bluuebunny/crossref_metadata_2025_split huggingface dataset:
Separation of liquid from vapour upon pressure relief
Authors: Muschelknautz Sebastian , Mayinger Franz 
Published: August 2005

AbstractWhen a chemical reactor is depressurized or pressure in a vessel, filled with saturated liquid, has to be decreased, generally both vapour and liquid flow out through the relief valve. Since chemical reactors are usually operated with toxic and explosive fluids, the discharged liquid which vaporizes on the ground around the vessel may reach dangerous concentrations, causing explosions or accidents with the poisonous gas. During a research project, some fundamentals were developed for the design of separation systems which separate liquid from vapour and store it in a receiver. The requirement for a separation efficiency of a least 80% is related to the condition that the separated liquid should flow back into the reactor still during the pressure relief phase. For safety reasons, both separation and re‐storage are to be carried out without the supply of external energy. Theoretical and experimental investigations of pressure distribution within the piping to the relief valve and in an integrated separator show that re‐storage of the separated liquid in the vessel can be achieved under certain flow conditions. Therefore, the separator must be integrated in the pipe at a certain height above the vessel, so that the hydrostatic pressure of the separated liquid, corresponding to the difference in height, is sufficient to lead it back through another pipe against the internal pressure of the vessel. First, several separators were tested with air‐water mixtures. A swirl separator and a reversing separator have been developed to such an extent that they appear suitable for the set task. Experimental results with air‐water mixtures and refrigerant R12 upon pressure relief show separation efficiencies of between 90 and 100% at low pressure drops within the whole operating range. As an alternative to separation outside the vessel, a rotary separator was also developed which is fixed to the outlet opening in the vessel. A centrifugal field is produced by the separator rotor and the heavier liquid is largely separated from the vapour so that only drops in the range < 100 μm flow together with the vapour towards the central standpipe. The outflowing vapour leaves the separator via 4 tangentially arranged nozzles, under critical conditions. The vapour flow momentum drives the separator rotor. The arrangement was developed and tested during various series of experiments, under conditions or pressure relief with refrigerant R12. So far, separation efficiencies between 60 and 95% have been achieved at stirring speeds of up to 2500 min−1.
Increase in viscosity and its influence on polymerization processes
Authors: Moritz Hans Ulrich 
Published: August 2005

AbstractIn the course of polymerization in homogeneous systems, the viscosity of the reaction mass increases by several orders of magnitude. The viscosity increase is affected by reaction conditions, concentration and properties of the formed polymer. Empirical correlations for homogeneous and heterogeneous polymerizations are given. Viscosity significantly affects the polymerization kinetics as well as heat, mass and momentum balances of the polymerization reactor. The influence of viscosity and its increase on conductive heat transfer, stirrer power input and cooling capacity, molecular diffusion and mass transfer coefficients, mixing time and residence time distribution in homogeneous and heterogeneous polymerizations in stirred tank and tubular reactors is reviewed.
Simulation of sintering of model supported metal catalysts
Authors: Wanke Sieghard E. , Lynch David T. 
Published: August 2005

AbstractDuring the past decade, the sintering of model supported metal catalysts, i.e. catalysts consisting of metal deposited on very thin and flat oxide films, has been intensively investigated by transmission electron microscopy. In the current paper, a mathematical model, based on an atomic migration mechanism, for the sintering of these catalysts is presented. The predictions of the model, based on Monte Carlo simulations, are in very good agreement with the experimental observations, i.e. phenomena such as ‘apparent’ particle migration, splitting and neck formation between particles are predicated by the model.
Combined process treatment of molasses fermentation waste water for biogas generation
Authors: Azzam Abdel Mouty , Abdel‐Shafy Hussein I. , Ibrahim Mohamend Z. 
Published: August 2005

AbstractAnaerobic fermentation of molasses distillery slops to biogas was carried out with the aid of an adapted and selected anaerobic mixed culture. Two different types of fermenters were used, namely an agitated pretreatment fermenter and a column fermenter with glass rings as carriers for micro‐organisms. The production of biogas in both fermenters amounted to between 0.6 and 0.8 dm3/g COD. The aerobic pretreatment of distillery slops by T. fermentans, yeast during a 4 to 6 h period allows a high reduction of COD in the subsequent anaerobic phase of the process. After treatment of the distillery slops by T. fermentans, it was possible to convert between 85 and 93% of the organic matter to methane. Conversion was about 93% with loading rate of 25g COD/litre day.
Determination of size and stress intensity factors for leaks in nozzle attachments
Authors: Wiedemann Gerhard , Strohmeier Klaus 
Published: August 2005

AbstractThe prediction of leak areas in pressure vessels is an important objective in the safety analysis of chemical plants. Using suitable design rules, a leak‐before‐break behaviour can be achieved. This contribution outlines a procedure for the leak‐before‐break design of nozzle attachments and the determination of the size of the corresponding opening area. In addition, K1‐factors and leak areas for a number of nozzle geometries have been calculated and plotted.
Conversion of methanol to light olefins over zeolite H‐T
Authors: Gubisch Dietmar , Bandermann Friedhelm 
Published: August 2005

AbstractThe conversion of methanol over zeolite H‐T was investigated in a fixed bed reactor. H‐T was prepared from Na‐T by ion exchange with HCl and NH4Cl solutions. The HCl solution caused appreciable dealumination. High yields of ethene were obtained with NH4Cl exchangeed zeolites Na‐T with 45% decationization, high proprne yields with low HCl or NH4Cl Exchanged catalysts. Low methanol partial pressures and short residence times favoured the formation of lower olefins. Lowest coking rates were observed at a reaction temperature of 693 K. The catalytic activity decrased slowly with the number of reaction/regeneration cycles. The distribution of procucts > C2 could be described by the most probable distribution of Schulz and Flory.
Advances in modelling and design of multitubular fixed‐bed reactors
Authors: Stankiewicz Andrzej 
Published: August 2005

AbstractThis paper presents a method mathematical modelling of cocurrent multitubular fixed‐bed reactors. The method is adapted to the most widespread type of industrial reactor design, i.e. the system fitted with disk‐and‐doughnut baffles. The proposed model makes it possible to estimate the influence of non‐uniformity of the heat carrier flow on the reactor characteristics, taking into account the coolant streams by‐passing via the tube‐to‐baffle clearances. Based on the model, the effect of the operating parameters as well as of some more important geometrical parameters of the reactor on an exemplary highly exothermic process of partial benzene oxidation to maleic anhydride is discussed.
Effects of turbulence on heat and mass transfer in stagnation flows
Authors: Kottke Volker 
Published: August 2005

AbstractThe influence of turbulence on local heat and mass transfer is systematically analyzed. Essential prerequisite is the availability of measurement methods, based on convective mass transfer, which allow the visualization of heat and mass transfer distributions. The results show that, even at low turbulence intensities, the flow and transport phenomena are decisively influenced by the specific design of turbulence grids and the orientation of the grid wires with respect to the stagnation line. Thereby, two different flow mechanisms occur which may interact. The anisotropy of grid turbulence leads to the “wire‐gap effect” depending on the actual position of the grid wires in relation to the stagnation line. The other mechanism is based on the wavy wake velocity distribution behind screens and grid which, in conjunction with the centrifugal instability of stagnation flows, may lead to longitudinal vortices. The results indicate why turbulence has not been sufficiently considered in the available (semi‐) empirical correlations. Information needed for an accurate prediction of heat and mass transfer in turbulence flows is discussed.
Model concept of floc disintegration in centrifugal fields
Authors: Kleine Ulrich , Stahl Werner 
Published: August 2005

AbstractA model of floc destruction resulting form mass forces in a centrifugal field is postulated and its validity examined. This model is to be regarded as a supplement to the existing shear‐loading disagglomeration models. In order to verify this additional floc disintegration mechanism, appropriate investigations were carried out with flocculated suspensions of silica and Hamburg dock sludge. As a result, in addition to floc disintegration by shear forces within a turbulent flow and in the centrifuge inlet, the existence of another mechanism was demonstrated. This consists in the floc destruction in a centrifugal field where particles in excess of a certain size, or specifically heavier components, are preferentially torn out of the floc. This floc disintegration by mass forces can lead to a classification effect in centrifuges which also subject the flocs to instant high centrifugal forces.
Dispersion behaviour of droplets in circular loop reactors
Authors: Tanaka Masato , Hosogai Kazuhiko , Sendai Takami 
Published: August 2005

AbstractA circular loop reactor was built for application to a heterogeneous liquid‐liquid reaction. In order to investigate the dispersion behaviour of droplets in the reactor, basic experiments were performed using a number of liquid‐liquid dispersions. Droplets discharged form the impeller region were found to grow due to coalescence in the circulation region. Mean droplet diameter decreased exponentially with elapsing time. An expression correlating the steady‐state mean droplet diameter with the operating conditions was derived. Moreover, the transition time required for the droplet diameter to reach the equilibrium value was determined and correlated with the operating conditions.
The contradiction in the theory of desorption phenomena: A new interpretation of the classical concept for its avoidance
Authors: Kasai Takeshi 
Published: August 2005

AbstractMost chemical engineers presently accept that the mass transfer rate in desorption from the solid to the gas phase or from the liquid to the gas phase is accelerated with increasing temperature in the liquid or the solid phase, or increasing partial pressure of inert gas in the gas phase, and/or decreasing total system pressure in the gas phase. Nevertheless, many reports about such mass transfer are still based on the former concept, which completely contradicts the actual phenomena mentioned above. Here, we discuss the contradiction and suggest a way of resolving it in terms of diffusion theory.
Influence of turbulence on transient premixed flame propagation inside closed vessels
Authors: Leuckel Wolfgang , Nastoll Willi , Zarzalis Nikolas 
Published: August 2005

AbstractThe explosion behaviour of CH4/air mixtures inside a closed 0.065 m3 spherical and a 1 m3 cylindrical vessel was investigated to determine the effect of turbulence on the structure and propagation rate of transient turbulent flames for different initial turbulence levels generated by 4 ventilators installed inside the equipment. Laser‐Doppler and hot wire anemometry were used to measure the turbulent motion. It was found that fairly uniform turbulence could be achieved in the central zones of the vessels and that the RMS‐values of flow velocity were proportional to the ventilator speed. The evaluation of burning velocity from the pressure/time records showed that, starting from an initial burning velocity which depends on the initial turbulence level, the flame accelerates as a result of pressure, temperature and turbulence effects. Maximum burning velocity coincides with the inflexion point of the pressure/time curve, and is followed by a rapid deceleration of the flame front. A linear relationship between burning velocity and measured RMS‐velocity is recognized in the observed range of RMS‐values.
Heat and mass transfer during condensation of steam in the presence of air at pressures of up to 21 bar
Authors: Numrich Reiner , Rennhack Rolf 
Published: August 2005

AbstractFilm theory under consideration of one‐sided diffusion is a satisfactory basis for the calculation of vapour condensation from a flowing turbulent mixture with non‐condensable gases. At atmospheric pressure and low condensate flow rates, coefficient equations for smooth tubes are used as a rule. At higher pressures and thus, at higher temperatures and gas densities, there are additional parameters. For instance, non‐ideal behaviour of the gas phase or the surface roughness affects the condensation process. These parameters were examined in a test plant under variation of pressure, steam concentration and temperature in a vapour/air mixture. At pressures of up to 21 bar, the Reynolds number of the gaseous phase reaches a maximum value of 128 000 and of 720 for the condensed phase. After description of the test facility, the experimental results are explained and discussed. It is shown that the experimental results are not in a good agreement with the common calculating methods. Taking into account the non‐ideal behaviour of the steam/air mixture and the roughness of condensate surface by using a friction factor ξr, all the results could be calculated with an accuracy of ± 20%. This was achived with a modification of the coefficient equation of Gnielinski [1] and by using the equation of Andreussi [2] for the friction factor of a cocurrent annular flow. With respect to one‐sided diffusion, the film theory is still applicable. The described method for the determination of local transfer coefficients includes the common calculating method. It represents an extension of the general validity of the film theory.
Study of mass transfer in a centrifugal film apparatus
Authors: Uchida Shigeo , Kamo Hiroshi , Itoh Eiji , Kybota Atsushi , Kawai Sumio 
Published: August 2005

AbstractMass transfer data are presented for absorption of oxygen in a centrifugal film apparatus. The apparatus was designed to exclude the formation of foam by gas dispersion in liquid. Cells and micro‐organisms are not subjected to high shear stress. Therefore, this equipment can be applied in fermentation processes. In the present work, experimental data and correlations were obtained on splitting of the liquid film and oxygen absorption into the film through a spiral ridge formed on the conical surface. The performance of the apparatus is found to be equivalent to those of other types of absorbers.
Characterization of mixing and residence time distributions in nozzle‐type reactors
Authors: Coker Akintunde Kayode , Jeffreys Geoffrey Vaughan , Mumford Clive James 
Published: August 2005

AbstractStudies of flow characteristics and residence time distribution, (RTD), have been undertaken in a range of geometrically similar, laboratory nozzle‐type reactors. High‐speed cine‐photography was employed to record the complex phenomena of liquid mixing in the reactor and also to record on film the colour of an injected tracer solution leaving in the effluent. A novel atomic absorption spectrophotometric (AAS) technique was applied to transform the results of the latter film into response curves. This technique provide detailed quantitative data on the residence time distributions (RTD) for different feed rates. A multiparameter model, comprising a network of CSTR's and plug flows, was developed to simulate the experimental response data. Good agreement was obtained between model predictions and experimental results. The experimental technique and theoretical approach are recommended for analyzing the flow patterns and mixing mechanisms in such reactors.
Particle collection in small laboratory cyclones as a basis for the design of large‐scale cyclones
Authors: Büttner Helmut , Ebert Fritz 
Published: August 2005

AbstractGrade efficiencies must be measured in order to characterize particle collection in cyclones. For real, irregularly shaped partcles, the grade efficiencies depend on the shape and orientation of the particles and the flow around them. Therefore, the collection characteristics of cyclones should be defined in relation to spherical particles. Deviations occurring on the use of real, irregularly shaped dusts can then be attributed to a material influence. A fast and accurate measuring technique to determine the collection characteristic for spherical particles is described, followed by the presentation of results of extensive investigations on small model cyclones. A similarity relationship is presented. The validity of this relationship was confirmed by investigations with similar, larger cyclones.
Heat transfer to liquids and suspensions in agitated narrow vessels
Authors: Frobese Dirk‐Hans , Bohnet Matthias 
Published: August 2005

AbstractThe knowledge of the heat transfer coefficient on the inner side of a heated vessel wall is of the utmost importance for the design of agitated vessels. In the case of large Reynolds numbers, the heat transfer is mainly determined by these numbers whereas, with small Reynolds numbers, the heat transfer is better described by considering the Grashof number. Investigations of heat transfer in agitated narrow vessels have shown that the height/diameter ratio exerts virtually no influence on the heat transfer when multi‐impeller stirrers are used. The heat transfer to stirred suspensions can be described by relationships valid for liquids if the characteristic data of the liquid are replaced by those of the suspension and when the solids volume concentration is also taken into account. This relationship allows the heat transfer coefficient to be calculated for given solids volume concentrations of up to 60%.
Design and analysis of a state observer for the temperature front of a retification column
Authors: Wozny Günter , Fieg Georg , Jeromin Lutz , Köhne Manfred , Gülich Horst 
Published: August 2005

AbstractIn order to achieve optimal energy‐saving, load‐dependent operation of rectification columns, development and implementation of model‐based control concepts are necessary. This paper reports on the design and step‐by‐step testing of a state observer for the estimation of two state variables which cannot be measured directly, namely the vapour rate and the location of mass transfer zone (temperature front) in the stripping section of a production column. The procedure is described, and the relevant simulation and operation results are presented and discussed. Initial experience, gained when the concept was put into practical operation, is reported.
Experienmental and theoretical combustion rates of graphite plates in hot parallel flows of air and O2/N2 mixtures
Authors: Wilhelmi Herbert , Waibel Rudi , Lippig Volker , Straub Dieter 
Published: August 2005

AbstractCombustion rate of flat graphite plates in oxidizing flows with velocities of up to 80 m/s and stagnation temperatures between 1600 and 2500 K were investigated. The flow field and its local properties were recorded in addition to surface temperature of the solid sample and change in surface structure. The experiments, in which the surface temperature of graphite was adjusted and carefully controlled by radiation shields, indicated that, under these experimental conditions, between 15 and 20 wt‐% of carbon was lost as particles of up to 100 μm which burnt rapidly in the boundary layer region. Subtraction of erosion rates from the recorded global combustion rates yield the heterogeneous chemical reaction rates, which are approximated by an Arrhenius type function for the mathematical modelling. Since steep temperature and concentration gradients occur in the boundary layer, the local values of the multicomponent transport coefficients were evaluated in order to design a more realistic computational procedure which, in addition, also includes radiative heat transfer. Computational checks revealed that, in the past, the assumption of mean constant values for the transport coefficients has led to errors of up to 100% in the evaluation of the chemical reaction and global combustion rates.
Simulation of primary and secondary reformers for improved energy performance of an ammonia plant
Authors: Ravi K. , Dhingra Subhash Chander , Guha Barun Kumar , Joshi Yogesh Kumar 
Published: August 2005

AbstractThe energy consumption of ammonia plants based on steam reforming of naphtha or natural gas can be reduced by shifting the reforming load from the primary to the secondary reformer. It is shown that lowering of the primary reformer operating temperature 20 °C results in 2% increase of unconverted methane content in the outlet stream. The increased methane content can be processed in the secondary reformer if the process air inlet temperature is increased to 400 °C. The lower operating temperature reduces the energy consumption of the primary reformer by about 6% (and the overall consumption by about 2%) and also prolongs the service life of reformer tubes.
Overproduction of lipase with staphylococcus carnosus (pLipPS1) under modified gravity in a centrifugal field bioreactor
Authors: Voit Harald , Mersmann Alfons B. , Götz Friedrich 
Published: August 2005

AbstractFermentation under modified gravity could be of interest in application to (a) increasing productivity of growth and growth linked production with microorganisms at high cell densities and (b) increasing the productivity of highly viscous pseudoplastic polysaccharide fermentation. In both cases, higher oxygen transfer rates in centrifugal fields result in higher productivities since these fermentations are usually oxygen limited. A further aspect of fermentation under increased gravity is the reduction of foam since foam coalescence time decreases with acceleration number. On the other hand, under microgravity, shear reduction would allow growth and production even for very shear sensitive organisms. In order to carry out fermentations under modified gravity, a special type of fermenter–the centrifugal field bioreactor CFBR–has been developed at the Institute of Chemical Engineering (Head: Prof. Mersmann) of the Technical University of Munich. For the first time, exoprotein biosynthesis of lipase with S. carnosus has been carried out under sterile and controlled conditions in this novel bioreactor, in presence of increased mass forces.
Flow phenomena and local heat and mass transfer in corrugated passages
Authors: Gaiser Gerd , Kottke Volker 
Published: August 2005

AbstractFlow phenomena, local heat and mass transfer and pressure drop of corrugated passages in process equipment are examined. Based on a method for measuring local heat and mass transfer, developed in previous investigations, a procedure has been formulated for the determination of local heat and mass transfer in corrugated passages. Using the analogy between heat and mass transfer, this technique allows the determination of heat transfer distributions in any structures with high local resolution. The corresponding pressure drop is presented together with the local and integral heat and mass transfer of different structures. It is shown that differences in heat and mass transfer as well as in pressure drop are due to different flow phenomena which also characterize mixing behaviour.