bluuebunny/crossref_metadata_2025_split huggingface dataset:
The pressure ratio of critical two‐phase flows
Authors: Hardekopf Friedhelm , Mewes Dieter 
Published: August 2005

AbstractDepressurization of a pressure vessel, containing a liquid or a gas is limited by the maximum possible mass flux. This flux occurs at a certain drop in pressure. The ratio of ambient pressure to that inside the vessel must be less than a certain critical value. The critical pressure ratio depends on the thermodynamic state of the fluid inside the vessel and on the geometry of the outlet cross‐section. The outlet can be a pipeline, a safety valve or a rupture disk. The results of known theoretical and experimental work are presented. In previous experiments, saturated liquids, two‐phase flows or pure vapours were examined. In order to predict the critical pressure ratio, certain assumptions are necessary. These are derived for three well‐defined cross‐sections of the vessel outlet.
Effects of pretreatments on semi‐continuous anaerobic digestion of wheat straw
Authors: Tosun Ayşe , Selçuk Nevin , Soyupak Selçuk 
Published: August 2005

AbstractThe effects of alkali treatment, nitrogen supplement and hydraulic retention time on methane production rate from semi‐continuous anaerobic digestion of 5% wheat straw‐water mixtures were investigated. The experiments were carried out in laboratory scale fermenters, fed with 1 1 of basic, alkali treated and nitrogen supplemented 5% wheat straw‐water mixtures, respectively, and maintained at 55 °C. Digestion experiments were performed for hydraulic retention times of 8, 10 and 15 days. The amount and composition of produced gas were measured until steady state was attained in each run. The steady‐state methane production rates were found to increase with hydraulic retention time and with the type of slurry in the following order; basic, nitrogen supplemented and alkali treated slurry. Data obtained from the experiments were employed to determine the kinetics of methane production from anaerobic digestion of wheat straw, for the assessment of pretreatment effects on process kinetics. The predicted methane production rates were found to be in a reasonably good agreement with the measurements.
A new model of the effect of stirring intensity on the rate of secondary nucleation
Authors: Ploß Reinhard , Mersmann Alfons 
Published: August 2005

AbstractSecondary nucleation in industrial crystallizers depends on both supersaturation and mechanical stress by stirring. Most models which consider mechanical stress assume that nucleation is proprotional to the energy transferred to the crystals during collisions. This is not based on any physical relationship and, in addition, the models do not satisfactorily reproduce the experimental results. Own model, based on the theory of Hertz/Huber, which accounts for the stress of the crystals caused by impact, gave better results. This well‐known and proven theory allows the calculation of the volume abraded during collisions between crystals and stirrer or walls. Introducing a nucleate efficienncy, the effect of mechanical stress on the rate of secondary nucleation, due to stirring intensity and crystallizer size, can be determined.
A new particle size effect
Authors: Kral Hans 
Published: August 2005

AbstractThe sintering effect of highly dispersed metals is the reason for the following phenomena: thermal deactivation, particle size effect, separable or non‐separable kinetics and the isokinetic relationship ( = compensation effect). A comparison of these phenomena reveals a contradiction which can be reconciled by a new particle size effect. This effect is characterized in the following way: The dependence of specific activity on particle size is always connected with a variation of the activation energy, caused by the particle size distribution. Therefore, this effect is referred to as the partical size and distribution effect, P.S.D.E. This new concept describes all the observed phenomena of the conventional partical size effect. Moreover, it is consistent with similar effects such as non‐separable kinetics and the isokinetic relationship. In consequence, the method of isothermal measurement of specific activity is inadequate.
Reduction of energy requirements in distillation
Authors: Stichlmair Johann , Stemmer Ansgar 
Published: August 2005

AbstractDistillation has been, up to now, the standard method for separating fluid mixtures in the process industry and the consensus is that it will remain so for years to come. The only disadvantage of distillation is its high energy requirement. In the following, it will be demonstrated on the example of an ideal ternary mixture, how the energy requirement of distillation process can be reduced. Very effective are some modifications of single columns, optimization of column sequences and direct or indirect column coupling. It will be shown that, just by column coupling, the energy requirement can be reduced to a third.
Venturi scrubber calculation and optimization
Authors: Haller Heinz , Muschelknautz Edgar , Schultz Tilman 
Published: August 2005

AbstractCollection efficiency and pressure loss of a venturi scrubber can usually be determined from the calculation models of Barth and Calvert. However, this only leads to reasonable results if the droplets are uniformly distributed throughout each cross‐section of the washing zone. In this work, a two‐zone models is developed which allows the calculation of the venturi scrubber at operating conditions with a non‐uniform droplet distribution. The scrubber geometry is also taken into account. A venturi scrubber was developed on the basis of this new model. Its energy consumption is significantly lower than the well‐Known optimum characteristic of Wicke and Holzer. For ideal operating conditions, a new optimum characteristic is given which should be the aim of future optimizations.
Mass transfer and chemical reaction in fluid two‐phase systems
Authors: Langemann Horst , Brandt Hermann , Neumann Martin , Wüllner Gerhard , Voigt Markus 
Published: August 2005

AbstractSteady‐state concentrations of the transferred reactant in the bulk phase and the non‐flowing diffusion boundary layer of an isothermal, isobaric two‐phase reactor with an irreversible first‐order reaction and constant composition of one phase.
Measurement of aeration capacity of fermenters
Authors: Linek Václav , Beneš P. , Vacek Václav 
Published: August 2005

AbstractImportant 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

AbstractThe 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

AbstractHeat 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

AbstractAn 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

AbstractTo 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

AbstractThe 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

AbstractContinuous 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

AbstractLiquid‐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

AbstractMean 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

AbstractCrystallizer 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

AbstractThis 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

AbstractModelling 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

AbstractIn 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

AbstractThe 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

AbstractThe 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

AbstractFormaldehyde 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

AbstractCopper 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

AbstractExperimental 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

AbstractThe 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

AbstractA 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

AbstractA 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.