bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluid mechanics of circulating fluidized beds
Authors: Wirth Karl‐Ernst 
Published: August 2005

AbstractA fluid mechanical model of segregated vertical gas‐solids flow has been developed. Mass and force balances were set up with the aid of this model and, finally, a dimensionless state and pressure drop diagram was calculated. In this diagram, the pressure gradient caused by the solids transport is plotted in dimensionaless form versus the superficial gas velocity in the form of a particle Froude number. Parameter is the ratio of the solids volumetric flow rate at minimum fluidization to the gas volumetric flow rate. The state and pressure drop diagram is valid for a given gas‐solids system, i.e. for a given Archimedes number and given minimum fluidization porosity. The fluid mechanical behaviour of different types of circulating fluidized beds can be explained with the aid of the state and pressure drop diagram for segregated vertical gas‐solids flow. As an example, the operating behaviour of circulating fluidized bed with a syphon in the solids downcomer is discussed. Measurements of the circulating solids mass flow rates are compared with calculation results.
Non‐steady‐state catalytic decontamination of waste gases
Authors: Sapundzhev Christo , Grozev Georgi , Elenkov Dimiter 
Published: August 2005

AbstractThe non‐steady‐state behaviour of a fixed bed reactor controlled by periodical direction reversal of reactant feed, applied in catalytic oxidation of industrial waste gases, containing organic compounds and carbon monoxide, has been investigated. The effects of the type of oxidized compound, its initial feed concentration, linear gas velocity, inerts‐to‐catalyst ratio and inerts thermophysical characteristics on the formation of reactor concentration and temperature fields were elucidated. It was shown that autothermal reactor behaviour is guaranteed by concentrations of the oxidized component which ensure an adiabatic temperature increase in excess of 20 °C. Deviations of either flow rate or initial concentration of the oxidized compound do not disturb the operational stability.
Three‐component mass transfer in liquid‐liquid extraction with the system glycerol‐acetone‐water. Part 2: Calculation and experimental investigation of three‐component mass transfer in a countercurrent extraction column
Authors: Schermuly Wolfgang , Blaß Eckhart 
Published: August 2005

AbstractThis article describes the effects which occur during three‐component mass transfer in liquid‐liquid extraction between saturated and undersaturated phases of the system glycerol‐acetone‐water. The description is based on experiments in a countercurrent spray column. The physical modelling starts with the balance equations of phase flows, taking into account the variation of concentrations and mass flow rates along the column axis as well as backmixing effects. In addition, recent findings on the mechanisms of mass transfer in saturated and undersaturated phasses, deduced from theoretical and experimental results, were used to formulate mass transfer coefficients. These are valid for the region near the interface of drops in a fluid and are inserted into the balance equations. A comparison between experiments and calculations of the observed phenomena is presented.
Fluidized bed dryers: Dynamic modelling and control
Authors: Panda Rames C. , Rao Vadarevu S. Ramachandra 
Published: August 2005

AbstractFluidized bed drying finds important applications in the chemical industry on account of the following advantages: (a) rapid exchange of heat and mass between drying media and particles yields the desired product quality and reduces the overall drying time and (b) easy handling of feed and product. There is much scope for improving the existing modelling techniques as applied to predicting the performance characteristics of the dryers. This should provide a sound basis for the implementation of appropriate control strategies. This report is a review of prevailing modelling, identification techniques and control strategies. Hopefully, the up to date information in this paper will be found useful for research work on fluidized bed dryIng.
Role of sparger design in mechanically agitated gas‐liquid reactors. Part I: Power consumption
Authors: Rewatkar Vilas B. , Joshi Jyeshtharaj B. 
Published: August 2005

AbstractPower consumption (Part I) and liquid phase mixing time (Part II) were measured in 0.57, 1.0 and 1.5 m i.d. vessels. A pitched blade downflow impeller (PTD) was used. Design details of the PTD impeller such as diameter (0.22T to 0.5T), blade width (0.25D to 0.4D) and blade thickness (2.8, 4.3 and 6.4 mm) were studied. The effect of sparger type and geometry on power consumption has been investigated. For this purpose, pipe, ring, conical and concentric ring sparger were employed. Design details of the ring sparger such as ring diameter, number of holes and hole size were also studied in depth. Sparger location with respect to the impeller was found to be the most important parameter and was therefore varied for nearly all the spargers studied. A correlation for the power consumption has been developed.
Impact of particle size dispersity on thermal conductivity of packed beds: Measurement, numerical simulation, prediction
Authors: Tsotsas Evangelos , Schlünder Ernst‐Ulrich 
Published: August 2005

AbstractThe influence of particle size dispersity on thermal conductivity of packed beds without fluid flow is investigated. For this purpose, new experimental data for bi‐ and polydispersed packings are presented and data from the literature reviewed. All data are tabulated. The results of numerical calculations carried out for regular arrangements of spheres are also discussed. The impact of particle size dispersity on thermal conductivity is shown to be primarily due to the change in bed porosity. Thus, prediction can be carried out in the same way as for monodispersed packings if based on the actual bed porosity. A model developed by Schlünder and co‐workers is revised and recommended for practical application.
Heat transfer mechanisms in gas fluidized beds. Part 1: Maximum heat transfer coefficients
Authors: Melerus Otto , Mattmann Wolfgang 
Published: August 2005

AbstractThis contribution presents the prediction of maximum heat transfer coefficients in bubbling fluidized beds, which takes into account thermal and fluid‐dynamic properties of particulate material and fluidizing agent. The analysis suggests that heat transfer between heating or cooling surfaces and bubbling fluidized beds consists mainly in a particular manifestation of convective heat transfer. Another feature is an appropriate modelling of the particle convective component leading to a two‐phase Prandtl number.
A new fluorescence method for measuring cross‐fluctuation fo two non‐reactive components in a mixing device
Authors: André Christophe , David René , Villermaux Jacques , André Jean‐Claude 
Published: August 2005

AbstractA novel method for measuring local deviations from perfect mixing of two non‐reative tracers is presented. It is based on the partially quenched fluorescence of one fluorescent tracer by a second tracer. When the concentration fluctuations are small, the deviation from the linear behaviour yields the cross‐correlation of the fluctuating components of the concentrations of both traces from an – easy to record – average value of fluorescence intensity obtained in the focus of a laser beam. The method was proven to be suitable for measuring these quantities in a 1125 cm3 well‐stirred tank as a function of location and stirring speed.
Heat transfer and pressure drop in single rows of tubes in cross‐flow
Authors: Beziel Michael , Stephan Karl 
Published: August 2005

AbstractResults of experimental investigations on the influence of turbulence intensity and pitch‐to‐diameter ratio on heat transfer and pressure drop in single rows of plain tubes are presented. Vertically arranged tubes with 16 different pitch‐to‐diameter ratios between 1.26 and 5.73 were heated by saturated steam, condensing inside, and cooled outside by air in cross‐flow. The turbulence intensity in the entrance cross‐section was enhanced by means of different biplanar grids installed in the test section of a wind tunnel upstream of the single rows. The mean streamwise turbulence intensity behind the grids, measured with a constant temperature hot‐wire anemometer, varied between 0.8% and 38.8%. Reynolds numbers ranged from 4 × 103to 2 × 105. For single rows, the measurements show that the Nusselt number for a given turbulence intensity increases with increasing Reynolds number. In the investigated range of Reynolds numbers, the drag coefficient is only slightly influenced by the inlet turbulence intensity. The use of turbulence grids thus leads to higher efficiencies of heat exchangers.
Atomization of liquids and suspensions with hollow cone nozzles
Authors: Dahl Hans Detlef , Muschelknautz Edgar 
Published: August 2005

AbstractLarge centrifugal forces of rotational flow are used in hollow cone nozzles to form a thin liquid film in the outlet, which disintegrates into relatively small droplets. The flow in the nozzle can be calculated by means of simple physically meaningful balances, based on the cyclone theory. The influence of wall friction is taken into account via a wall friction coefficient which depends on the Reynolds number of the nozzle flow. The break‐up mechanism of the liquid film was investigated under the consideration of nozzle outlet velocity and film thickness as well as gas and liquid properties. With increasing velocity and film thickness, a transition from aerodynamic wave break‐up to turbulent atomization was observed to take place. Equations presented in this paper allow the calculation of mass flow rate, pressure drop and drop size distribution of hollow cone nozzles with any given geometry.
Measurement of radiation emitted from thin vaporizing liquid films for the calculation of surface temperature
Authors: Hahn Kai , Mewes Dieter 
Published: August 2005

AbstractEvaporation of liquid films, not subjected to motion, and with a starting thickness of 1 mm, was tested. Solvents dichloromethane and ethanol were used as liquids. Surface temperature during evaporation was measured in a non‐intrusive way using pyrometry. The employed pyrometer was calibrated against a black body radiant. Measurement accuracy in the region of the ambient temperature is 0.2 K. Since any principal stray radiation is always measured along with the thermal radiation emitting from the liquid film, the measurement results are at first distorted. A correction calculation is described. With this, the various proportions of stray radiation can be subsequently calculated. In order to do this, the dimensions of the test equipment and the spectral data of the evaporating solvents must be taken into account. The quantity of stray radiation depends mainly on the properties of the surface onto which the liquid film is applied, as well as on the spectral transmissivity of the liquid. This was measured for every tested liquid according to wavelength and layer thickness. Where the spectral transmissivity of a liquid is low, a correction calculation of the measured surface temperature is not necessary, while a high level of accuracy is still retained.
Heat transfer in gas fluidized beds. Part 2: Dependence of heat transfer on gas velocity
Authors: Molerus Otto , Mattmann Wolfgang 
Published: August 2005

AbstractPart 1 of this report investigated the effects of system properties on heat transfer between heating or cooling surfaces and bubbling fluidized beds. This investigation produced six correlations, which define the respective maximum heat transfer. The present contribution shows that the heat transfer depends on superficial gas velocity, with the relationship expressed in terms of a dimensionless excess gas velocity which defines the ratio of effective thermal conductivity by particle mixing to that of the fluidizing agent. Simple procedures for a reliable prediction of heat transfer in bubbling fluidized beds are presented.
Trajectories and impact velocities of grinding bodies in planetary ball mills
Authors: Raasch Jürgen 
Published: August 2005

AbstractThe motion of grinding bodies in conventional ball mills has been repeatedly investigated, both theoretically and experimentally. It is well‐known that, depending on mill filling and speed of rotation, different motion patterns occur and some of these patterns, especially that of cataracting, can be described by simplified theories. This contribution presents such a theory of the cataracting motion of grinding bodies in a planetary ball mill. An analytical method for the evaluation of trajectories is given which permits an iterative calculation of the time and impact location of the grinding bodies on mill shell or mill filling. This leads to the determination of the impact velocity of grinding bodies and its component normal to the mill shell. On the assumption that this component is decisive for the grinding effect, conditions for an optimal design of a planetary ball mill are deduced.
Catalytic cracking in presence of an aromatic addition
Authors: Oboho Esio O. , Oboho Svetlana P. 
Published: August 2005

AbstractFluidized bed catalytic cracking of vacuum gas oil fractions in the presence of extract from phenol purification of heavy lubricating oil fraction as an aromatic addition was investigated. Results show that, at the optimum concentration of the addition, coke formation on the catalyst decreases by 50 to 70% while the content of olefinic hydrocarbons in gasoline decreases, with a corresponding increase in the content of paraffin/naphthene hydrocarbons. The yield of gasoline increases, while its octane number increases by about two units.
Predicting mass transfer in packed columns
Authors: Billet Reinhard , Schultes Michael 
Published: August 2005

AbstractCountercurrent‐flow columns are widely used in production processes in the chemical industry and their application in ecological engineering is of increasing importance. A theoretical model is presented here that allows mass transfer to be described in terms of packing geometry and physical properties which influence the gas‐liquid or vapour‐liquid systems in absorption, desorption and rectification columns. The relationships derived from the model can be applied to all countercurrent‐flow columns, regardless of whether the packing has been dumped at random or arranged in a geometric pattern.
Increased surface tension of pretreated plastics investigated with a fully automatic device
Authors: Osterhold Michael , Armbruster Kornelia 
Published: August 2005

AbstractMeasurements of surface tension of flame‐, plasma‐ and UV‐treated PP‐EPDM samples show that all three methods of pretreatment significantly increase the surface tension. The flame or plasma pretreatment increases especially the polar element of surface tension while the UV‐treatment enhances the disperse element. The measurements were carried out with a new fully automatic unit for determining contact angles (AURAM).
Performance of the scaba 6SRGT agitator in mixing of simulated xanthan gum broths
Authors: Galindo Enrique , Nienow Alvin W. 
Published: August 2005

AbstractPower consumption under non‐aerated and aerated conditions was measured in a 0.45 m diameter tank containing a range of xanthan gum solutions, using the Scaba 6SRGT impeller. Well‐mixed caverns were measured in a transparent Carbopol solution. The data are compared with previous results obtained with a Rushton turbine in the range of Reynolds numbers, Re, between 1 and 2000. In each case, the non‐aerated power numbers were similarly related to Re except that the Po values of the Scaba 6SRGT were 3 to 4 times smaller. Under aerated conditions, the aeration rate does not affect the power number, Pog, with the actual value falling as a result of increasing xanthan concentration. The Pog/Po vs Re curve passes through a minimum which is lower at higher xanthan concentrations. At the same Reynolds number, the decline in power consumption of the Scaba agitator due to aeration is 20 to 50% smaller than that observed with a Rushton turbine. Well‐mixed cavern shapes and sizes are also very similar to those observed with Rushton turbines and can be predicted from equations available in literature. However, instabilities in torque could present a problem in broths containing xanthan in concentrations above 35 kg m–3. Nevertheless, the Scaba agitator offers an interesting retrofitting possibility for xanthan fermentation, which could lead to improved performance.
Fuzzy evaluation of large suspension mixing tanks
Authors: Medek Jaroslav , Hradecka Svatava , Dohnal Mirko 
Published: August 2005

AbstractAny process engineering scale‐up procedure is a source of uncertainties and risk. This paper presents an algorithm that completely eliminates the traditional scale‐up procedure using a direct application of “large‐scale” industrial knowledge. The large‐scale knowledge base is represented by fuzzy descriptions of 489 existing suspension mixing tanks. A fuzzy reasoning algorithm is used to answer different queries. Therefore, a flexible user‐computer dialogue is possible. A practical example is given in full detail.
Extended cyclone theory for gas flows with high solids concentrations
Authors: Trefz Michael , Muschelknautz Edgar 
Published: August 2005

AbstractLarge recirculation cyclones with high concentrations of particulate solids have gained considerable importance in the field of circulating fluidized bed technology. To calculate a combustion process, the influence of the cyclone on the circulating quantity of solids and their grain size distribution must be known. Measurements in a 105‐MW‐plant in 1989 showed that the existing cyclone theory was not sufficient for this purpose. In a laboratory cyclone (900 mm in diameter), the separation and classification of solids in a gas flow was investigated. The cyclone was fed from a fluidized bed and operated with cold air and quartz of various grain size distributions. Based on this experimental device and the theory of momentum transfer between solids and gas flow, a new, more accurate method of calculating the separation efficiency was developed.
A physical model for the prediction of liquid hold‐up in two‐phase countercurrent columns
Authors: Billet Reinhard , Schultes Michael 
Published: August 2005

AbstractThis contribution presents the determination of liquid hold‐up in gas/liquid two‐phase countercurrent columns filled with random or structured packings. The equations resulting from the established physical relationships are varified against the values for liquid hold‐up determined experimentally on 56 different column packings and 16 gas/liquid systems. The experimental and calculated results agree well, with only slight deviations. This also applies to the range between the loading and flooding points for two‐phase countercurrent flow.
Standardization of a newly designed vibrating capillary apparatus for the preparation of microcapsules
Authors: Ghosal Swapan Kumar , Talukdar Prasanta , Pal Tapan Kumar 
Published: August 2005

AbstractVibrating capillary apparatus (VCA) was designed and constructed for the preparation of sulphamethoxazole (SMZ) microcapsules using gelatin as a coating polymer. The microcapsules were characterized by physico‐chemical methods. The apparent diffusion coefficient Da and diffusion rate constant KBL of the drug were measured at pH of 1.2 and 7.2. Better controlled release products were obtained in the VCA.
Comparison of selected methods for downstream processing in the production of bacterial lipase
Authors: Wenzig Edda , Lingg Sabine , Kerzel Paul , Zeh Genovefa , Mersmann Alfons 
Published: August 2005

AbstractEnzymes are of growing interest to the chemical and pharmaceutical industries as highly specific biocatalysts. An obstacle to a large‐scale application of such proteins is the expenditure on recovery operations which can amount up to 80% of the total production costs. Therefore, it is necessary to investigate in detail the individual stages of downstream processing in order to obtain high product yields without loss of quality. After a survey of recovery operations and information on some special features of proteins which are relevant to downstream processing, this paper deals with the methods of precipitation, chromatography and foam fractionation. Several results obtained with a real, multicomponent system, namely the supernatant of lipase fermentation, are presented and compared with one another.
Comparison of cracking and hydrocraking of n‐heptane on H‐ZSM‐5 catalysts
Authors: Liers Joachim , Meusinger Josefin , Reschetilowski Wladimir 
Published: August 2005

AbstractAcid catalyzed cracking and bifunctional cracking of n‐heptane were investigated on HZSM‐5 catalysts. At a reaction temperature of 543 K, the cracking on metal‐free zeolite was found to be directly proportional to hydrogen partial pressure. Hydrogen influences the hydrogenation of product olefins and carbon deposits and therefore enhances the overall activity. Under the same conditions, in the presence of platinum, the hydrocracking rate reaches a maximum with increasing hydrogen partial pressure. The reaction can be formally described by a Langmuir Hinshewood mechanism: hydrogen is adsorbed on Pt in competition with hydrocarbons. The maximum reaction rate depends on a favourable ratio of the two adsorbed reactants. The energy of activation of hydrocracking was over 100 kJ/mol higher than that of acid cracking.
Kinetics of tetrachloroethene photochlorination in a homogeneous system
Authors: Miller Jacek S. , Nowicki Lech , Ledakowicz Stanislaw 
Published: August 2005

AbstractThe mechanism of free‐radical chain reaction of tetrachloroethene photochlorination in a homogeneous liquid system is discussed and three kinetic models based on the reaction mechanism are presented. The parameters of these three models have been evaluated on the basis of experimental data presented in [1].
Swelling phenomena of emulsion liquid membranes with dithio‐DEHPA as carrier
Authors: Reis M. Teresa A. , Carvalho Jorge M. R. 
Published: August 2005

AbstractThe purpose of this paper is to investigate the swelling of emulsion liquid membranes using dithio‐DEHPA as carrier. The application of interest was the removal of zinc from a synthetic aqueous solution which simulates a zinc plant effluent. The effect of several variables such as the concentration of carrier in the membrane, stirring speed and permeation time on the swelling of the emulsion is reported. Experimental results show that occlusion depends mainly on the amount of carrier in the membrane and can be significant when the concentration of carrier is lower than 6.0%. The interfacial tension analysis confirms that the size of globules is influenced by the concentration of carrier in the membrane. Stirring speed and permeation time are related to the water transport and must be kept at low values.
Determination of overall mass transfer coefficients in fixed bed sorption columns
Authors: Özdural Ahmet R. 
Published: August 2005

AbstractIn this study, a simple and effective technique for determining overall mass transfer coefficients in fixed bed sorption columns with recycle is presented. This new technique is free of the assumption of negligible time rate of solute concentration change in the fluid, i.e. (∂c/∂t) = 0, which has been widely used in former fixed bed sorption column analyses.