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Notes: The vector and scalar variables describing electromagnetic fields with different requirements of continuity can be identified to four different degrees of differential forms. The association of differential forms with finite elements leads to a set of differential forms based elements (Whitney elements); they are naturally adapted to the discretization of different vector and scalar variables. With the help of a Tonti diagram, Maxwell equations can be classified by two dual sequences together with the constitutive laws of materials. The application of Whitney elements to the two dual sequences leads to two dual approximation schemes. As an example, two dual formulations for eddy current computation using potential variables and the hybrid finite element - boundary element method are derived, where Whitney 3-D and 2-D elements are employed. A numerical application is given at the end of the paper, where the dual features of the two formulations are reported.

Notes: The paper proposes an iterative procedure, called current iteration, for the finite element solution of two-dimensional steady-state skin effect problems in open boundaries. In the procedure a fictitious boundary is introduced enclosing all the conductors. On it, the magnetic vector potential is first guessed and then iteratively updated according to the current density computed in the conductors. Conditions are obtained implying convergence to the exact solution of the unbounded problem whatever the initial guess. The choice of the fictitious boundary and the selection of the relaxation parameter in such a way that computational efficiency is obtained are discussed. The greatest advantage of the procedure is its ease of implementation in a pre-existing finite element code for bounded problems. An axisymmetric version of the procedure is also described since implementation only involves minor changes as compared with the 2-D one. Examples are provided in order to clarify and validate the procedure and compare it with other techniques.

Notes: An FFT-based formulation for the computation of electromagnetic scattering from 3-D, perfectly conducting objects is presented. The formulation solves the EFIE iteratively via a conjugate gradient scheme and has the major advantage of a low storage requirement for scatterers in the resonance region. This factor, coupled with the low run-times resulting from use of the FFT to compute the associated matrices, makes the formulation a particularly efficient one. Numerical results encompassing current distributions and far-field radar cross-sections are presented for PEC cubes of resonant size. It is shown that the computed results yield good agreement compared with other numerical techniques and experimental data.

Notes: In the paper a novel finite-integration beam-propagation method (FIBPM) is presented. This method is especially suited for the simulation of optical waveguides containing extremely thin layers of complex permittivity. For calculating the propagating optical field an efficient algorithm based on expansion of the matrix exponential in Chebyshev polynomials is applied. The derivation of the propagation algorithm is given, also detailing the convergence criteria. A code for a massively parallel computer has been developed and applied successfully to complex waveguide structures used for high-power laser diodes

Notes: No Abstract

Notes: The equilibria and kinetics of adsorption of lysozyme and bovine serum albumin on the Fractogel-EMD tentacle-type cation exchanger and the Fractogel-TSK conventional cation exchanger have been studied experimentally by batch stirred-tank method. Adsorption equilibrium data corresponded well to the Langmuir isotherm. For both proteins, the tentacle-type exchanger exhibited a higher binding capacity than the conventional exchanger. This is attributed to the flexibility of the functional groups in the tentacle-type exchanger which enhance optimal electrostatic interactions. The dynamic data were analyzed by a simplified data model which lumped mass transfer resistances and intrinsic adsorption kinetics into a single rate constant. For both proteins, it was found that the tentacle-type exchanger showed a smaller lumped rate coefficient than the conventional exchanger. The difference in the values of the lumped rate coefficients was shown to be due to the influence of nonlinear equilibrium constants rather than due to any difference in rate of adsorption.

Notes: Comparative calculations of several methods of characterization for three multicomponent mixtures that include paraffin, naphthene, and aromatic fractions are shown. Each method requires different experimental information about the mixtures but all use the numerical Gauss-Legendre quadrature. The results show that characterization making direct use of the TPB distillation curve is the most suitable approach for characterizing complex multicomponent mixtures.

Notes: A mathematical model has been developed to simulate the operation of an absorption-driven multiple-effect evaporator. The model is based on mass and enthalpy balances and heat transfer rate equations of the various components of the system. The model has been validated by comparing model predictions to experimental results from the operation of a four effect absorption-driven falling film evaporator coupled with a two-effect regenerator which operated using solutions of sodium hydroxide as an absorptive medium. The model predictions are in satisfactory agreement with the experimental results.

Notes: Knowledge of the compression factor is essential for the transport, storage and utilization of natural gas. The normal way to determine this property is by using an equation of state (EOS) which utilizes the gas temperature, pressure, volume, and composition. In many industrial situations, the composition of the natural gas is not available, yet it is still necessary to calculate the compression factor. In this paper, we present an EOS which uses relative density, heating value, and diluent compositions to determine the compression factor. The applicable ranges of conditions are 220 to 500 K up to 70 MPa (-60-450°F up to 10,000 psia). The calculations agree with data within 0.1% average absolute deviatation up to 10 MPa with a maximum deviation of 1.9% near pure component critical points or mixture cricondentherms. The equation also extrapolates through data up to 70 MPa within 1.9% We present comparisons to data of AGA Report No. 8 and to data in the paper.

Notes: Complex configurations of distillation columns have been shown to consume less energy than simple configurations. These complex configurations mainly results from two considerations: either a feed split, where the condensing vapor from the top of the high pressure column is used to heat the reboiler of the low pressure column, or the overheads from a high pressure column in a distillation train used to reboil a column under lower pressure. Industrial experience shows that very often in these configurations there is still incentive for more energy reduction simply because of inefficient control. The energy integration increases the control loop coupling the system, so that the operating strategy for the columns is no longer apparent. Therefore, the dynamic behaviour and the operational constraints of such systems become very important. The use of rigorous dynamic model of the processes is an essential instruments to pursue the goal of good and reliable process control Such models allow the engineer to realistically simulate the process with the desired control system in place and to analyze the effects of equipment sizing, hest integration, and disturbances. Variable pairing proved is used to illustrate that effective control of energy-integrated distillation columns can be achieved by proper selection of manipulated variables and pairing them correctly with control variables. Hints will also be given, when multivariable predictive control schemes should be used.

Notes: Many rectification processes are used to separate corrosive substances with high boiling points. This reports deals with a new type of structured column pacing mode of corrosion-resistant carbon fiber material. These column internals allows for low pressure drop at high throughput rated with reasonable column efficiency. Experiments in columns of 50 and 100 mm diameter have been carried out to investigated separation efficiency, pressure drop and liquid holdup of the packing even at low operation pressures. In the respective columns twp geometrical different types of packing have been tested using binary mixtures of chlorobenzene/ethylbenzene with a packing geometry similar to the Sulzer EX packing, the 100 mm diameter column was filled with elements of rougher structure and smaller specific surface. Basing on the experimental results, model equations are presented, which allow the calculation of the investigated performance characteristics.

Notes: Affinity separations rely on the highly specific binding between a protein in solution and an immobilized ligand to achieve a high degree of protein purification. A mathematical model including convection, diffusion, and rate kinetics is formulated to analyze the design and operation of affinity membrane bioseparation. The model equations are solved by orthogonal collocation method. Danckwerts' boundary conditions are used. The results obtained from model simulation show that the breakthrough of the protein is significantly influenced by Péclet number, feed protein concentration, Ligand number, Damköhler number, membrane thickness, and flow rate. Breakthrough profiles are quantitatively discussed in terms of protein recovery efficiency, ligand utilization efficiency, thickness of unused membrane, and width of the mass transfer zone.

Notes: In this paper the simulation of hybrid processes containing membrane units will be discussed. For this purpose a user-defined module for simulation and design of membrane processes was implemented into the simulation program AspenPlus.The advantages can be summarized as follows:-any combination of membrane processes with all other units already implemented in AspenPlus is possible, including internal recycle streams-utilization of the physical property models and data bases of AspenPlus is possible- cost and sensitivity analysis can be performed.These benefits are demonstrated in detail for a membrane vapor recovery unit for the treatment of tank farm off -gas, for a two-stage reverse osmosis plant for organic/-organic separations and for a combination of distillation and pervaporation for the separation of a dimethylcarbonate/methanol mixture.

Notes: When properly measured and interpreted angle of repose (AOR) can be a useful method of characterising a powder. Unfortunately, a multitude of definitions and measuring equipment is used. A review of the inherent problems is presented in the first part of this paper.The second part of the paper describes the improvements made to a measuring device developed originally for measuring the angle of repose of soda ash, so that a wider range of powders can be tested. In the improved design, the tendency of cohesive and semi-cohesive powders to block the device's funnel has been eliminated.A total of 73 powders consisting of four different materials, and covering Groups A, A/C and C of Geldart's classification, have been tested using the new equipment. The results show that AOR increases systematically with decrease in mean particle size. Combination of AOR measured in the new device with aerated bulk density provides a quick, sensitive and effective method for characterising a wide range of powders.

Notes: During the spherical agglomeration process, a suspended solid is agglomerated by adding a binding liquid. First, mircoagglomerates or flocs are produced, which are compacted in the course of the process. Agglomerate size was evaluated by laser diffraction spectrometry, image analysis was used to determine the size and some adequately defined shape parameters calculated by Fourier analysis of the particle contour.The shape analysis confirms the visual observations; the compaction of the flocs is expressed by the corresponding change of the shape parameters. The influence of several process parameters on changes in agglomerate shape can be described quantitatively and help to gain an insight into agglomeration mechanisms. The particle size distributions determined by image analysis and laser diffraction spectrometry hardly differ for fairly spherical flocs or agglomerates. Concerning the size distribution of the irregular flocs, laser diffraction spectrometry measures larger particles than image analysis.

Notes: This paper describes the use of a capacitance tomography system for imaging gas bubbles in a fluidized bed in the vicinity of an air distributor plate. The results show how the solid concentration distribution varies as a function of time for three different flow regimes: bubbling, slugging and the transition to turbulent. Bubble shape, Length and coalesence can be observed. A method of spatial correlation to elucidate the bubble formation process is described.

Notes: This paper describes the evaluation of the transfer function for the TSI-short differential mobility analyzer (DMA) in the nanometer particle size rang. The TSI-short DMA is identical with the TSI-long DMA (Model 3071) but has shortened inner and outer electrodes and the insulator material Teflon was replaced by black Delin. The DMA transfer function was determined by operating two identical DMAs in series. The DMA was investigated at a sheath to aerosol flow rate ratio of between 10 and 1. Usually for particles above 50 nm the parameters of the assumed triangular transfer function, i.e. height and half-width, approach the ideal values, which depend only on the flow ratio. For particle size below 50 nm the height decreases from 0.9 at 50 nm to 0.18 at 5 nm. The half-width increase from the ideal value 0.1 to about 0.17. The observed changes of the transfer function are due to diffusional effects resulting in losses mainly in the inlet and outlet and also broadening of the aerosol stream inside the DMA. The determined transfer functions were also compared with transfer functions calculated using a theoretical model. The agreement proved to be satisfactory. The half-widths and the transmission efficiencies of the conventional TSI-DMA (Model 3071), TSI-short with Teflon and also black Delin insulator as a function of particle size are compared to demonstrate the improvements in performance.

Notes: Response of a phase Doppler system to irregularly shaped particles is examined and shown to deviate qualitatively as well as quantitatively from the spherical particles. Nevertheless, the measured phase distributions based on an ensemble of particles exhibit a high degree of order and simplicity. The experimental data and the stochastic modeling of the process have shown that the phase Doppler technique can be used successfully for in-situ sizing and velocimetry of irregular particles. In the case of irregular crystalline particles, mean size and standard deviation can be deduced without requiring any assumptions regarding the functional form of the size distribution. As opposed to other optical techniques, phase Doppler can be used, in principle, near the backscattering location, so that a single optical window would be employed for transmission of laser light and collection of the scattered signals. Furthermore, size measurements can be velocity-resolved, i.e. a size distribution can be associated with each bin of the velocity histogram.

Notes: A series of industrial powders, most of them organic, were characterized in terms of volumetric mean size, size distribution, density, particle shape, water rentention characteristics (under a series of controlled ambient relative humidities) and loosely packed and densely packed voidages (giving the compressibility). The behaviour of the powders in powder handling apparatus (a precision powder filler) was also determined. The minimum and maximum bulk densities of the powders were related to the properties of the individual particles by means of a semi-empirical equation. The filling capacity of the powder handling apparatus was found to be related to the maximum bulk density of the powder while the filling accuracy turned out to be related to the compressibility of the powder. Knowing these interrelations made it possible to predict the powder behaviour in the handling apparatus directly on basis of the particle properties.

Notes: Fiber optic dynamic light scattering (FODLS) was used to study the kinetics of aging processes in emulsions of n-alkanes stabilized by a surfactant. The method is particularly useful for this purpose because it permits measurements in concentrated emulsions. Complications that may occur in traditional DLS due to the extreme dilution, such as solubilization of the particles in the medium, can be easily avoided in this way. The experimental results show that the main aging process is Ostwald ripening. The results are in agreement with theoretical predictions based on the Lifshitz-Slyozov-Wagner (LSW) theory as far as it concerns the relation between the molecular solubility of the n-alkanes (in the aqueous phase) and the Ostwald ripening rate. This illustrates that the main rate-determining factor is the molecular diffusion of the alkane molecules through the continuous (aqueous) phase. The Ostwald ripening rate is affected by the concentration of surfactant but in all situations is higher than expected from LSW theory.

Notes: Designing modern devices for bulk solids storage and handling requires an increasingly complex understanding of the handled bulk solids' mechanical behaviour. Models able to describe the behaviour of bulk solids can neither be formulated nor their parameters determined from common shear tests, since these do not contain sufficient information especially about the materials' stiffness characteristics. The paper describes the response envelope as a measure of the deformation resistance and its experimental determination from biaxial tests. It is shown that for fine limestone powder the stiffness in compression is only about 1/70 of the stiffness in expansion. The shape of the response envelope depends only on the ratio between the principal stresses at the stress state considered, whereas the size of the response envelope also depends on the stress magnitude.

Notes: It is well established that particle size and shape substantially influence the bulk properties of powdered materials. Although these characteristics are closely interrelated, the tendency has been to analyse the particle size independently from particle shape. The aim of this work was the assessment of particle shape through particle sizing data. For this purpose, three different particle shape materials - glass beads (spherical), crushed glass (moderately irregular) and mica (lamellar) - were tested, employing four particle sizers. The shape factor selected was the Wadell's sphericity, which was evaluated utilizing distinct equations. The comparison of the results reveals problems arising from the use of approximations rather than more fundamental equations.

Notes: A novel technique to determine the size of particles suspended in a stirred vessel is investigated. The method uses microphotography to obtain a still image of the particles in situ. The equivalent circular diameter of the particles is obtained from the photographs using digital image analysis. The particles used for the test were certified particle size standards of a very small tolerance in diameter deviation. The size comparison was determined as a percent error between the measured particle diameter (equivalent circular diameter) and the diameter established by the particle manufacturer. To determine the limiting ranges of particle size and concentrations, spherical particles in a size range of approximately 1 to 10.0 μm (microns) in diameter were employed in the test. Concentrations varied from 0.00005% to 0.1% (mass basis). For each particle size, an aqueous solution of the particles was prepared at the desired concentration and placed in a stirred vessel. Photographs of the solutions were made at 25.5x, 40x, 60x and 80x magnification. For all sizes of particles, the entire range of concentration was examined.The results indicate a minimum size resolution of approximately 3μm, in a corresponding concentration range of 0.0001% to 0.05%. Similar limits on concentration were found for the larger diameter particles, although a true upper limit for the largest particle sizes was not established. The functional concentration range appears to shift towards higher mass concentrations with increasing particle size. For 2.92 μm diameter particles, the error in size measurement was found to be below 10% for a concentration range of 0.0005% to 0.05%. Additionally, a relationship between turbidity and the error was seen at low particle concentration levels where decreasing levels of turbidity generated increasing levels of error.

Notes: A new phase Doppler anemometry (PDA) signal processing method based on a Hilbert transform algorithm is introduced and analysed. By generating a 90° phase-shifted burst signal in the time domain, the envelope of the Doppler burst can be determined. In addition, this envelope is approximated by a Gaussian exponential function. The difference of the maxima of these Gaussian approximations for two related PDA bursts gives an estimate of the time difference between these time shifted signals. With the introduction of this estimation method, the restriction to the [0,360°] interval resulting from conventional signal analysis may be avoided in many cases. To investigate the dependence on SNR, burst position, burst frequency and sampling rate, results of computer simulations are presented. The feasibility of the method is demonstrated briefly by experimental results. Phase differences of more than 2000° arising from the measurement of monodisperse droplets by a conventional PDA setup could be determined.

Notes: This paper reports an experimental study on the stability, coagulation and diffusion of molecular clusters and ultrafine particles generated from organic vapors by corona ionizers. Upon leaving the ionizer, particles are made to flow within several types of vessels: depending on the specific geometry of the flow system, clusters either coagulate into large particles or are deposited on the walls. Particles larger than 4nm and molecular clusters penetrate through a wire-screen type diffusion battery, but particles in the size range between 2 and 4nm are collected. Among the organic compounds tested (aromatics, alcohols, ketones and others), only aromatic compounds appear to yield unstable clusters which grow into detectable particles (〉2nm) through Brownian coagulation. The other compounds either do not undergo the gas-to-particle conversion process or are too small to be detected. Furthermore, the presence of moisture seems to be of fundamental importance in the particle generation phenomenon. The addition of alcohols to the vapor mixture inhibits particle formation.

Notes: This paper reviews the principle of the phase-Doppler particle sizer by means of examples of the effects of varying the various experimental parameters. The examples are computed by means of a comprehensive numerical model of a complete phase-Doppler system including many practical aspects such as aperture size, polarization filters and detector properties. First the phase-Doppler principle is explained as a logical development of an interferometric measurement of the phase of the light scattered from a particle. Then the standard phase-Doppler analyzer (PDA) is decribed followed by some newer or less known variations of the principle intended to measure, e.g., in the backscatter direction, to size very small particles or to determine the refractive index of a particle. Finally, the trajectory problem in PDA measurements is briefly discussed.

Notes: A time domain unconditionally stable explicit method is presented which may be used to model processes governed by the diffusion equation such as transient heat flow. Unlike the explicit finite difference routine, the method models the diffusion process within the time step (MPWT). Being explicit, the method (MPWT) may easily account for non-linear physical parmeters and may be compared with the transmission line matrix (TLM) method of diffusion modelling in terms of its utility. Unlike the TLM model, however, the equivalent circuit does not contain inductive components which have no clear physical meaning. The MPWT method is based on a simple resistive and capacitive circuit model, which for short time steps reduces to the explicit finite difference formulation but is stable for large time steps. Good agreement has been found when results obtained using this algorithm are compared with other numerical methods and analytical results.

Notes: This paper develops an electrical analogue for a gearbox suitable for use in the time-domain modelling of many electromechanical systems, with tensor methods being used to define the changing conditions in the gearbox brought about by backlash. Unlike most existing models it is compatible with the time-varying and discontinuous models often used to describe the electrical items of a typical system, and it allows for the effects of these items of mechanical non-linearities and discontinuities such as friction and backlash.

Notes: Charged particle motion is incorporated within a transmission line modelling (TLM) field code to establish a new model which allows the investigation of field-particle interactions. The model is validated by using it to predict the trajectory of moving particles and the field and potential distributions inside a planar diode for which analytical solutions are available. The effect of space charge on the operation of the diode is also investigated. The model is then applied to study in detail a practical electron gun design.

Notes: For the interpretation of human neuromagnetic data it is necessary to compute the magnetic field of a source (e.g. a dipole) in a volume conductor (e.g. a homogeneous conducting sphere or a homogeneous head model). The Multiple Multipole (MMP) method, which is a semianalytical field calculation method, is applied to neuromagnetic field calculation for the first time. The unique feature of the MMP method is that multipole expansions are used for the description of the electromagnetic field. First a validation of the MMP method is done with the help of a spherical model and an analytical solution. Then the MMP method is applied to a realistically shaped one compartment head model. The results are compared to results obtained with the Boundary Element Method (BEM). The results suggest that it is possible to solve the neuromagnetic forward problem faster with the help of the MMP method than with the conventional numerical field calculation methods for realistic shaped volume conductor models. Further investigations are necessary to tackle the inverse problem of biomagnetism with the MMP method.

Notes: Catalyst surface characterizations have been carried out to investigate the role of dispersion on catalyst activity and to probe the occurrence of oscillations in coking levels with cycle number generally observed during multiple deactivation and regeneration schemes. The titrations were done, cycle by cycle, at 430°C after oxidation and at the same temperature (430°C) after reduction at 500°C. Results show the usually observed trend - that the dispersions after oxidation are higher than those after reduction. The average decline in dispersion from oxidation to reduction was calculated to be 39.25%. It was observed that the cycles with high toxic coke removal were characterised by high deactivation times. The deactivation times were still high even for cycles subsequent to those with low dispersion. At high dispersions the catalyst had short deactivation times, that is the small crystallites deactivate faster than large ones. The nature of reducebale coke and the efficiency of its removal is a much more determinant factor of catalyst activity than the level of metal disperision. Thus prolonged toxic coke reduction at the high temperature of 500°C, though resulting in an apparent lowering of dispersion, does not affect the quality of the catalyst. The dispersion before reduction could be retained on oxidation. Hence reduction at 500°C did not introduce sintering.

Notes: Reasons are given why the axial dispersion in a gas flowing through a packed bed may be influenced by the elasticity - or compressibility - of the fluid. To support this hypothesis, experiments have been done in a packed column at pressures from 0.13 to 2.0 MPa. The elasticity E of a gas is proportional to the pressure P and the compressibility to 1/P. The axial dispersion coefficients as determined were found to be a function of the pressure in the packed bed in the turbulent flow region of 3 〈 Rep 〈 150 if the Bodenstein number is plotted as a function of the particle Reynolds number. This is shown to be an artifact. The pressure influence is eliminated, if Bom, ax is plotted versus the ratio of the kinetic forces over the elastic forces ϱu2/E. Regrettably, Bom, ax seems to be independent of ϱu2/E. For the moment we only can conclude that Bom, ax in the turbulent region is a unique function of the velocity of the gas which flows through the packed bed. Although the fact that a constant Bo value is obtained when plotted against ϱu2/E, the experimental results are so intriguing we wanted to make them public already now. The experimental work proceeds.

Notes: The dynamic behavior of a Pt-Rh/CeO2-Al2O3 three-way catalyst (TWC) under pulsed flow operation conditions (intermittent mode), such as occur in a newly developed hybrid drive system, has been studied experimentally in a laboratory apparatus with simulated exhaust gas. The parallel hybrid system is based on the combination of an Otto-cycle engine with an electric motor and a flywheel providing a short-term energy storage. This configuration permits intermittent charging of the flywheel by the combustion engine which runs only during about 10% of the driving time. Each exhaust gas pulse (duration typically ca. 3 s) is proceeded by an air pulse, which results from the filling of the engine cylinders with air at start up and shut off. Experimental studies indicated that the air pulses have a negative impact on the performance of the catalytic converter, reducing the inherent benefits resulting from the intermittent operation mode of the combustion engine.Forced asymmetric λ-cycling during exhaust pulse was found to be most beneficial for improving catalyst performance. A simple reduced kinetic model derived from a Langmuir-Hinshelwood model for CO oxidation, which was extended by introducing CO and O2 equivalents to mimic the complex exhaust gas, was used to describe the dynamic behavior of the TWC. The model proved to be useful for finding the optimal λ-cycling conditions. Experiments with the real Otto-cycle engine exhaust proved that the reduced kinetic model is suitable for use in a closed loop λ-control.

Notes: When appropriate membrane was used for the assistance of chemical and biochemical equilibrium reactions, it is possible to enhance the yield and the purity of the reaction product by selectively adding educts or selectively removing products and to a lower the energy input and the reaction time compared to conventional process.In this paper a review on membrane reactors with special emphasis on membrane-assistance of esterification reactions and a continuous tube membrane reactor for the pervaporation-assistance of the esterification are presented. The heterogeneously catalyzed esterification of ethanol and acetic acid to ethyl acetate and water was investigated as a typical chemical equilibrium reaction.The selective and simultaneous water separation from the reaction mixture of the esterification with polyvinyl alcohol pervaporation membranes is considered to be an interesting process alternative to the conventional distillation process. Compared to the distillation process, for the pervaporation-assisted process a decrease of the energy input of over 75% and of the investment and operating coasts of over 50% each was calculated.

Notes: The paper briefly reviews the historical development of exergoeconomics, the existing methodologies, and their application. Particular emphasis is placed on the optimization of the design of new energy-conversion systems.

Notes: A critical comparison of the strength and weakness of two optimization strategies for thermochemical process is made, i.e. pinch analysis and exergy analysis. Although both methods have a unique root, i.e. the minimization of the exergy losses, pinch analysis has evolved to become an instrument of direct and optimal design of a heat exchanger network while exergy analysis as such does not give an indication about process optimization. In combination with an adequate simulation code of a process, however, it can help to find the optimum process structure.

Notes: The growth of a thin liquid film surrounded by gas pocket(s), undergoing absorption with a zero-order chemical reaction, has been simulated by an apt mathematical model in order to study the influence of various parameters involved. The solution has been obtained semi analytically using Goodman's integral method and solving the resulting differential equation by a fourth-order Runge-Kutta numerical integration algorithm. The computations reveal the strong dependence of film growth on reaction rate, diffusivity, and molar volume whereas the effect of gas-pocket volume and initial film thickness are moderate.

Notes: The optimal layout of a chemical plant is determined by both economic and environmental aspects. The mathematical approach to this problem is given by representing the process through a superstructure, including any foreseeable process topology. It is described by integer variables, whereas real variables arise from the unit models and the thermodynamic calculations. By including process constraints and an objective function, a Mixed Integer Nonlinear Programming (MINLP) optimization problem is postulated. In this paper MINLP algorithms are combined with a technique for the exergy analysis of chemical processes for the preliminary screening of process alternatives. The exergy analysis as a screening technique is advantageous due to a significantly smaller amount of required data and computing time, compared with true optimization, including cost estimation at an earlier stage of process synthesis and analysis. Thus, a broader solution space can be examined. The subsequent cost analysis has then only to be focused on a reduced set of parameters.

Notes: Existing design codes propose different methods for the analysis for the junction region of conical and toriconical shells (limit analysis, shake down analysis, Kellog design approach, area replacement method) submitted to internal pressure load. However, now it is possible to develop generally valid an very precise guidelines based on linear and nonlinear Finite Elements-Analyses. A clear difference is made between design with respect to fatigue strength and design according to load carrying capacity criteria. A. Major advantage of the Finite-Elements-Method(FEM) is the opportunity of its adaptation to given design criteria such as a strain limit or a plastification limit. It shown how design curves can be directly derived from the FE-analysis with respect to fatigue strength (stress concentration factors) and load carrying capacity (design factors for the calculation of a required wall thickness). The materials behavior in the plastic region is considered with an without strain hardening. Large deformation effects as geometric nonlinearities can be involved in the analysis. The method can easily be applied for the analysis of other pressure vessel components.

Notes: We developed the oxidation reaction of Cu(I) ion in aqueous hydrochloric solution by oxygen in a gas-lift capillary bubble column. The method of gas-liquid absorption with chemical reaction was used. Test data confirmed that the rate constant of the reaction is strongly affected by solution compositions, and that chloride ions induce an inhibition effect. The kinetical orders found are equal to 1 and 2 for oxygen and Cu(I) respectively. The influence of temperature on reaction rate constant showed the existence of a maximum value between 303 and 313K. The effect of gas-liquid of gas-liquid system on the liquid-side mass transfer coefficient kL was also investigated.

Notes: A random packing hydrodynamic simulator is designed specially to carry out experiments under reduced pressures with a counter-current flow air/water system. The simulator results (air/water system) compared to those obtained in a real packed distillation column (benzylchloride/ ethylbenzene system) show a good agreement between hydrodynamic parameters like pressure drop, flooding flow rate, and total liquid hold-up. Empirical relationships derived from the simulator experimental results are proposed allowing the calculation of the pressure drop in a packed distillation column, operating in the pressure range between 10 kPa and atmospheric pressure. The influence of reduced pressure on the HETP in the distillation column and interfacial area in the simulator was also investigated.

Notes: This paper presents results of temperature-programmed desorption (TDP) as a method for studying the acid and shape-selective properties of small- and intermediate-pore zeolites.A combination of an in situ infrared spectrometer and a downstream gas chromatograph for analyzing the desorption products is used to detect the desorption process. This is followed by a separate, newly installed microbalance facility.The studies shows that a part of the amines, esp. dimethylamine (DMA) and trimethylamine (TMA), adsorbed on the zeolites undergo decomposition, disproportionation and carbonization reaction during the TDP measurements at elevated temperatures. Comparison of the microbalance measurements and the gas chromatographic results give a good picture of the extent of these reaction.

Notes: A Comparative study of different Lewis acids (metal chlorides of valences, I, II, III, IV) has been made. These catalysts are used in the synthesis of a high molecular weight ester in a stirred tank reactor using octanoic acid and n-octyl alcohol as reactants. It was found that the best efficiency of the formatted ester (n-octyl octanoate) was obtained with ferric chloride. This could be explained by the high electronegativity and the existence of free d orbitals in the Lewis acid.

Notes: A mathematical model of the absorption of HCI gas in a spray dry tower has been proposed. The proposed model describes the mechanism of HCI removal talking into account atomized droplet size distribution and the change in the droplet state from “slurry droplet” to “dry particle”. It is found that the removal efficiency can be simulated by using the model with the constant mean diameter of droplet from the simulation results. Simulation results of the removal of HCI gas are in good agreement with the experimental data in a spray dry tower.

Notes: Cross-flow filtration is a filtration process for separation of a disperse phase from liquids. Suspension flows tangentially to a membrane and the filtrate is drawn off perpendicular to the direction of flow. Formation of a filter cake on the membrane is thus prevented, reduced, or its composition, modified. The principle of the separation is based on tow opposing effects: on the one hand, the particles are transported by the filtration flux to the membrane where they cause and increase in concentration; on the other hand, concentration differences are again reduced by the turbulence of the cross-flow and by Brownian motion of the particles. The two mechanisms compete with each other and depend upon particle size in different ways. An energetic comparison of the two effects yields the separation law of cross-flow filtration as a steady state solution of the Fokker-Planck equation. The separation law has an exponential form and assigns each particle size a separation probability with which it reaches the membrane. Once on the membrane the particles may form a filter cake, flow through the pores or return to the bulk flow. If the particles remain on the membrane the ranges of layer-free and cake-forming filtration can be calculated from the hydro-dynamic and geometric conditions of the cross-flow filter. Conventional cake filtration is regarded as limiting case. In continuous cross-flow filtration process a low separation probability through the filtration pressure on selection of the filter medium resistance.

Notes: The performance of a packed-bed biological reactor has been analysed under sinusoidal variations of substrate concentration and temperature for zero-order, first-order and Michaelis-Menten kinetics. The model equations were solved by the method of orthogonal collocation. The results show that the cyclic steady-state conversion is not affected by cyclic variations in the feed concentration. However, cyclic temperature variations with an amplitude of 20°C significantly decrease the mean exit concentration for zero-order and Michaelis-Menten kinetics compared to the constant-temperature case. The approach to cyclic steady-state conditions is estimated to be somewhat flower for zero-order kinetics than for the other kinetics models investigated. We conclude that temperature variations during the day or changes in the performance of upstream plant will not adversely affect the performance of a packed-bed biological reactor.

Notes: The scale-up of benzoyl peroxide initiated copolymerisation of styrene and butyl methacrylate is studied here. The reaction is carried out in reactors of 3, 10 and 100 1 volume. Increasing the reactor size increase the weight average molecular weight and broadens the molecular weight distribution. Reducing the agitator diameter broadens the molecular weight distribution.

Notes: In this paper a novel process for biotechnological abatement of hydrogen sulphide is presented which details the fundamentals of chemical and biological phenomena involved. The process is based on the combination of two steps to form a closed cycle which has special enviornmental advantages. The chemical step corresponds to the abatement reaction itself with absorption of the gas in a ferric solution. The biological step is related to the regeneration of the absorbing solution by means of specific bacterial strains. Particular interest is devoted to the biological kinetics of the regeneration stage, where several inhibition phenomena appear, and are also related to parameters such as temperature and pH. Results of experimental runs of gas absorption in a laboratory scale plant are also described.

Notes: Suspension polymerization of styrene was performed in the loop reactor. In order to allow wide change to the polymer particle size, a sub impeller was included within the main impeller. The sub impeller served to increase the fluid velocity and to uniformly disperse the polymer droplets during polymerization.It was investigated how the double agitation method by the main and the sub impellers affected the transient droplet diameter distribution and the final particle size distribution. The particle size could be changed widely by the double agitation method without the decrease in degree of the uniformity of the particle size.

Notes: Vanillin can be produced by oxidation of kraft lignin, with air, in alkaline medium. The optimal conditions for vanillin production strongly depend on pH and temperature. This paper addresses the effect of temperature and pH on vanillin degradation by oxidation. Experiments were carried out in a wide range of vanillin concentration, oxygen partial pressure, temperature and pH. Simple models are proposed to explain the observed rate of vanillin consumption under conditions of high alkalinity (pH〉12) and lower alkalinity (pH〈12). At pH〉12,the reaction rate of vanillin oxidation is first order in dissolved oxygen concentration [O2] and in vanillin concentration [C], i.e., (-rC) ∝[O2][C]; at pH〈12, the rate is zero order in oxygen concentration and second order in vanillin concentration, i.e., (-rC)∝f(pH)[C]2.

Notes: Process energy integration and continuous improvement of process technology are everlasting issues to ensure profitability of chemical productions. And both objectives become increasingly important due to long-term environmental effects of energy degradation, such as resource depletion, emissions and the release of “waste” heat. The key success factor for process improvement lies in combining up-to-date expertise from different areas in an overall approach. One such approach is the systems engineering concept. It helps to structure and to organize problem-solving process. We strongly believe that the increasing complexity of large and interlinked chemical production system and the tightening of global economic pressure force us to use more than ever systematic analysis and design methods to guarantee optimality throughout the entire product life. First we present a brief introduction to systems engineering in general. Then, in the main part of the paper, we give examples for optimizing the use of energy in chemical plants in order to illustrate advantages of the systems engineering concept. The examples range from improving the performance of individual pieces of equipment over changes in the process structure up to optimizing process clusters.

Notes: This paper represents an attempt to explicitly map the conceptual activities which constitute a process design task into a series of well-posed, complete and general numerical procedures. In spite of the fact that there is substantial number of design manuals and design procedures which process engineers can consult to choose the most proper approach to a particular problem, there is a remarkable lack of generality on the one side (procedures which apply to the design of a wastewater treatment process cannot be used even in principle to design a fluidized bed system), and an obvious receptivity on the other side (all procedures involve mass and energy balances at some point). With the advance of numerical techniques, virtually every procedure has been computerized, so that engineers can avail themselves of a multitude of computer tools in the majority of their process design activities: as a result of the lack of coordination among different producers though, the situation for what codes are concerned is very confusing: there are many codes which perform nominally the same task, giving (sometimes substantially!) different results when applied to the very same problem; each code sue its won set of property tables, its own I/O format, etc. Finally, with very few exceptions, these codes are not mutually compatible, i.e. the output from any of them cannot be used as the input to any of the other, not only because of the respective formats, but rather because the quantities taken to represent a certain physical process are not the same in different codes.This is a very unsatisfactory state of affairs, both for the final user and for the software producer. Unfortunately, this seems to be a problem for which commercial, technical and historical reasons make it very difficult to find a solution in the short term. The author is convinced that an early exposure to this problem and to a new approach to its solution can only benefit our engineering students, and has therefore endeavored, together with his coworkers, to devise a “modular approach” to the solution of process simulation problems. The material presented here has been originated by a series of lectures and seminars developed in the last three years for master and doctoral level students in Mechanical Engineering. The result of this “distillation” process maybe yet unripe, as they are definitely not complete: but the implications, also in terms of practical application, are very promising, and the approach deserves more attention in the future.The order of presentation of the material is historical/logical: it beings with the old fashioned slide-rule calculations and proceeds towards the most recent developments of AI base methods. The path is made clear from the very beginning: we are trying to extract from the various engineering activities all the essential knowledge which pertains to the engineer himself, with the final goal of transferring this body of knowledge - in some form suitable to machine communication - to a “universal-process simulator”, which can then be applied with a high degree of confidence to variety of particular process simulations.

Notes: The Pumping characteristic of an agitator in a tube is necessary of the calculation of its pumping capacity in configuration in the vessel with a draught tube. The general dimensionless equation of the pumping characteristic suitable for the higher Reynolds number region was derived by inspection analysis of basic equations. The new dynamic experimental method for determination of pumping characteristics is put forward. The application of this method is illustrated on a special three-blade axial-flow impeller.

Notes: A nonlinear unsteady state optimal control problem for a classical, constant diameter ethane thermal cracking reactor is formulated and solved. The process is represented by a pseudo steady state mathematical model, consisting of mass and heat balance, pressure drop, and coking equations. The performance index is of an economical nature, representing the global benefit of reactor operation over a constant operating time. As control variables, the space and time dependent skin tube temperature, the time dependent steam to hydrocarbon ratio, and the time dependent feed flow rate were considered. The results are in agreement with the process physicochemical and technological fundamentals.

Notes: The results of simulations of direct concentration control of a distillation column in industrial scale are presented. Both controlled variables, the two product concentrations, are determined by on-line gas chromatographs and are characterised by high dead times of about 30 min. For the resulting scanning control of the product concentrations corresponding decentralised PI controllers were developed and applied. The control of the product concentrations developed presents a conventional DV structure and was exemplarily tested for disturbances in feed flow and feed concentrations. The calculations carried out exhibit a good time behaviour of the whole system. On this occasion it can be stated that the control quality could be clearly improved if a steady-state decoupling by output transformation was employed. In this case the results achieved are totally comparable to those of internal model control (IMC), which was in use at the production plant for over two years.

Notes: This article presents gas kinetic calculation methods for the energy transport in hydrogen/ air and methane/ air mixture. The total molecular heat conductivity as well as its various shares are calculated and discussed for a temperature range of 400 to 3500 K and for a pressure of 105 Pa. The variation of the air/ fuel ratio under the conditions of chemical equilibrium is also investigated. As opposed to our previous article, an extension of the Chapman-Knskog method which goes beyond the classical 1st approximation for elastic collisions is applied for the evaluation of suitable calculation methods. This is carried out following the method for strong relaxing thermal nonequilibrium according to Brun. The equations applied in this work are simplified formulations for the proximity to equilibrium. The method for the evaluation of the parameters of the inelastic collision and some chosen results are presented. A discussion of the various shares of the molecular heat conductivity emphasizes the considerable influence of the diffusion and the thermal diffusion processes in fuel/ air mixtures compared to the Fourier heat conductivity.

Notes: The present paper deals with a novel hydrogen sulphide abatement process applying a combined chemical-biological process. The authors already dealt with this subject in the paper “Biotechnological H2S gas treatment with Thiobacillus ferrooxidans” [1], previously published in Chemical Engineering and Technology. This study, in particular, deals with over all process test runs in a laboratory scale plant with a single-stage immobilised biomass reactor.

Notes: A dynamic model incorporating biomass growth and liquid hold-up evolution is developed to describe a fixed bed bioreactor operation with cocurrent upflow of water and air flows. The model permits to predict cycle time and optimal operation conditions for high substrate removal and long cycle times. Simulation results are compared with published experimental results and show good model accuracy.

Notes: A new continuous-flow recycle microwave reactor suitable for organic synthesis has been developed to handle 0.51 quantities of reagents. The apparatus, which is designed for laboratory use, operates at atmospheric pressure in open- or closed-loop mode. It is fitted with a temperature control system. We describe this novel reactor and illustrate its efficiency with examples of organic syntheses carried out using both homogeneous and heterogeneous reactions.

Notes: A novel expert-system-based method for selection of sensors for process variables is presented. EXSENSEL (expert system based sensor selection) deals with 12 process variables and currently has 94 rules in its knowledge base. Despite its large knowledge base, users have to answer a set of only a few questions regarding a particular process variable, which is selected from a menu of 12 variables. A general description of the chosen process variable can be viewed before invoking the rules. Once a sensor has been selected, a brief write up on that particular sensor is also available on user's request. EXSENSEL is the successor to TRANSELEX, which is a single expert system for selection of transducers in the area of temperature, pressure, and flow measurement.

Notes: The interfacial tension of the binary system α-tocopherol/carbon dioxide was measured using the pendant drop method in the pressure range between 10 and 37 MPa at nine different temperatures: 313, 333, 343, 353, 363, 373, 383, 393, and 402 K. At every interfacial tension measurement, densities of both the liquid and the supercritical gas phase were also determined as the knowledge of these values is essential for calculating interfacial tension from the shape and size of drops. The interfacial tension decrease with rising pressure at a constant temperature and increases with increasing temperature at a constant pressure. The interfacial tension was found to be mainly a function of the mutual solubility of the two system components and of the density of pure carbon dioxide.

Notes: Distillation is a unit operation in which two main processes are involved: heat transfer for vaporizing and condensing and mass transfer for the separation of the mixture. A distillation unit can be described as an exergy converter: that is a unit which converts thermal exergy into chemical exergy. To obtain a complete graphical representation of mass, enthalpy and exergy balances in a fractional distillation, we propose the use of a diagram: the specific enthalpy (in KJ/ Kg of mixture) is plotted against the Carnot factor θ to show the heat and mass transfer effects simultaneously. The application of the methodology to the distillation of an ammonia-water mixture is presented. Conventional fractional distillation consumes a lot of exergy. We propose a new type of distillation in which the reboiler and the condenser normally located at the bottom and at the top of distillation column, are replaced by two heat exchangers integrated in the column itself. The exchanger integrated in the bottom of the column inputs heat to the column, and the other exchanger located in the upper part of the column removes heat. This arrangement minimizes the creation of entropy in the column and therefore maximizes the exegetic effectiveness. This new process, called:“diabatic” or “quasi-reversible” distillation should bring important improvement to conventional distillation, not only from the point of view of energy use (large reduction in the consumption of heat carriers fluids for heating and cooling), but also in terms of capital investment as the cost of fitting a heat exchanger in the destillation column will probably be less than the cost of reboiler or condenser and reflux head.

Notes: In the Chemical and Process Industry, liquid streams having a variable concentration solids are not uncommon. The hydrocyclone has been found to be a useful unit for the removal of particulate matter from these streams. The function of a hydrocyclone gets disturbed by an increase in the solid load concentration beyond a specified limit, and it may even overload the underflow opening. A variation of the solid load calls for a change in the split ratio of the hydrocyclone, which in turn requires an adjustment to the diameter of the underflow opening. A new technique has been developed which can automatically adjust to the change in the solid load without changing the underflow opening diameter. The split ration of a hydrocyclone can be changed by varying the pneumatic injection rate at the hydrocyclone's axis. Experiments were conducted using three geometrically similar hydrocyclones, and equations have been evolved to size the underflow opening.

Notes: In order to influence the habit of barite (BaSO4) single crystals obtained by precipitation, the tailor-made additives 2-aminomethanol, 3-aminoproponal, 5-aminopentanol, 4-aminobutane sulfonic acid, and several other growth inhibitors have been tested. The crystallization experiments have been carried out in a fully automated crystallizer with reproducible educt feed rates. The kinetics of the reaction has been measured by means of the conductivity. Scanning electron microscopic analysis of the obtained crystal habits led to the raesult that most of the additives tested did not influence the growth form of the crystals, but the predicted, tailor-made additives resulted in a more isometric crystal form.

Notes: Ultrasonic standing wave atomization (USWA) is a new process capable of atomizing both high surface energy liquids and highly viscous liquids. Atomization is achieved through acoustic forces acting upon a liquid jet which is guided into the central pressure node of a standing wave field. Spherical metal powders with minimum mass median diameters of less than 15 μm have been produced from metal melts with surface tensions of about 0.5 N/m. Organic liquids with viscosities between 1 and 10 Pas have been atomized, yielding mass median diameters from 20 to 330 μm. The influence of different operating parameters on the mass median diameter of metal melts and highly viscous liquids was evaluated. Parameters which were varied were ambient gas pressure, vibration amplitude of the transducers, mass flow rate, density of liquid, viscosity of the liquid, surface tension and the outlet diameter. The powders and sprays were analyzed with laser diffraction particle sizers. The physical background of the atomization process is discussed and an equation for the prediction of the mass median diameter is derived.

Notes: Coherent transmission and reflection of a plane wave through a monolayer of discrete particles are considered on the basis of simple and physically transparent formulae for the single scattering approximation (SSA) corrected by introducing a multiple scattering permittivity factor. This factor allows for multiple scattering of Waves between monolayer particles, opposite to the SSA. The multiple scattering permittivity factor is considered on the basis of the quasi-crystalline approximation (QCA) via Ť matrix formalism. The multiple scattering permittivity factor and parameters for obtaining coherent transmission and reflection coefficients (the effective extinction coefficient and the transmission and reflection coefficients due to rescattering) are calculated within the scope of QCA and plotted for comparison with SSA results. The expressions for these values are simplified for small Rayleigh particles to simple analytical formulae.

Notes: The light scattering technique is now widely used in particle sizing, and includes the turbidimetric spectrum method. Although it has been reported that the light scattering technique, especially the turbidimetric method, is sensitive to refractive index, quantitative studies are rare. In this work, the effects of refractive index on the turbidimetric spectrum method were comprehensively investigated and detailed results are presented.

Notes: Within the past 20 years, particle size analysis with laser diffraction (LD) has been subject to rapid development, extending the size range stepwise from 1-200 μm to about 0.1-3500 μm. The limits of LD are discussed in terms of light sources, the influence of the beam diameter, special Fourier optics and a new detector design.It is shown that the size range is not only restricted by the wavelength of the laser and the transmission limits of the medium. Its extension is mainly related to improvements in the measurement of the angular intensity distribution. Influences from stability and flow dominate on the coarse side of the measuring range. On the fine side, the spatial extension of aerosols and the resulting demand for extended working distances can be covered only in a parallel laser beam. Extended Fourier optics in combination with an adapatable beam expansion technique and a detector with virtual borders between semicircular elements overcome the existing limits and extend the size range to a lower limit of about 0.05 μm and an upper limit above 10 mm.The sensititivity limit of LD is approaching that of single particle counting techniques. For medical spray and inhaler applications, a 0.1% optical concentration can be converted to particle size distributions even for time-resolved analyses with sample intervals of a few milliseconds.The reproducibility of the sensor, with a standard deviation typically much less than 0.5%, is no longer the limiting factor. The reproducibility of the results is mainly dominated by the reproducibility of sampling, sample splitting, dispersion and the contamination of the optical path. The latter can be improved by the control of flow, especially for in-line and inhaler applications.

Notes: Dynamic light scattering has become a standard technique of investigating colloidal suspensions and polymer solutions. The experimental field autocorrelation function ĝ1 (t) can often be well modelled by a Laplace transform relating ĝ1 (t) to a distribution of decay times A(τ). In simple systems A(τ) can usually be directly related to a distribution of molecular weights, particle sizes, diffusion coefficients or other physically relevant quantities, With constrained regularization methods, the parameter-free estimation of A(τ) has become straightforward. In complex systems, the resulting A(τ) may contain several components the identification of which is not always obvious. The problem often originates in a superposition of diffusive and angle-independent components that have different variations of their respective decay times with the scattering vector. A method is presented based on a simultaneous fit of several autocorrelation functions measured at several different scattering angles, which, using simple and reasonable assumptions, yields a robust analysis of the spectra of decay times. The application of the method is illustrated on simulated autocorrelation functions and also on real experimental data obtained on a variety of different polymer systems.

Notes: A phenomenological model with 12 parameters for rotary drum granulation with the help of material balance equations taking into account the growth and death functions was developed. Experiments were conducted and the data were used to obtain model parameters with reference to the operating conditions and for validation of the model. It was concluded that the proposed model is adequate for the representation of dynamics and hence this model can be recommended for dynamic simulation leading to improved control of granulation circuits.

Notes: Microcontamination of product surfaces by deposited particles is an important problem in clean technologies. A most sensitive product to contamination by particles is a wafer during chip production. Therefore, methods for monitoring particle deposition on wafer surfaces have been developed in the last decade. A wafer with an unstructured and reflecting surface is inserted into the process equipment. After some time, depending on the process, this wafer is removed from the process equipment and is analysed with respect to the number of deposited particles using a wafer scanner. However, in situ particle detection in a process chamber is not possible with this technique. This would be possible if, instead of a monitor wafer, a transparent glass plate is mounted, e.g. in the housing of the process equipment. Then the illuminating and scattered light detection equipment can be mounted outside the process equipment. Since both the illuminating laser beam and the scattered light have to be transmitted through the glass plate, losses will occur, which will reduce the lower limit of detection with respect to particle size. In this article we estimate the detection possibilities theoretically and experimentally.A simple model based on Mie and vector scattering theory has been developed to describe the light-scattering behavior of a single spherical particle on a glass plate with random surface irregularities. The scattered light of individual particles of four particle sizes (1.03, 1.6, 2.92 and 4.23 μm) on the same glass surface and from the uncontaminated area of the glass plate was measured for unpolarized and normally incident light. The values of the scattered light from this model were compared with the experimental results. The comparison shows a reasonable agreement of the angular distribution of the scattered light. The developed model is used to predict the lower limit of detection for particles on a transparent surface. The theoretical estimations show that it should be possible to detect particles of a diameter down to 0.2 μm with the described measurement technique.

Notes: The ability to routinely make simultaneous measurements of the size and velocity of individual spherical particles is identified as a crucial component of advances in the science and technology of multiphase systems and processes. Since it is the dual beam interferometer identified here as the phase-Doppler particle-sizing velocimeter (PD) that has provided this capability, and since 1995 marks twenty years from a seminal paper by Durst and Zaré, a historical review is warranted and is presented. The roots and context of the development of PD are traced from the days of laser Doppler velocimetry (LDV) in the early 1970's through work culminating at several laboratories in the mid 1980's. A number of important contributions and the engineers and scientists responsible for those contributions are recognized.

Notes: A spectral estimation technique based on Prony's method has been used to analyse a five section microstrip interdigital filter with the TLM method. The time response of the filter is expressed as the sum of only five damped sinusoids, yielding an analytical expression for the time response. Furthermore, since an analytical Fourier transform exists for this expression, the frequency response is obtained without applying the fast Fourier or discrete Fourier transform. This typically reduces the time required for a TLM analysis by a factor of five. The approximation agrees very well with a full TLM time response. It is also shown that the numerical noise due to single precision computation of the absorbing boundary algorithm can be eliminated by digital filtering techniques. The effect of the via holes used for grounding the quarter-wave resonators of the filter has been included by discretizing them along with the rest of the circuit. Scattering parameters for the filter compare well with measurements published by Swanson.

Notes: Recently, a new method has been presented for the discrete simulation of multidimensional systems, which are described by linear partial differential equations with constant coefficients. It is based on methods customary in linear systems theory and digital signal processing and uses a frequency-domain representation of the continuous system to be simulated. A proper choice of functional transformations for each independent variable allows us to treat the influence of initial conditions, boundary conditions and excitation functions separately by suitable transfer functions. From these, corresponding discrete transfer functions and the structure of a discrete system for the simulation of the continuous problem are derived. The application of this method to wave propagation problems on uniform transmission lines is presented here. At first, the continuous problem is characterized by transfer functions; then the derivation of a discrete system is shown, and finally, some simulation results and a comparison with other methods are given.

Notes: The first part of the paper presents the implementation and performance of a new absorbing boundary condition (ABC) for truncating finite element meshes. This ABC can be applied conformally to the surface of the structure for scattering and antenna radiation calculations. Consequently, the computational domain is reduced dramatically, thus allowing the simulation of much larger structures, and results are presented for three-dimensional bodies. The latter part of the paper discusses optimization issues relating to the solver's CPU speed on parallel and vector processors. It is shown that a jagged diagonal storage scheme leads to a four-fold increase in the FLOP rate of the code, and a standard matrix profile reduction algorithm substantially reduces the inter-processor communication.

Notes: An improved combined fine-coarse mesh (CFCM) method for two transmission line models of diffusion is described. The method allows regular cells of different sizes to be connected and solved simultaneously. The CFCM method is applied to (a) a finite difference algorithm, (b) a conventional transmission line model and (c) a lossy transmission line model. The latter model is shown to be the most accurate. The proposed CFCM method is also compared with the graded mesh and the multigrid techniques.

Notes: The paper reviews some discrete probabilistic numerical techniques with particular emphasis on heat flow in inhomogeneous materials. The effects of different nodal configurations on the development of suitable algorithms are outlined and we suggest a new and consistent description for the discrete apparent effusivity. Our approach is then discussed in the context of TLM, and analogues are presented for flux relaxation time and effusivity.

Notes: We show that the general boundary condition D∂Φ/∂x + αΦ = 0 (D is the diffusion coefficient and α is a constant) in TLM diffusion modelling can be expressed accurately in terms of a voltage reflection coefficient ρ = (Δx - αΔt)/(Δx + αΔt), where Δx is the spatial resolution and Δt is the time step. Based on this general expression, the special cases of short-circuit (ρ = -1), open-circuit (ρ = 1) and matched-load (ρ = 0) boundaries can be described succinctly by α → ∞, α → 0 and α = Δx/Δt, respectively. This formulation allows for straightforward treatment of mixed boundary conditions found, for example, in diffusion-drift systems.

Notes: The paper gives an overview on mathematical optimization techniques specially suited to problems in electromagnetism. It is described how efficient optimization procedures consist of decision making, treatment of non-linear constraints, and an algorithm for minimizing the objective function. The optimization of a rectangular waveguide branching, a permanent magnet synchronous machine, and the iron cross-section of a superconducting magnet are given as examples. Optimization routines are used for the tracing of manufacturing errors in the production of superconducting coils. Finally the application of a genetic algorithm to a dipole coil design is discussed as an example for field synthesis.

Notes: Postprocessing encompasses graphic display and numerical computation. The critical process in this work is numerical differentiation. Methods of numerical differentiation of approximate solutions may be divided into three groups: direct numerical differentiation, smoothing methods based on superconvergence properties, and methods that exploit properties the solution is known to possess though the numerical approximation does not. The choice of method is determined by the problem, as well as the use to which derivatives are put: graphical display, local field calculation, mesh refinement or a a posteriori error estimation. The paper compares current derivative extraction methods and reviews progress in this field, with particular attention to superconvergent patch recovery and methods based on Green's second identity. A new modification of the method based on Green's second identity is presented, to include inhomogeneous and discontinuous materials.