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Capillary forces are very important considering the handling of powders as they, in general, exceed other adhesion forces. These capillary forces are dependent on several different parameters. Especially the distance between the particles is an important parameter. For example, in moving bulk solids a large variety of distances between particles will occur. Therefore, the distance-dependence of capillary bridges was investigated with a numerical simulation method, assuming thermodynamic equilibrium which is attained very fast for small particles. This method uses the Kelvin equation and the Young-Laplace equation to calculate numerically the shape of the capillary bridge without any assumption regarding the shape. The force is eventually derived from the meniscus shape. The distance becomes extremely important when the capillary liquid bridge between two surfaces is only determined by capillary condensation depending on relative humidity. Only a slight increase of the distance within the fraction of a nanometer changes the behaviour of the capillary force significantly. Furthermore, the influence of the force on the separation of particles will be presented. The force decreases almost linearly with increasing distance for a wide range of distances and consequently, a contact stiffness for capillary bridges could be derived. These results may e.g. be used in DEM models. Also, the maximum separation distance of capillary bridges in thermodynamic equilibrium and the correlation with the according bridge volume was investigated. As two limiting cases for capillary bridges at varying distances one can assume either a constant curvature, i.e. infinitely fast attainment of equilibrium, or a constant volume, i.e. infinitely slow attainment of equilibrium. Therefore, a comparison of these two possibilities will be presented and discussed as well.

Suspensions are subject to confinement induced structuring, i.e. layering, at the confining surfaces. While most of the previous work focused on layering in Couette cells, the present study aimed to characterize the resulting layers at the plates of a parallel plate rheometer with regard to their relative particle concentration. The particle concentration profile over the radial distance was characterized for various mean concentrations and gap heights. To this end, we mapped the distribution of fluorescently dyed tracer particles in density and refractive index matched suspensions. The results indicate that layering at the surfaces stabilizes as the ratio between gap height and particle diameter increases. For lower gap heights, i.e. as the suspension approaches a two dimensional state, the layer concentration was non-uniform over the plates. In general, results were quantitatively different for the upper and lower plate and the concentration profiles were noticeably asymmetric. We conclude that this is probably the result of the rheometer loading or the start-up process. The stable layers as well as the inhomogeneous particle distribution in general offer an explanation for the lack of transferability of viscosimetric results between different setups.

The precipitation of sticky and ultrafine particles has become increasingly important. Biomass burners are one important example for ultrafine dust emission sources with ever growing importance. Therefore, a baghouse filter has been developed, which combines excellent separation efficiency (> 99%, clean air dust loading of Therefore, extended tests on recycling of used precoat material have been performed. Particularly, the influence of precoat injection parameters and various mixing strategies of used and virgin powder for refreshing the precoat material have been investigated. Different mixtures have been characterised by their ability to disintegrate, flowability and filtration behaviour. It is clearly demonstrated that upon redispersing the used precoat fine dust mainly adheres to the coarse precoat with only a limited number of dust agglomerates being produced in addition. For each kind of precoat a minimum amount is determined in order to ensure a long-term stable process. This way a saving potential of between 40–67% has been found. An economic and ecologic process has been developed to precipitate ultrafine dust in a baghouse filter system using precoat materials.

Because of the large surface area of colloids interface effects are dominant in contrast to volume effects. The study presents experimental results of the direct transfer of magnetite nanoparticles from an aqueous to a non-miscible organic phase. The starting point is a water-based colloid that is synthesized through a precipitation reaction. The transfer is based on the adsorption of surfactants onto the particle surface at the liquid–liquid interface. While penetrating the liquid–liquid interface, the particles are covered with surfactants and a partial de-agglomeration is initiated. The intention is to produce a stable organic colloid, which has important applications in industry. The optimized process parameters for the successful phase transfer process, the adsorption reactions at the liquid–liquid interface and the stabilization of primary particles in the organic phase are demonstrated.

A two-phase biotransformation process for selective hydroxylation of n-octane to 1-octanol via Pseudomonas putida KT2440 harboring heterologously expressed P450 monooxygenase from Mycobacterium marinum is presented. Maximum cell-specific conversion rates of 12.7 mgoctanol gCDWh–1 were observed not only in shaking flasks but also in 3.7-L-bioreactor studies. The bioreactor experiments were performed avoiding explosive gas mixtures by lowering volumetric power input, aeration rates and substrate concentrations. Based on a stoichiometric network of P. putida KT2440 topological studies were carried out. As a conclusion, potential limitations of NAD(P)H and/or ATP supply at production conditions can be excluded. Hence, the great potential of the host for further increasing conversion is outlined.

Wood-Plastic-Composite (WPC) zeigen im Vergleich zu reinen Kunststoffen ein sehr unterschiedliches und uberaus komplexes Material- und Fliesverhalten. Letzteres ist fur die Verarbeitung der Composite von entscheidender Bedeutung. Im Folgenden werden die Ergebnisse rheologischer Charakterisierungen sowie einiger Untersuchungen zum Fullverhalten im Spritzgiesprozess dargestellt. Dabei werden auch auftretende Herausforderungen und mogliche Losungsansatze diskutiert. Wood-plastic composites (WPC) show a complex and completely different material and flow behavior in comparison to pure polymers. Especially the flow behavior is very important for the processing of these composites. In the following article results of rheological characterization and investigations of the filling behavior during the injection molding process are presented. Furthermore, appearing challenges and possible methods of resolution are discussed.

In this paper, we consider a model for precipitation experiments based on the population balance equation. The study revealed a high sensitivity of the system with respect to the modeling of intrinsic parameters, motivating a comprehensive validation of the estimates. In the forward simulation the impact of the influencing parameters including surface energy, nucleus size and distribution is investigated. Subsequently we construct a simplified model of the precipitation process in such a way that it is orbitally flat in terms of control theory, which enables the inverse calculation of the parameters. The numerical results of the inverse simulation for the interfacial energy have been compared to a physical model. The possibility of solving the inverse problem provides a promising way of estimating hardly measurable quantities for more complex molecules.

Modeling of particle deposition on adjacent walls is a key issue in various applications like separation or transport processes. The present paper focuses on the modeling of turbophoretic deposition of particles in the micron size range. The first step is to evaluate the important range where turbophoresis plays an important role in comparison to other mechanisms e.g. gravity or electrostatic separation. The disadvantages of commonly used models will be analyzed and overcome by implementing a more sophisticated approach considering damping of turbulent fluctuations in the wall-boundary layer. In contrast to previous work, commonly used turbulence models are applied to solve the mean flow field of the examples under consideration. The results will show a good prediction of particle deposition in comparison to experimental values [B.Y.H. Liu, J.K. Agarwal, Experimental observation of aerosol deposition in turbulent flow, Aerosol. Sci. 5 (1974) 145–155.] by using the advanced model.

In the present work, an Euler–Lagrange approach has been applied to characterize the behavior of a heterogeneous cell population in a stirred-tank bioreactor with non-ideal mixing. It allows one to describe population behavior as the outcome of the interaction between the intracellular state of its individual cell and the turbulent flow field in the reactor. The modeling approach and the numerical method employed are based on an Euler–Lagrange formulation of the system combined with a fractional-step method to allow for a stable, accurate, and numerically efficient solution of the underlying equations. This strategy permits one to account for the heterogeneity present in real reactors in both the abiotic and biotic phases. The example of sugar uptake (phosphotransferase system, PTS) of E. coli cells growing in a fed-batch culture is used to illustrate the application of the approach. The activity of the uptake system depends on the local concentration of glucose as well as the ratio of the intracellular concentrations of phosphoenolpyruvate and pyruvate, which in turn is a function of the history of the individual cell. The simulation results point to distinct differences in the viability of the cells at different scale of operation.

Die Modellierung der wandnahen Bereiche bei der Simulation von Zweiphasenstromungen spielt in der Praxis eine entscheidende Rolle, wenn erwunschter oder unerwunschter Transport der dispersen Phase zu einer Oberflache bedeutend ist. Zweiphasenstromungen mit einer dispersen Phase werden heutzutage haufig mit dem Euler-Lagrange-Verfahren in modernen CFD-Codes simuliert. Im Folgenden wird darauf eingegangen werden, wie solche Berechnungen in kommerziellen CFD-Codes durchgefuhrt werden.

Nanoparticle precipitation is an interesting process to generate particles with tailored properties. In this study we investigate the impact of various process steps such as solid formation, mixing and agglomeration on the resulting particle size distribution (PSD) as representative property using barium sulfate as exemplary material. Besides the experimental investigation, process simulations were carried out by solving the full 1D population balance equation coupled to a model describing the micromixing kinetics based on a finite-element Galerkin h-p-method. This combination of population balance and micromixing model was applied successfully to predict the influence of mixing on mean sizes (good quantitative agreement between experimental data and simulation results are obtained) and gain insights into nanoparticle precipitation: The interfacial energy was identified to be a critical parameter in predicting the particle size, poor mixing results in larger particles and the impact of agglomeration was found to increase with supersaturation due to larger particle numbers. Shear-induced agglomeration was found to be controllable through the residence time in turbulent regions and the intensity of turbulence, necessary for intense mixing but undesired due to agglomeration. By this approach, however, the distribution width is underestimated which is attributed to the large spectrum of mixing histories of fluid elements on their way through the mixer. Therefore, an improved computational fluid dynamics-based approach using direct numerical simulationwith a Lagrangian particle trackingstrategy is applied in combination with the coupled population balance–micromixing approach. We found that the full DNS-approach, coupled to the population balance and micromixing model is capable of predicting not only the mean sizes but the full PSD in nanoparticle precipitation. 2005 Elsevier Ltd. All rights reserved.

Simulation results on the evolution of aggregate structure in aerosol processes with coagulation and sintering as the dominant mechanisms are presented. A model for simulation of the three-dimensional morphology of nano-structured aggregates formed by concurrent coagulation and sintering is applied. The model is based on a stochastic diffusion controlled cluster–cluster aggregation algorithm and sintering is modeled as a successive overlapping of spherical primary particles, which are allowed to grow in order to maintain mass conservation. This leads to computer simulated structured aggregates which are then subject to evaluation. Two different methods to determine the fractal dimension are presented which give comparable results. It is shown that even very small particles show the same fractal behavior. Furthermore, equilibrium structures assuming a constant ratio of the characteristic collision time to the characteristic fusion time are considered as well as the kinetics of structural changes due to a change in the ambient conditions.

This work investigates the effects of reduced accessible surface area of aggregate particles and of surface energy on relevant particle formation and growth mechanisms during titania formation from the vapour phase at industrial process conditions. Growth due to surface reaction and due to condensation is related to the fraction of the surface area that is exposed to the collision with single molecules. Surface shielding is found to hamper surface reaction and condensation once fractal aggregates start to form. It leads to significantly retarded precursor consumption and produces aggregate particles, which consist of more, but smaller primary particles. Surface energy data are varied within a range as proposed by available literature data. Moderate and high surface energy values result in a thermodynamic barrier to the formation of new particles and are shown to reduce the formation of seed particles by several orders of magnitude. This leads to the formation of aggregate particles which consist of a rather small number of primary particles and mainly grow by surface reaction. The primary contribution of condensation to growth of individual primary particles is shown to be very little. However, condensation should not be neglected as it has a strong impact on particle formation rates and hence on product characteristics such as the number of primary particles and primary particle size.

A simulation method is applied to calculate particle dynamics in electrostatic precipitators as characterised by particle flux density and concentration profiles in arbitrary channel cross-sections and flux density profiles of dust precipitated at the collecting electrodes (CEs). A simple statistical model allows the determination of confidence intervals for flux profiles. First, a ‘standard case’ considering full coupling of all physical phenomena occurring in this problem, i.e., electric field, flow field and particle dynamics is simulated. Subsequently, this standard case is compared to simulations with one quantity (e.g., electric field strength, turbulence intensity) substituted by a mean value which is homogeneously distributed in the precipitation zone. This reveals the relevance of the various physical phenomena: It turned out that the secondary flows had only a minor influence on the overall particle precipitation although they cause some ‘patterning’ of local precipitation. Turbulence inhomogeneity shows a stronger effect on particle dynamics. However, the electric field appears to be by far the most important quantity in simulating particle dynamics. Consequently, in order to achieve most reasonable simulation results for a given numerical effort most attention has to be devoted to field calculations, including correct boundary conditions.

Rasche technologische Entwicklungen haben fur Chemieingenieure bzw. Verfahrenstechniker neue Beschaftigungsmoglichkeiten eroffnet, wodurch sich zusatzliche Anforderungen an die Ausbildung ergeben. Der vorliegende Beitrag beschreibt die Losungsansatze im Fachgebiet der Partikeltechnik: Es findet eine noch starkere Betonung der Grundlagen statt, wobei Beispiele aus klassischen und neuen Anwendungen exemplarisch vertieft werden. Kernpunkt des Curriculums sind die Produkteigenschaften. Besonderes Gewicht wird auserdem auf die Betrachtung ganzer Prozesse gelegt. Die Vorlesungen sind in drei Ebenen strukturiert: Grundlagen, Grundoperationen und Prozesse/Anwendungen. Methodisch wird ein zweifacher Ansatz verfolgt: Die Lehre der grundlegenden Fakten wird erganzt durch eine aktive Teilnahme der Studenten, insbesondere bei der Erarbeitung von Beispielen und in Labor- bzw. Rechnerpraktika. Durch eine ganzheitliche Sicht der Universitatsausbildung sollen auch „soft skills“ gefordert werden. Mechanical Process Engineering as an Example for Educational Challenges Due to rapid technological developments new opportunities for chemical engineers evolved leading to additional demands in education. The present article describes how this challenge is faced in the subject particle technology: Fundamentals are emphasised even more, with exemplary treatment of classical as well as new applications. Key item of the curriculum is the product property approach. Furthermore, the view of complete processes is emphasised. The courses are structured in three levels: Fundamentals, Unit Operations and Processes/Applications. From the methodological point of view a twofold approach is used: Teaching the fundamentals is complemented by an active participation of the students in working on examples and application problems as well as lab and virtual experiments. By following an integrated view of university education also soft skills of students are promoted.

Electro-hydrodynamic (EHD) flows are investigated theoretically and numerically in this paper and results are presented for the flow field in model electrostatic precipitators (EPs). The resulting flow fields are shown in various representations and explained qualitatively. Numerical calculations with different flow models (non-turbulent and RANS) were conducted to investigate the influence of the flow model on the resulting secondary flows. Furthermore, a perturbation analysis is presented, leading to a simple differential equation of the Helmholtz type. This allows a more detailed view of the important mechanisms forming the secondary flows as well as being able to obtain a very fast estimation of the resulting flow field. The calculations reveal a strong influence of a vortex formation at the beginning of the precipitation zone on the whole flow field. Furthermore, a strong effect of the boundary conditions of the electric field and the operating parameters is shown.