bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new method for the prediction of liquid pulsed sieve‐tray extractors
Authors: Pietzsch Wolfgang , Blass Eckhart 
Published: August 2005

AbstractAs a part of a research project on the mass transfer in liquid pulsed sieve‐tray extraction columns (PSE), the diameters and hold‐ups of the drops were measured: the drop size using a suction technique, with photoelectric detection, which was adapted to the special boundary conditions of the PSE; the integral hold‐up by the pressure difference between the lower and upper parts of the column. Since experimental results cannot be described by known calculation formulae for the Sauter mean diameter and the hold‐up, a new method of calculation was developed. It is phenomenologically based on high‐speed photographs of the drop motion on a sieve tray. The mathematical‐physical model allows the prediction of drop size and hold‐up within certain limits, while the possible different operating regimes of the PSE, i.e. the mixer‐settler and dispersion regimes can also be estimated.
Distillation columns with vertical partitions
Authors: Kaibel Gerd 
Published: August 2005

AbstractDistillation columns with vertical partitions can separate a feed mixture into 3 or 4 pure fractions. Compared to other column arrangements, their investment costs and energy consumption are lower. Production columns show good results and are easily controlled. Conventional distillation columns produce only 2 pure product streams at the top and at the bottom of the column. Side products are contaminated by light or heavy components, depending on the location of the side stream in the rectifying or stripping section. This disadvantage is set aside by using a distillation column with a vertical partition. The internal separation wall prevents lateral mixing of liquid and vapour in the central part of the column, forming there separate feed and outlet sections. In the presence of a vertical partition, 3 or 4 pure fractions can be obtained in a single distillation step. This is particularly advantageous when heat sensitive components are to be separated. On account of good thermodynamic properties, the energy consumption is 20 to 35% lower than that of other distillation arrangements. The control behaviour is similar or better than that of conventional distillation columns.
Fouling of heat transfer surfaces
Authors: Bohnet Matthias 
Published: August 2005

AbstractFouling and/or scaling of heat transfer surfaces causes serious problems in industry. Prevention of fouling is therefore essential for technical (considerable deterioration of heat transfer) and also economic reasons (increased costs). In order to provide successful countermeasures, it is, however, necessary to obtain more detailed information on the physical, chemical and biological processes which produce fouling. Based on the already known fouling mechanisms, it is shown that a satisfactory prediction of fouling behaviour of heat exchangers is not yet possible. This contribution presents a physical model for the description of fouling, caused by sedimentation and crystallization. It is assumed that, during fouling, deposition and removal processes overlap. In order to verify the theoretical considerations, experiments were carried out on a test rig, which could also be used for field experiments. Aqueous CaSO4 solutions served as experimental liquids. A comparison of experimental and calculated fouling factors shows a satisfactory agreement.
Computer‐aided design of tube‐bundle heat exchangers
Authors: Rümmer Peter 
Published: August 2005

AbstractBased on a paper by Hein, a dimensioning program for tube‐bundle heat exchangers with straight tubes and fixed tube sheets has been developed. The equipment to be dimensioned is tested at 14 critical points, with regard to permissible stresses. The optimum thickness of the tube sheet, the shell and channel are subsequently selected on the basis of economic criteria. Compared to dimensioning according to AD‐data sheet, it is possible to save between 10 and 25% of production costs. With the aid of a finite‐element (FE) program, complex structures such as heat exchangers can be calculated accurately. Several mesh‐generation programs were written for the data input. The structure of a tube‐bundle heat exchanger with straight tubes is generated with 3/D elements with only some geometrical data. An FE‐calculation of a heat exchanger is explained with the aid of an example and stress analysis is presented.
Microbial desulphurization of coal – development and application of a slurry reactor
Authors: Höne Hans‐Jürgen , Beyer Michael , Ebner Hans G. , Klein Jürgen , Jüntgen Harald 
Published: August 2005

AbstractMicrobial desulphurization of coal by pyrite oxidizing enrichment cultures containing predominantly Thiobacillus ferrooxidans was performed in an air‐agitated slurry reactor, 20 l in volume. A model of microbiological and chemical reactions, occurring at various points within the coal, was set up taking into account the pore structure of the coal. The influence of parameters relevant to industrial processes, such as superficial gas velocity, particle size, initial pyrite concentration, and slurry density of the coal, on the conversion of pyrite was examined. Variation of the superficial gas velocity in the range of 0.01 to 0.04 m/s confirmed that the reaction is not controlled by oxygen transfer from gaseous to liquid phase. The rate of pyrite oxidation depends mainly on the accessibility of pyrite to micro‐organisms which is determined by the particle size of the coal as well as the distribution of pyrite crystals in the coal matrix. The accessibility of pyrite to the micro‐organisms is described by the ratio of effective to maximum microbial activity, measured as oxygen consumption. Starting with higher initial concentration of pyrite in the coal increases the oxidation rate, according to first order kinetics. Enhanced slurry densities lead to a decrease of pyrite conversion, in spite of higher pyrite concentration. The maximum pyrite oxidation rate was measured at 15% (v/v) slurry density and 25°C as 1800 mg Spyr/kg coal per day, or 360 mg Spyr/l reactor volume per day.
Gas/liquid interfacial area per unit volume and volumetric mass transfer coefficient in stirred slurry reactors
Authors: Schmitz Michael , Steiff Artur , Weinspach Paul‐Michael 
Published: August 2005

AbstractIn three‐phase systems, where the liquid constitutes the continuous phase, solid is the catalyst and gas represents the dispersed phase, there are decisive criteria which have to be observed in reactor design. These are e.g. the interfacial area per unit volume between gas and liquid, the volumetric mass transfer coefficient and the mass transfer coefficient. The basic aim of the present work was therefore the investigation of these parameters in relation to the main influencing parameters. Process parameters stirrer speed and superficial gas velocity were varied as well as the physical properties such as liquid viscosity, solids concentration, particle diameter and a geometrical parameter, i.e. reactor diameter. The sulphite method was employed for the determination of these values. The test results confirmed the known relationships of power consumption and superficial gas velocity. An increase in the liquid viscosity leads to a decrease in all the tested values. In most cases, suspended solid particles lead to a lowering of the test values. The influence of the tank diameter on the plots of the test values against specific power consumption turned out to be invariant so that a scale‐up of geometrically similar systems can be carried out at constant power consumption, superficial gas velocity and liquid viscosity.
Desorption delay in gas/liquid systems during vessel top venting
Authors: Friedel Lutz 
Published: August 2005

AbstractDuring the sudden unheated vessel top venting of initially saturated two‐component gas/liquid mixtures, in which the gas is also extensively dissolved in the non‐evaporating liquid phase, a solubility inequilibrium develops between the phases; re‐equilibration can set in only after a so‐called desorption delay time. Laboratory measurements of this delay time were under‐taken with model mixtures of CO2 and water and viscous aqueous (Newtonian) solutions by high speed cinematography. The parameters of the experiments are relief cross‐section, initial liquid level, pressure, temperature, and concentration. The shortest deley time obtained lasts approximately 75 ms. It differs substantially from the minimum boiling delay time previously measured with various refrigerants in the same test facility. The experimental results are correlated by a semi‐empirical dimensionless power relationship, which includes all independent primary design variables generally availble in a physically consistent interrelationship. Reasonable extrapolations to other test conditions and aqueous two‐component systems with an acceptable accuracy systems can therefore be expected.
Pressure drop and flooding in packed columns operating at high pressures
Authors: Krehenwinkel Helmut , Knapp Helmut 
Published: August 2005

AbstractCorrelations for pressure drop and upper capacity limit (flooding) are useful for the design of packed columns. Available correlations are based on the results of measurements made at atmospheric pressure. Extrapolation to higher pressures is not recommended. Therefore, systematic experimental investigations were carried out in a pilot plant at pressures of up to 100 bar. The experimental equipment and techniques, evaluation methods, and some characteristic experimental results are presented.
Steam reforming of natural gas with intergrated hydrogen separation for hydrogen production
Authors: Oertel Michael , Schmitz Johannes , Weirich Walter , Jendryssek‐Neumann Ditmar , Schulten Rudolf 
Published: August 2005

AbstractThe development of heat resistant permeation membranes has opened up new possibilities for the conversion of fossil energy resources. In steam reforming of natural gas, such membranes even permit a direct production of hydrogen at high temperatures during the conversion of feed hydrocarbons. Further gas processing, such as required for reformer gas in existing hydrogen production processes, is not necessary. Due to continuous hydrogen discharge directly in the reformer tube, the chemical equilibrium of the occurring reactions becomes displaced towards the products, resulting in more favourable process conditions and, consequently, in improved by 36% utilization of the feed hydrocarbons. At the same time, the hydrogen yield increases by 44%. The heat required, which is provided by a high temperature reactor, is 17% in excess of that in conventional plants. It can be expected that the simplified process design will produce substantial cost advantages over the existing processes for the production of hydrogen.
Chemical technology of natural gas – its present state and prospects
Authors: Preuß Ulrike , Baerns Manfred 
Published: August 2005

AbstractAgainst the background of long‐term availability of natural gas, its present technology and future prospects are described. Particular emphasis is put on the oxidative coupling of methane to C2+hydrocarbons: (1) Catalyst development, activity, selectivity and deactivation as well as reactor operation are discussed; (2) a tentative process scheme is put forward and its economics evaluated with respect to ethylene production.
Rear surface deposition of fine particles on spheres — eddy deposition or electrostatic effects?
Authors: Dau Güunter 
Published: August 2005

AbstractThe aim of this investigation is to show the demarcation of two possible mechanisms for surface deposition of fine particles on the rear surface of single spheres. By means of single particle trajectory computation, based on numerically determined flow fields (Remax = 103), it is shown that the mere existence of a wake is not in itself sufficient to produce eddy deposition. In addition, the particle's motion must undergo a lateral transfer promoted by fluid trubulence, in order to effect eddy deposition commencing at a Reynolds number of about 100. On the other hand, rear deposition, influenced by electrostatic forces, especially by the Coulomb force, is possible at any Reynolds number. Consequently, for Reynolds numbers of less than 100, only electrostatic effects can produce rear surface deposition. In the range of high Reynolds numbers, the coexistence of both mechanisms is possible. Very high Reynolds numbers (Re > 103) and low Stokes numbers indicated the predominance of the electrostatic effect over eddy deposition, whereas at very high Reynolds numbers and medium to high Stokes numbers the electrostatic effect is only predominant in presence of high electrostatic charges.
Theory and application of an alternative correlation flowmeter
Authors: Braun Hans , Füg Michael , Schneider Georg 
Published: August 2005

AbstractCorrelation flowmeters have been used in the scientific field for many years and are actually gaining greater commercial importance due to an increasing number of applications in industrial plants. The importance of the correlation method is based on the fact that essentially no alternatives exist for measuring velocity and mass flow rate in pneumatic conveyors. However, the hitherto employed transit time correlation method leads to results which are clouded by uncertainties. The commonly used theoretical model of the measurement process does not explain these effects satisfactorily. Therefore, the theory of non‐intrusive flow sensors is reinvestigated from a physical standpoint. The derived model permits a discussion of the transit time correlation method in some detail. Furthermore, this model leads to an alternative sensor arrangement and signal processing scheme which makes it possible to measure the true mean velocities. Examples of experimental results are given.
Calo‐visco‐densimeter: A multipurpose apparatus
Authors: Zech Helmut , Knapp Helmut 
Published: August 2005

AbstractA multipurpose apparatus was designed, built and operated with the aim of a simultaneous determination of enthalpy of mixing, heat capacity, kinematic viscosity and density of liquid mixtures at 240 < T < 370 K and 1 < p < 25 bar. Its operation was monitored by a PC. Details of design and the first experimental results are presented.
Effect of some operating variables on the flotation of aluminium particles
Authors: Abdo Mohamed S. E. , Darwish Amina M. 
Published: August 2005

AbstractThe effects of impeller speed, air flow rate, cell concentration, agitator size and cell volume on the recovery of aluminium particles have been studied in a KHD Humboldt Wedge AG machine, using alkyl benzene sodium sulphonate paste as collector and pine oil as frother. The recovery yield increased with increasing impeller speed, air flow rate, cell concentration and cell volume, up to a certain range, whereafter it decreased. A decrease in the recovery yield was observed on increasing the agitator size. A mathematical model has been developed to correlate percentage recovery with the above variables.
An automatic laboratory reactor for homogeneous polymerization of methyl methacrylate
Authors: Budde Uwe , Reichert Karl‐Heinz 
Published: August 2005

AbstractAn automatic stirred tank reactor of laboratory scale has been developed for on‐line measurement of conversion, viscosity, and molar mass distribution of homogeneous polymerizations. For these on‐line measurements, a fraction of the reaction mixture is bypassed through a densimeter and a viscometer. Samples are taken at intervals of 15 min, diluted semi‐automatically, and then injected into a high performance gel permeation chromatograph for determination of the molar mass distribution of the polymers. A microcomputer collects the measured data, calculates the monomer conversion and the output data for different control units. In this study, methyl methacrylate is polymerized batch‐ and semi‐batchwise with ethyl acetate as solvent and in the presence of different initiators. The semi‐batch polymerizations are carried out at constant reaction rate by feeding the initiator and at a given increase in viscosity by feeding the solvent.
Two‐phase flow and mass transfer in scrubbers
Authors: Schmidt Burkhard , Stichlmair Johann 
Published: August 2005

AbstractExperimental investigations were carried out in spray scrubbers of different sizes with cocurrent flow of gas and liquid. Of special interest were the local processes in the mass transfer zone. The scrubber was operated with warm water/air system (cooling tower) to obtain detailed information about mass transfer. Air is being humidified with water vapour, which in turn leads to a temperature drop in the liquid. The liquid temperatures are relatively easy to measure and are shown as liquid isotherms. In the case of plug flow, the liquid isotherms should be straight horizontal lines. In reality, significant deviations from plug flow are caused by the transfer of liquid to the walls. A large part of the liquid forms a film flow at the wall. Furthermore, nearly all the mass transfer is completed in the zone of liquid atomization immediately beneath the nozzle. The number of measured transfer units was between 0.5 and 2.0 and was significantly influenced by the liquid flow rate. Based on the improved knowledge of the proceses inside the scrubber, a simplified model has been developed. Since the model simulates all the essential processes inside the mass transfer zone, liquid distribution and mass transfer efficiency can be approximately predicted.
Thermally safe operation of a semibatch reactor for liquid‐liquid reactions–fast reactions
Authors: Steensma Metske , Westerterp K. Roel 
Published: August 2005

AbstractAccumulation of the reactant supplied to a cooled semibatch reactor (SBR) will occur if the mass transfer rate across the interface is insufficient to keep pace with the supply rate. Then, due to a low starting temperature or supercooling, the reaction temperature does not rise fast enough to the desired value. This accumulation may eventually lead to a temperature runaway. We investigated the possibility of such an event for reactions of the type “chemically enhanced mass transfer” or “fast” and found that only low distribution coefficients, i.e. 10−4 or lower, can lead to accumulation. At higher distribution coefficients, the mass transfer rate across the interface of a well‐mixed dispersion is generally sufficient to prevent accumulation. A thermal runaway in the fast regime exerts a moderate effect, because the effective activation energy is halved. Calculations for the “instantaneous” reaction regime, regarded as a special case of fast reactions, show that there is no runaway possible.
Mass transfer during the removal of dissolved heavy metals from wastewater flows in fluidized beds of ion exchange resins
Authors: Zarraa Mahmoud A. 
Published: August 2005

AbstractA fluidized bed of cation exchange resin was used for the removal of cupric ions from a simulated wastewater effluent consisting of copper sulphate solution. Variables investigated were: superficial liquid velocity, particle diameter, bed height and copper sulphate concentration. These variables were studied with respect to their effect on the solid‐liquid mass transfer coefficient. The coefficient was found to increase with increasing superficial liquid velocity. Increasing particle diameter, bed height and copper sulphate concentration were found to reduce the mass transfer coefficient. The experimental data can be correlated by the equation

equation image

valid for the following conditions: 0.23 < Re1 < 2.27; 0.52 < ϵ < 0.87; 0.0127 < dp/d < 0.0417 and 0.0095 < dp/L < 0.125.
Experimental studies on parametric sensitivity of a batch reactor
Authors: Haldar Raghunath , Rao Damaraju Phaneswara 
Published: August 2005

AbstractRunaway behaviour of exothermic reactions in a batch reactor has been studied experimentally on the example of acetic anhydride hydrolysis catalyzed by sulphuric acid, in a 700 ml batch reactor. High parametric senstivities of peak reactor temperature with respect to initial reactor temperature and catalyst concentration were obtained.
Experimental studies on semibatch reactor parametric sensitivity
Authors: Haldar Raghunath , Rao Damaraju Phaneswara 
Published: August 2005

AbstractRunaway behaviour of an exothermic reaction in a semibatch reactor was studied experimentally on the example of hydrolysis of acetic anhydride catalyzed by sulphuric acid, in a 700 cm3 thinwalled stainless steel stirred reactor, 10.2 cm in diameter and 13.0 cm high. The reactor was partially immersed, to a depth of 2.1 cm, in a thermostatic bath, in order to obtain sufficiently rapid cooling of its contents. A reaction run was performed by first introducing water, acetic acid and sulphuric acid into the reactor. After the contents attained bath temperature, acetic anhydride at room temperature was fed to the reactor for a fixed time period, at a constant flow rate. When water was present in excess of the stoichiometric requirement and addition of acetic anhydride completed before the reactor attained peak temperature, the system showed sensitivity to coolant temperature and sulphuric acid concentration. When the reactants were present in stoichiometric quantities and addition of acetic anhydride was completed after the reactor attained peak temperature, the system did not exhibit any significant parametric sensitivity.
Experimental and analytical study of countercurrent flow limitation in vertical gas/liquid flows
Authors: Stephan Martin , Mayinger Franz 
Published: August 2005

AbstractAn experimental and analytical study of adiabatic countercurrent flow limitation (flooding) in single vertical ducts is reported. The experiments were carried out in a rectangular channel using saturated liquid and vapour of Refrigerant 12 (CCl2F2). The steady‐state liquid delivery (flooding) curves as well as local pressure drop and void fraction distributions in the countercurrent flow were measured in a range of system pressures from p/pcrit = 0.16 to p/pcrit = 0.31, and for various total liquid injection rates and locations. The measured flooding curves j1 = f(jg) as well as pressure drop and void fraction during partial liquid delivery (j1 < j1in) were not affected either by the axial liquid feed location or by the excess liquid rate carried upwards by the vapour. Moreover, for given flow conditions during flooding pressure drop and void fraction were essentially the same at different axial positions. Radial void fraction distributions evaluated from optical fibre probe data indicate an annular‐type flow pattern. Based on this experimental evidence, a mechanistic core/film flow model was developed for the calculation of flooding. The analytical results are compared with the present high pressure and with comparable atmospheric pressure experimental data, showing reasonable overall predictions not only of the flooding curves, but also of the pressure drop in countercurrent flow.
Mass transfer improvements in single phase in regular packings
Authors: Colazo Jorge A. , Böhm Ursula 
Published: August 2005

AbstractTwo ways of enhancing liquid to solid mass transfer in regular packings are proposed and investigated: the introduction of a fluidized bed of inert particles and of turbulence promoters by constructing the packing from expanded metal. It is shown that both systems can be of considerable benefit in improving the mass transfer performance: up to 200% in the first case and up to 130% in the second case. However, the energy dissipated by fluidized particles is excessive in comparison to that consumed by turbulence promoters.
Physical properties of the NO‐absorbing system cupric chloride‐tributyl phosphate
Authors: Yavuz Ömer Nafi , Gestrich Wolfgang 
Published: August 2005

AbstractFor pure tri‐n‐butyl phosphate (TBP) as well as solutions of cupric chloride in TBP and for mixtures of TBP with n‐decane or solutions of cupric chloride therein, the density, viscosity, physical solubility of nitric oxide (NO) and its diffusion coefficient have been determined and a discussion is presented