate of energy dissipation per unit volume in the impeller region as well as in the bulk of the agitated batch. In the impeller region, the investigated rate of energy dissipation markedly increases with increasing gas flow rate and, in the remaining part of the agitated batch, it decreases. Moreover, the rate of energy dissipation near the impeller depends strongly on the local gas hold‐up which corresponds to the regime of two‐phase flow behind the impeller blades (i.e. to the occurrence of clinging of ragged cavities).
Correlation and prediction of gas solubility in heavy complex liquids
Authors: Mandagarán Beatriz A. , Campanella Enrique A.
Published: August 2005

A lattice‐gas model is used for calculating the solubilities of light gases in heavy complex hydrocarbons. For waxes, the model gives a good prediction of the solubilities on using the molecular weight of the liquid to describe the solvent. For crude oils and coal‐derived liquids, the prediction is of only modest quality. However, it does improve on using experimental Henry's constants.
Reactive liquid‐liquid test system Zn/Di (2‐ethyl hexyl) phosphoric acid/n‐Dodecane. Equilibrium and kinetics
Authors: Wachter Bruno , Bart Hans‐Jörg , Moosbrugger Thomas , Marr Rolf
Published: August 2005

This contribution reviews the models for equilibrium and kinetics of the system Zn/D2EHPA/n‐dodecane (and other diluents), published during the past decade, as well as values of the appropriate model parameters, i.e. of equilibrium and reaction rate constants. The reviewed kinetic models comprise those for kinetic, diffusional and mixed mass transfer regimes. It is shown that, under certain conditions, the rate equation within the kinetic regime has the same mathematical structure as the equations for the overall mass transfer rate within the diffusional and mixed mass transfer regimes. This means that the same equation interprets experimental data from each of the three regimes. Thus, a fit of experimental data to a model is not sufficient for discriminating between the mass transfer regimes. Results of kinetic experiments, using a stirred mass transfer cell with constant interfacial area, are presented.
Hybrid modelling of yeast production processes – combination of a priori knowledge on different levels of sophistication
Authors: Schubert Jörg , Simutis Rimvydas , Dors Michael , Havlík Ivo , Lübbert Andreas
Published: August 2005

Process models are used to formulate knowledge about process behaviour. They are applied, e.g., to predict the process' future behaviour and for state estimation when reliable on‐line measuring techniques to monitor the key variables of the process are not available. There are different sources of information available for modelling, which provide process knowledge in different representations. Some elements or aspects may be described by physically based mathematical models and others by heuristically obtained rules of thumb, while some information may still be hidden in the process data recorded during previous runs of the process. Heuristic rules are conveniently processed with fuzzy expert systems, while artificial neural networks present themselves as a powerful tool for uncovering the information within the process data without the need to transform the information into one of the other representations. Artificial neural networks and fuzzy technology are increasingly being employed for modelling biotechnological processes, thus extending the traditional way of process modelling by mathematical equations. However, a sufficiently comprehensive combination of all these techniques has not yet been put forward. Here, we present a simple way of combining all the available knowledge relating to a given process. In a case study, we demonstrate the development of a hybrid model for state estimation and prediction on the example of a yeast production process. The model was validated during a cultivation performed in a standard pilot‐scale fermenter.