bluuebunny/crossref_metadata_2025 huggingface dataset:
Advances in modelling and design of multitubular fixed‐ bed reactors
Authors: Stankiewicz Andrzej
Published: August 2005

Starting from the review of current industrial designs, the present paper analyzes thermal interaction between reactants and coolant in multitubular fixed‐bed reactors. The interaction can be described quantitatively in terms of parameters characterizing transport processes both on the tube side and in the intertubular space. The study provides a detailed discussion of existing methods and correlations used for the evaluation of these parameters. The methods presented here can be considered as a basis for the development of a more comprehensive approach to the modeling and design of multitubular catalytic reactors.
Thermally stabilized combustion
Authors: Churchill Stuart W.
Published: August 2005

Thermally stabilized combustion has a number of unique characteristics which permit the generation of steam or other forms of process energy from the heat of combustion of a gaseous or clean liquid fuel in remarkably compact, integrated apparatus while truly minimizing the concentrations of NOx, CO and unburnt fuel in the effluent. These characteristics, which have been identified by a long‐range program of research, are described and the advantages and limitations of this process are discussed.
Fluid dynamic description of jet‐loop reactors in multiphase operation
Authors: Tebel Karl Heinz , Zehner Peter
Published: August 2005

A superposition of simple physical equations allows a satisfactory, comprehensive fluid dynamic description of jet‐loop reactors in multiphase operation up to a dispersed phase hold‐up of 15%. In the case of higher concentrations, there are further interactions which are not yet included in the model description. Apart from the drag coefficient of the single‐phase jet loop, information on the particle swarm behaviour, i.e. on the slip velocity of the dispersed phase is required. Explicit formulation of the influence of the relevant geometrical parameters permits a reliable scale‐up without additional adaptation parameters.
Vapour‐liquid equilibria of hydrogen/coal liquid and methane/coal liquid systems at elevated temperatures and pressures
Authors: Wiegand Karl W. , Strobel Bernd O. , Hofmann Hanns
Published: August 2005

A cubic equation of state is modified in such a way that prediction of PVT data from 40 model compounds, typical of coal oil, becomes possible with an absolute mean deviation of less than 2% for saturated liquid volumes and vapour pressures > 1 bar. Additional correlations for binary interaction parameters are obtained by an optimization procedure using vapour‐liquid euilibrium (VLE) data from known heavy hydrocarbon liquid/light gas systems. When the modified equation is applied to coal‐derived liquids, only specific gravity and boiling analysis data of the coal liquids are required, primarily in order to determine the equation‐of‐state parameters. The proposed equation is shown to allow a good prediction of VLE data for systems consisting of wide‐boiling‐range coal oils and light gases. Experimental values were obtained at elevated temperatures and pressures with a circulation flow apparatus.
A new load cell for measuring normal and shear stresses
Authors: Schulze Dietmar , Lyle Christopher , Schwedes Jörg
Published: August 2005

A special stress measuring device for determining the normal and shear stresses acting on silo walls was developed and tested. The load cell can be used for measuring simultaneously the normal stress as well as the intensity and direction of the shear stress.
Directional specific shear‐rate measurements in gas‐liquid two‐phase flow
Authors: Pauli Judith , Menzel Thomas , Onken Ulfert
Published: August 2005

Wall shear rate vectors in a bubble column and an airlift‐loop reactor were measured using the limiting‐current electrodiffusion technique. In connection with a new circular three‐segment probe, the magnitudes and directions of shear rates were determined. The results for the bubble column are in good agreement with hot film‐anemometry measurements in the same column. Moreover, the spiral flow structure, postulated in the shear‐zone model of Franz, has been confirmed. In addition, the measuring technique was used to determine the flow structure in an airlift‐loop reactor employed for the cultivation of animal cells. The region above the gas distributor of this fermenter has been identified as critical for mechanical damage to the cells.
Measurement of heat transfer coefficients in tubes by temperature oscillation analysis
Authors: Roetzel Wilfried
Published: August 2005

An experimental technique and evaluation method is described for the determination of local heat transfer coefficients in tubes or other ducts. By means of a rotary mixing valve, cold and warm fluid flows are mixed in order to generate an arbitrarily shaped but periodically oscillating inlet temperature profile at the test tube. The propagation of the fundamental harmonic oscillation from the fluid to the outer surface of the tube wall is calculated analytically. Comparison of fluid and wall oscillations yields the heat transfer coefficient to be measured. The inaccurate measurement of fluid bulk temperature in the centre of the cross‐section is compensated by an additional correction. Experiments were carried out with turbulent water flow through a copper tube. Measured heat transfer coefficients were compared to values calculated using Hausen's equation and good agreement was obtained.
Investigation of a wet dust scrubber with a pneumatic nozzle: Dust collection based on turbulent diffusion
Authors: Centner Peter , Büttner Helmut , Ebert Fritz
Published: August 2005

The “nozzle scrubber” is a wet scrubber in which the scrubbing water is dispersed in dust laden gas stream by means of one or more pneumatic nozzle. This scrubber is distinguished by an excellent collection efficiency for submicron dust at an unusually low energy and water consumption. So far, the physical effects affecting the separation cannot be explained by a well‐defined theory. Therefore, it is sensible to investigate the collection efficiency with regard to the mechanisms of inertial impaction, turbulent diffusion and coalescence induced by turbulence. The experimental equipment is of a very simple design. A light scattering device was used to measure the particle distributions. In addition, electron micrographs were analyzed to obtain information about the submicron particles. The influence of operating parameters on grade efficiency has been demonstrated by their systematic variation. The contribution of turbulent diffusion to the collection efficiency has been confirmed; nevertheless, grade efficiencies were also measured when inertial impaction prevailed.
Influence of feed solids concentration on the performance of hydrocyclones
Authors: Braun Thomas , Bohnet Matthias
Published: August 2005

Even though the influence of solids concentration in the feed on the separation efficiency of hydrocyclones has long been recognized, a systematic research on the change in pressure drop across the hydrocyclone and the latter's separation characteristics has thus far been lacking. If all other operating parameters are kept constant, an increase in feed concentration generally leads to a coarser cut size, reduced sharpness of separation and a rise in pressure drop. Apart from the particles hindering one another's radial motion, the limited capacity of the apex valve and the changes in the flow field within the hydrocyclone cause additional particles to be entrained by the overflow. The flow ratio thus becomes an additional parameter in determining the cyclone efficiency. A theoretical model, which takes these effects into account, has been developed and successfully tested against experimental data.
Modern carbon fibres from polyacrylonitrile (PAN)‐polyheteroaromatics with preferred orientation
Authors: Fitzer Erich , Frohs Wilhelm
Published: August 2005

This contribution presents the mechanical data of high performance carbon fibres currently available on the market, based on experimental studies on stabilization and pyrolysis of PAN (SAF) from Courtaulds. The effects of stabilization and carbonization temperatures on the properties as well as on the ultra‐ and crystalline structures of the fibres are shown in more detail.
Modelling of thermal desorption of active coke loaded with sulphuric acid and ammonium sulphate
Authors: Richter Ekkehard
Published: August 2005

The BF‐Uhde‐Mitsui Process uses active coke for SO2‐ and NOx‐removal from flue gases in the temperature range between 100 and 190 °C, Experimental methods of thermal regeneration were applied to the evaluation of the state of the adsorbent after use in flue gas cleaning and of the parameters for disrober design. A reaction model was derived from experiments carried out in differential and back‐mix reactors. The parameters were evaluated by adaptation of the model to the adsorption spectra. The model was successfully applied to the regeneration of active coke in a fluidized bed reactor.
Mass transfer in countercurrent and cocurrent bubble columns
Authors: Seno Tadachika , Uchida Shigeo , Tsuyutani Shinji
Published: August 2005

The hydrodynamic and mass transfer characteristics in countercurrent, cocurrent and liquid batch operations with various Newtonian liquids were studied experimentally using the same bubble column. Taking the effect of gas sparger geometries, operating variables and liquid properties into account, empirical correlations were obtained for the gas hold‐up and the volumetric liquid‐phase mass transfer coefficient.
Study on dynamic behaviour of thermally coupled distillation processes
Authors: Xien Xu , Chunyan Wang
Published: August 2005

A dynamic mathematical model has been developed which is suitable for thermally coupled distillation processes. An algorithm known as the equation‐decoupled method was used for simulation. EPISODE software and LU decomposition method were adopted to solve the ordinary differential and algebraic equations of the model, respectively. The initial conditions, viz. a solution for the steady state of the process in dynamics simulation were obtained by means of modified Naphtali‐Sandholm algorithm. Research on the dynamic behaviour of thermally coupled distillation processes was carried out on two examples. It was found, via the dynamic simulation, that a disturbance in the distribution of vapour coupled stream has a large effect on the composition of vapour side withdrawal and, similarly, for liquid coupled stream, on that of liquid side withdrawal when the fraction of side withdrawal is fixed, and a smaller effect when the quantity of side withdrawal is fixed.
Formation of Di‐isobutene, main by‐product of methyl tertiary butyl ethyl ether synthesis catalyzed by ion exchange resin
Authors: Rehfinger Alwin , Hoffmann Ulrich
Published: August 2005

An experimental set‐up is presented for the measurement of steady‐state reaction rates in the liquid phase methyl tertiary butyl ether (MTBE) synthesis from isobutene and methanol using ion exchange resin as catalyst. This apparatus was used for a separate investigation of the main side reaction, i.e., the formation of isobutene dimers (DIB), in the temperature range between 60 and 90°C. The reaction catalyzed by Amberlyst 15 (A15) showed no steady‐state behaviour, but the catalytic activity declined at a rate dependent on the reaction conditions. Time constants for activity loss were determined in the range from 3.5 to 30 h. The deactivated A15 catalyst could be regenerated through MTBE synthesis experiment. Deactivation is assumed to be caused by blocking of the microparticle gel phase by higher isobutene oligomers. The DIB formation, using 1‐butene as solvent, was of 2nd order with respect to isobutene and showed an apparent activation energy of about 40 kJ/mol.
Determination of flooding gas velocity and liquid hold‐up at flooding in packed columns for gas/liquid systems
Authors: Maćkowiak Jerzy
Published: August 2005

A new model of suspended bed of droplets for describing the vaour or gas the vapour or gas velocity at the flooding point in packed of columns for rectification and absorption under vacuum and normal pressure is presented metallic, ceramic and plastic packings with diameters of 8–90 mm as well on sheet metal and gauze packings, in a wide range of liquid and vapour loads. Approximately 650 literature measurements and own data were evaluated. The mean relative error in determining the gas velocity at flooding point is less than ±5%. On the basis of the double layer model, a new equation was derived for the hold‐up at flooding point, which is needed for the calculation of the flooding gas velocity. An example of calculations for sample applications is also included.
Agitation of aerated emulsions
Authors: Schneider Torsten , Vettermann Rainer , Franz Kristian
Published: August 2005

Aerated emulsions are gaining significance in fermentation as well as in inorganic and organic chemistry. In these processes, liquid‐liquid mass transfer can be the limiting step. Therefore, the effect of gassing rate on droplet size was investigated as a function of dispersed liquid phase concentration and power input in different vessels. At high power inputs, the droplet size decreased. With increasing dispersed phase concentration and gassing rate, the droplet size increased and its dependence on power input subsided.
Batch cooling crystallization at constant supersaturation: Technique and experimental results
Authors: Gutwald Thomas , Mersmann Alfons
Published: August 2005

A new laboratory plant for batch cooling crystallization is described, which allows to maintain the supersaturation at a constant level during an experimental run. A method for continuous supersaturation measurements has been developed, using a density meter and a hydrocyclone. Experimental results obtained from a seeded solution in constant supersaturation cooling mode and at constant cooling rate are compared. In the case of a constant cooling rate, the supersaturation passes through a sharp maximum, whereby effective nucleation is enhanced. As a consequence, a smaller median crystal size is obtained than for cooling at constant supersaturation. Equation for controlled cooling at a constant supersaturation require an accurate description of the effective rate of nucleation. Therefore, the mechanical stress, to which the crystals are subjected, must be included as the main source of new nuclei. This is shown by the influence of stirrer on batch time.
Simple new formulae for efficiency and mean temperature difference in heat echangers
Authors: Martin Holger
Published: August 2005

The well‐known formulae for efficiency and mean temperature difference of a heat exchanger as functions of its numbers of transfer units, or dimensionless lengths, can be written in a more compact form by introducing the auxiliary function φ(x) = x/(1 – e−x). The resulting new formulae show a number of advantages: They are shorter, easier to memorize, and in many cases the limiting values can be seen more directly. They may therefore contribute to easier and faster heat exchanger design, and to reduced probability of errors in the relevant calculations.
Thermal decomposition of 2, 3‐dimethyl butane: Experiments and mechanistic modelling
Authors: Stabel Uwe , Hönig Ulrich F. , Nowak Ulrich , Ederer Hanns J. , Ebert Klaus H.
Published: August 2005

Pyrolysis of 2,3‐dimethyl butane (DMB) was carried out in a quartz flow reactor in the temperature range from 740 to 1032 K at normal pressure. The input concentration of DMB was 3.3 × 10−3 mol/1 using argon as diluent. Reaction time ranged between 3.1 and 3.9 s. The following products were analyzed by two‐column gas chromatography: hydrogen, methane, ethene, propane, propene, butenes, butadiene, 2‐methyl‐2‐butene, isoprene, benzene and toluene. Compared to thermal decomposition of n‐hexane under similar experimental conditions, the main difference concerned the formation of ethylene, ethane and branched alkanes. A reaction model, based on elementary reactions, was developed to predict the experimental results and to verify our data basis of elementary reactions under different conditions. The model gives a quantitative description of the complex chemistry of the process. In addition, an algorithm is presented for model reduction.
Sensitivity analysis of catalytic conversion of n‐C6
Authors: Wolff Andrzej
Published: August 2005

The present paper is a case study of an application of sensitivity analysis in chemical kinetics. Emphasis is laid upon chemical interpretation of sensitivity information and on identification of the most important model important model parameters. The kinetic model for reforming of C6 hydrocarbons proposed by Mobil [14] is extended to the analysis of the behavior of n‐hexane conversion in an adiabatic reactor. The importance of six initial conditions (feed composition and initial temperature) is analyzed by the computation of normalized first order sensitivity gradients (y/y) (δyi/δy). The relative importance of 21 model parameters αj is estimated by the computation of normalized sensitivity gradients of the type (αj/yi) (δyi/δαj). The influence of the decisive model parameters ΔH and ΔH (activation enthalpies of benzene hydrogenation and methyl cyclopentane isomerization, respectively) as well as operating parameters is presented. The problem of uncertainly in the value of ΔH and its influence on the model solution is also sown. Finally, some advantages of the application of normalized gradients of the explanation of process behavior are discussed.
The implications of carboxylic acid properties
Authors: Andereya Erwin , Chase J. David
Published: August 2005

Some properties of carboxylic acids are reviewed, with emphasis on recent experimental data, Qualified, consistent latent heat of vaporization data were developed for the series and a two‐population viewpoint is suggested. The equation of state formulated by Grenzheuser [1] is also recommended as a practical tool, and its further development is urged.
Adsorption and catalytic reactions of NO and NH3 on activated carbon
Authors: Richter Ekkehard , Schmidt Hans‐Jürgen , Schecker Hans‐Georg
Published: August 2005

In industrial processes, the reduction of nitrogen oxides by ammonia on activated carbons is carried out at temperatures between 90 and 190 °C. Adsorption of NO and NH3 on the catalyst was investigated separately. Reactions models for NO‐reduction by carbon and ammonia were derived from experiments carried out in an integral reactor. In each case, the formation of an adsorbed (NO2)‐complex is an important step. The kinetics of both reactions was described by modified Langmuir‐Hinshelwood equations.
Mixing in continuous DTB and FC crystallizers
Authors: Gupta Bhaskar Sen , Dutta Tapas K.
Published: August 2005

Owing to imperfect mixing, the theoretical prediction of CSD for an MSMPR crystallizer deviates from the experimental results. In the present work, different modelling approaches were adopted to account for incomplete mixing in DTB and FC crystallizers. For DTB crystallizers, compartmental model, based on an earlier work of Nyvlt et al. has been proposed. For FC crystallizers, a mixed model comprising perfectly mixed and plug flow regimes has been put forward. This is based on the tracer response studies reported by de Jong. Predicted results were compared with experimental data of Bennett and van Buren for continuous urea crystallizers.
Selection and design of aerobic bioreactors
Authors: Mersmann Alfons , Schneider Georg , Voit Harald , Wenzig Edda
Published: August 2005

Compared to chemical reactors, there are additional requirements to be considered when selecting and designing a bioreactor. The cultivated organisms and most of the desired products are to a greater or lesser extent sensitive to temperature, pH and Shear stress. Furthermore, sterilization often plays an important role in maintaining a monoseptic process. Many design procedures for chemical reactors can be applied but requirements which are relevant to the biological system are sometimes decisive. Consequently, it is useful to first consider the essential features of the organisms with respect to the selection and design of bioreactors. Attention must be paid to the fermentation medium because its flow behaviour can range from slightly viscous and Newtonian to highly viscous, non‐Newtonian. Many papers deal with low viscosity fermentation broths [1–5]. However, little is known about the design of bioreactors for highly viscous non‐Newtonian liquids. Fundamentals for the design of bioreactors are presented. It has been attempted to apply theoretical equations suitable for both, low viscosity Newtonian and high viscosity non‐Newtonian fermentation broths. Apart from the calculation procedure for the OTR‐values, the difference between global and local values within bioreactor is demonstrated by means of velocity and shear stress profiles. Special requirements for bioreactors such as prevention of excessive foaming, shear sensitivity of micro‐organisms and cell‐lines and effective sterilization are also discussed.
Collection of fine adhesive and cohesive dusts with pluse‐jet fabric filers
Authors: Schmidt Eberhard , Löffler Friedrich
Published: August 2005

The collection of reactive and therefore extremely adhesive and cohesive fine particles (< 1 μm) by means of bag filters with pulse‐jet cleaning may present problems. The electron‐beam dry scrubbing (EBDS) process, used to remove SO2 and Nox in a power plant of the Badenwerk AG, Karlsruhe, serves as an example. To solve the occurring problems and achieve a satisfactory filter performance, extensive know‐how of process engineering is necessary. This contribution deal with the following aspects: construction of the cleaning system, selection of filter medium, precoating, and dosage of an auxiliary dust during filtration.
Fluid dynamics of pulsed sieve plate extraction columns
Authors: Lorenz Markus , Haverland Hartmut , Vogelphol Alfons
Published: August 2005

The presented contribution reports on comprehensive hydrodynamic investigations in two pulsed sieve‐plate extraction columns (PSE) on a pilot scale. The experiments were conducted with three different sieve plate geometries employing test systems recommended by EFCE, under varying pulsation conditions and throughputs. The results of the investigation add to the existing knowledge of relationships between hydrodynamic parameters, drop size, hold‐up, flooding throughput and mixing and operating parameters. They also provide useful information for scale up, selection of sieve‐plate geometry, most favorable operating range, and constructive design of equipment. On the basis of measurements, analytical methods are recommended for prediction of PSE hydrodynamics.
Effect of mixing behaviour on gas‐liquid mass transfer in highly viscous, stirred non‐newtonian liquids
Authors: Henzler Hans‐Jürgen , Obernosterer Gerd
Published: August 2005

When declaring and using process engineering data such as, for exmple, mixing times or kLa values, it is assumed that these apply to the entire reactor contents. The condition of uniform mixing, necessary for this, is generally met in the regime of turbulent flow. When highly viscous and, above all, strongly non‐Newtonian liquids are stirred in small reactors, there are frequently also regions of laminar flow and completely stagnant zones, which are only partially mixed or not at all. The present paper pursues the question to what extent is the gas‐liquid mass transfer in stirred, highly non‐Newtonian liquids influenced by the mixing behaviour of the reactor. The results show that, below certain Reynolds numbers, three relatively distinct regions exist, with different mixing intensities. Between an almost ideally mixed region in the vicinity of the stirrer and a completely stagnant and dead one, there is a zone of very slight motion. This finding demonstrates that the usual determination of integral or volume‐based data in the literature is neither logical nor adequate for the case under consideration. Thus, the gas‐liquid mass transfer takes place mainly in the relatively well mixed region. Therefore, use of a kLa value also requires the volume of this region to be declared. Only the knowledge of this volume enables us to correlate the kLa values in such a way that the sorption characteristics thus obtained appear suitable for scale‐up. This procedure, which is illustrated by numerous examples of measured results for different stirrers, is important whenever design data for highly viscous liquids are to be worked out on the basis of laboratory measurements. Only when larger equipment is used, in which turbulent flow can be achieved, this problem does not arise because of the relatively uniform mixing of reactor contents.
Fluid mechanics of circulating fluidized beds
Authors: Wirth Karl‐Ernst
Published: August 2005

A 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

The 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

This 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

Fluidized 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

Power 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

The 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

This 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

A 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

Results 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

Large 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

Evaporation 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

Part 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

The 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

Fluidized 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

Countercurrent‐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

Measurements 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).
Temperature oscillation technique for determination of local convective heat transfer coefficients without fluid temperature measurement
Authors: Roetzel Wilfried , Prinzen Stephan , Wandelt Michael
Published: August 2005

A new experimental technique with periodic laser heating is described and applied to the measurement of local heat transfer coefficients at the inner surface of an agitated vessel. Only radiative surface temperature measurements on the outer wall of the vessel are necessary.
Performance of the scaba 6SRGT agitator in mixing of simulated xanthan gum broths
Authors: Galindo Enrique , Nienow Alvin W.
Published: August 2005

Power 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

Any 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

Large 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

This 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

Vibrating 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

Enzymes 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

Acid 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

The 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

The 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

In 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.