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Combining Power‐to‐X (PtX) processes with high temperature heat pumps (HTHP) can significantly increase their energy efficiency. Evaluating the example of oxymethylene ethers (OME) production from H2 via H2O electrolysis and captured CO2 from air shows that by upgrading waste heat streams using HTHP, a process overall energy efficiency of higher than 61 % can be achieved compared to 30 % in conventional integrated processes. Thereby, the waste heat stream from H2O electrolysis already covers the low temperature heat demand for CO2 capture via direct air capture, not only for OME but also for various PtX products. Importantly, a significant lever for the energy efficiency enhancement is the consideration of other low temperature heat‐demanding sectors. High overall process energy efficiencies and the electrification of the industry are key aspects towards a sustainable mobility sector. [ABSTRACT FROM AUTHOR]

• Systematic investigation of dispersing conditions on Pickering emulsion properties. • Correlation of Sauter mean diameters with energy density and tip speed. • Pickering emulsion filtration at high dispersed phase fractions possible. • Strong membrane-particle-solvent interactions revealed. Pickering emulsions (PE) are becoming of increasing interest for catalytic multiphase processes. Ultrafiltration of PE is a promising procedure for catalyst recovery to enable continuous processes. Dispersing conditions during production of PE are expected to significantly influence PE characteristics, and control of these properties is essential for robust process design. However, while the impact of PE composition has been studied before, knowledge on dispersing conditions is surprisingly scarce. The influence of dispersing time, speed and emulsion volume during the preparation of PE with an UltraTurrax (2 dispersing tools) on the drop size distribution, rheology, stability and filtration was investigated. In this first systematic study of PE preparation conditions, obtained Sauter mean diameters were correlated with energy density (R2 = 0.80), energy dissipation rate (R2 = 0.85) and tip speed (R2 = 0.86). All emulsions were stable for at least 10 weeks. With increasing tip speed (4–13 m/s), the dynamic viscosity first decreased, passed through a plateau value and then increased again. Filtration of concentrated PE was successful but strong membrane-particle-solvent interactions were revealed. This work contributes to a better understanding of PE properties that are essential for a sound application of PE in continuous multiphase catalysis. [ABSTRACT FROM AUTHOR]

The influence of viscoelastic flow properties on fluid dynamics using radial impellers is investigated. The use of transparent model fluids allows for the optical measurement of general flow behavior with a fluorescence dying technique. By varying viscoelastic flow properties, size of agitators and rotational frequency, the impact of these parameters on fluid dynamics is analyzed. Toroidally shaped, cavern‐like flow compartments form around the agitators in all fluids in specific rotational frequency ranges, preventing an efficient mixing. By balancing elastic with centrifugal forces, a simple model is developed with which compartment sizes can be predicted with good accuracy. The results indicate a good suitability of the elasticity number as a scale‐up criterion. [ABSTRACT FROM AUTHOR]

A fully automated three-dimensional observation of single bubble breakup trajectories in a stirred tank is demonstrated to gain unbiased and statistically relevant information about the breakup process. The mother bubble size is kept constant, independently of the stirring rate. The investigated parameter in this work is the power input. Three-dimensional bubble breakup trajectories and heat maps for the initial breakup location probability for the bottom and side views are provided. The influence of the stirrer blade angle position, at the moment of bubble detachment from the capillary, on the breakup probability is analyzed. The breakup positions are linked to the current flow field, related to the stirrer blade angle, within the tank. [ABSTRACT FROM AUTHOR]

A detailed understanding of turbulent fluid particle breakup mechanisms is essential for the accurate modeling of gas/liquid and liquid/liquid dispersions. The design of a fully automated setup for the three‐dimensional serial examination of the single bubble breakup process in a stirred tank, ensuring high repetition rates necessary for the additionally automated statistical analysis, is described. The implementation of a three‐dimensional automatic bubble breakup tracking tool is illustrated. At last, exemplary bubble breakup trajectories that show the benefits and limitations of the developed system and method are discussed. [ABSTRACT FROM AUTHOR]

In 2006, Dixon et al. published the comprehensive review article entitled "Packed tubular reactor modeling and catalyst design using computational fluid dynamics." More than one decade later, many researchers have contributed to novel insights, as well as a deeper understanding of the topic. Likewise, complexity has grown and new issues have arisen, for example, by coupling microkinetics with computational fluid dynamics (CFD). In this review article, the latest advances are summarized in the field of modeling fixed-bed reactors with particle-resolved CFD, i.e. a geometric resolution of every pellet in the bed. The current challenges of the detailed modeling are described, i.e. packing generation, meshing, and solving with an emphasis on coupling microkinetics with CFD. Applications of this detailed approach are discussed, i.e. fluid dynamics and pressure drop, dispersion, heat and mass transfer, as well as heterogeneous catalytic systems. Finally, conclusions and future prospects are presented. [ABSTRACT FROM AUTHOR]

Quantitative data on fluid dynamics in stirred tanks with viscoelastic fluids are scarcely available. Therefore, a particle image velocimetry study on flow phenomena occurring when agitating viscoelastic liquids with radial and axial impellers is presented. Different flow regimes exist, which result from interactions between elastic normal stresses and inertial forces: While for all agitators an axial pumping effect is found in the elastic regime, (semi-)radial flow patterns result in inertia-dominated flows. In the transition regime, locally limited zones exist dominated by either elasticity or inertia. This leads to a flow compartmentalization, a related pseudo-stagnation flow and reduced circulation rates. Which of the flow regimes is present can be predicted by the use of the elasticity number. With it, circulation flow numbers and flow distributions are standardized: In elastic flow conditions, these are constant. Thus, a scaling of the log-normally distributed velocities to the tip speed in this regime is possible. • Viscoelastic fluid flow quantified via PIV in a stirred tank for several impellers. • Flow reversal and compartmentalization occur with all analyzed impellers and fluids. • Categorization of flow regimes possible by the use of the elasticity number. • Unification of flow numbers and distributions by the use of the elasticity number. • Self-similarity of flows in the elastically dominated regime. [ABSTRACT FROM AUTHOR]

The pH dependant interactions of dipolar proteins and mostly negatively charged polysaccharides are well described in literature for pure substances (e.g. bovine serum albumin, gelatine, sodium alginate). In this study, the interactions were transferred to anaerobic sludge supernatant from biogas plants as an example for complex biosuspension matrices. Anaerobic sludge supernatant is often due to downstream processing by e.g. membrane filtration, where high amounts of macromolecular organic substances lead to severe membrane fouling and low permeabilies. Decreasing pH-values shifted the zeta potential exhibited by the proteins, allowing electrostatic protein-polysaccharide interactions and the formation of coacervated complexes. Median particle diameters increased from < 1 µm in the original sample to 5–15 µm in the acidified sample. The sludge samples showed non-Newtonian, shear-thinning behaviour. Comparing original and acidified samples, ultrafiltration membrane flux increased by a factor of 1.4–2.6 after acidification. Flux improvement was in good accordance with fundamental transport mechanisms reported in literature. In conclusion, it was possible to improve the ultrafiltration performance significantly by transferring well-known pH-dependant biopolymer interactions to complex anaerobic sludge matrices. This can be useful in a number of applications, e.g. wastewater treatment in MBRs, and membrane driven nutrient recovery from biological suspensions like WWTP sludge, manure, or digestate from biogas plants. [ABSTRACT FROM AUTHOR]

Anaerobic sludges taken from 16 different biogas plants were analyzed with respect to their rheological characteristics. All sludges showed temperature-dependent shear-thinning behavior with viscosities from 900 - 6000 mPa s at 20 ²C. Nevertheless, the liquid fraction of the anaerobic sludges also revealed temperature-dependent, shear-thinning behavior with viscosities well above water viscosity (2 - 40 mPa s at 20 ²C). The rheological behavior of the liquid phase could be linked to organic fractions, i.e., proteins and polysaccharides. Shear-thinning and temperature-dependent behavior was modeled by the power-law equation and the Arrhenius law, respectively. [ABSTRACT FROM AUTHOR]

A model that predicts the individual and mixed fluxes of pure solvent and surfactant through PDMS organic solvent nanofiltration membranes as well as the retention of the non-ionic surfactant Marlipal 24/70 from 1-dodecene was developed based on the solution diffusion model. In contrast to available models it requires only one fitting parameter that is independent of operating conditions. The other model parameters were estimated from detailed experimental observations independent from filtration data or literature values. Dependencies of the diffusion coefficients and molar volume on temperature and pressure, as well as membrane swelling and compaction were considered. Using the model fitted to filtration data at one operating condition it was possible to predict pure solvent flux with high accuracy for four different PDMS based membranes in a temperature range of 10–45 °C at pressures of 15–35 bar. Phenomenological behaviour of mixed solvent and surfactant flux were described accurately in every case. For temperature and membrane thickness variations, the model predicted solvent and surfactant flux within experimental uncertainty. Retentions, however, were accurately described. [ABSTRACT FROM AUTHOR]

The modification of lignin-derived compounds such as technical lignins, which are highly aromatic and therefore valuable as renewable feedstocks for the biobased product industry, is still a challenging and multidisciplinary task. An enzyme membrane reactor system (EMRS) featuring a continuous stirred-tank reactor and an external ceramic crossflow ultrafiltration membrane is a promising configuration, particularly when combined with ligninolytic heme peroxidases (PODs) as biocatalysts, such as the new versatile peroxidases (VP) described herein. However, time-dependent irreversible enzyme inactivation caused by the co-substrate H 2 O 2 and the fouling of the filtration membrane are limiting factors. To facilitate rational bioprocess development and reactor design, we present an overall modeling concept for a continuous operating mode that addresses both limitations. When including H 2 O 2 -related VP inactivation dynamic model analyses showed that two H 2 O 2 molecules were required to convert one molecule of the reducing substrate (here, adlerol). In this context, an (initial) enzyme inactivation rate k i 0 caused by factors other than H 2 O 2 (e.g. the used buffer system) was introduced. Because oxygen utilization is characteristic of normal POD actions, the continuous online measurement of dissolved oxygen concentration was useful to monitor enzyme inactivation and therefore an excess of H 2 O 2 . [ABSTRACT FROM AUTHOR]

Fixed-bed reactors with small ratio of tube to pellet diameter ( D/ dp= N) are applied especially for highly exothermic or endothermic reactions. In this contribution, aspects of an algorithm-based approach are investigated, which models spatially resolved fixed-bed reactors with small N. This approach is compared with experimental data in terms of bed morphology, resulting velocities, heat transfer, and heterogeneous catalysis. Finally, the question is discussed whether CFD can be applied as a design tool for small N fixed-bed reactors. [ABSTRACT FROM AUTHOR]

Enzyme membrane reactor systems (EMRS) offer a promising configuration for an enzymatic lignin modification/valorization by newly versatile peroxidases. This work continues in the same direction as our previous investigations using a 5-kDa tubular ceramic membrane for the fractionation of protein-ligninsulfonate model mixtures. Based on these preliminary studies, anin silicoinvestigation is carried out for approximating the maximum product yield of an EMRS per operation cycle and membrane area. As a result, a permeate flux of 4 L m−2h−1was optimal for the 5-kDa membrane. In this context, a first assessment is given regarding fluid flow-related losses in versatile peroxidase activity. [ABSTRACT FROM AUTHOR]

Coalescence modelling in liquid/liquid dispersions is a challenging task and field of investigations up to now, which becomes apparent when comparing the various existent models with their different and partly even contradictive implementation of influencing factors. In this work, systematic investigations of single drop coalescence were used to compare and validate different coalescence efficiency models regarding the important influencing parameters relative collision velocity and drop size. The impact of these parameters could be analysed independently from each other for the first time and used to identify the best modelling approach. Moreover, the numerical parameter of the coalescence efficiency model could be obtained based on single drop experiments. Using this determined parameter the simulation of drop size distributions within a lab scale stirred vessel was possible. The presented method offers the possibility of independent parameter estimation for population balance equation simulations based on single drop experiments. The application of this systematic approach allows the separate validation of submodels and reliable parameter determination by small scale investigations. On this basis a sound scale-up is possible using population balance equation simulations. [ABSTRACT FROM AUTHOR]

In the travelling wave bioreactor (TWB) an orbital movement is used to set up a quasi-periodic wave motion in the partially filled, toroidal shaped vessel. Based on computational fluid dynamics (CFD) models, this study presents detailed analyses of the fluid flow in the TWB for a wide range of operational conditions. Even though the wave propagation is shown to be greatly influenced by the rotation, it was found that the regular vessel shape facilitates a predominantly tangential flow with low back mixing, irrespective of the operational conditions. Hence, the influence of different bioreactor geometries without and with baffles is examined. The study indicates that CFD models can be used as a valuable tool for bioreactor development, because it provides a deep insight into the bioreactor's hydrodynamics and can help to reduce the number of prototypes. [ABSTRACT FROM AUTHOR]

• Mixing using steady and unsteady operations is studied. • Mixing kinetics are visualized through decolorization. • Image analysis methods for obtaining mixing curves are discussed. • Combinations of two flow patterns affect the mixing. • Strategies utilizing the hysteresis effect can reduce the mixing time by more than 50%. A non-conventional mixing strategy utilizing the hysteresis effect of propeller jets in viscoelastic xanthan gum solutions was evaluated through decolorization mixing time experiments. The experiments consisted of capturing and analyzing the images of the flow patterns illustrated by a fast acid-base indicator reaction in a rectangular tank equipped with a side-entering propeller. A non-subjective image processing method using average color was compared with the literature. The steady operation using the axial flow pattern was found more effective than the one using the semi-radial flow pattern. The time-periodic operations with appropriate combinations of both flow patterns significantly enhanced mixing, whereas an inappropriate combination extended the mixing time. The unsteady mixing concept using the hysteresis effect shortened the mixing time, even when the propeller was operated at a reduced rotational speed. Hence, the mixing strategy utilizing the hysteresis effect can reduce mixing time and power consumption simultaneously. [ABSTRACT FROM AUTHOR]

The drop size distribution is an essential process variable in liquid/liquid systems and relevant in many technical applications. It can be described by population balance equations. A coalescence efficiency model was developed to be able to describe the well-known coalescence inhibition due to changing pH value or salt concentration. The model includes the attractive van der Waals and repulsive electrostatic force according to the DLVO theory into the population balance equation framework. This DLVO model can extend existing simulations in a straightforward manner due to a conceptual implementation. Moreover, zeta potential measurements were performed and the model was applied to simulate experiments in a stirred tank. Hence, the drop size distribution could be predicted well with changing pH value. The results are discussed in comparison to simulations with existing models in literature. [ABSTRACT FROM AUTHOR]

The bubble swarm behavior in a system comparable to a flat sheet membrane module was investigated. The parameters channel depth, superficial gas velocity, superimposed liquid velocity and viscosity of the continuous phase were varied. Besides water as continuous phase, a non-Newtonian liquid was used with respect to the rheology of real waste water sludge. The gas hold-up was determined for 144 parameter combinations with high speed imaging and the shear stress – important for the fouling mitigation – was determined for 72 parameter combinations with the electrodiffusion method. To the authors׳ knowledge, this is the first application of the electrodiffusion method in a bubbly flow with a non-Newtonian liquid. For the two properties gas hold-up and the shear stress describing correlations were found taking all parameters into account. In both cases, the strongest influences were found for the gas velocity and the rheology of the continuous phase. Regarding the shear stresses, the median values were up to 3.2 Pa while the maximum values were up to 9.1 Pa. Depending on the parameter combination, a significant influence of the rheology was found disagreeing with the statement of the transferability of the results gained in water to real waste water systems mentioned in some papers. [ABSTRACT FROM AUTHOR]

Until the beginning of the 20th century, stirring was mostly regarded only marginally in most production processes. One century later, many aspects of stirring technology have been largely penetrated scientifically. This paper presents influential publications that contributed significantly to the impressive gain in scientific knowledge. The focus is put on papers dealing with the determination of power input and the characterization of liquid mixing, suspension of solids and dispersion of fluids. [ABSTRACT FROM AUTHOR]

The detailed understanding of droplet coalescence is important for the accurate description of liquid/liquid dispersions. A test cell is designed which enables serial examinations of the random coalescence process with high repetition rate, good observability and accuracy of experimental parameters. Within this rectangular test cell a rising droplet collides with a pendant one, while recorded by a high speed camera. The gained experimental data allows a validation and further development of appropriate models. The investigated parameters in this work are the drop size and the superimposed mass transfer influencing the coalescence probability. These examinations were carried out in the EFCE standard test system toluene/acetone/water. The effect of varying the drop size seems to be interfered by the different rising velocities due to buoyancy. Introducing a transferring component has a significant impact on the coalescence process. A transfer direction from disperse to continuous phase results in a coalescence probability of almost 100%, whereas the reverse mass transfer direction induces a repulsion of nearly all droplets. [ABSTRACT FROM AUTHOR]

Currently, fundamentals and technical utilization of multi-component solvent systems with tunable properties are investigated within the collaborative research center 'InPROMPT'︁ (integrated chemical processes in liquid multiphase systems). The systems are applied here for the use of long-chained olefins as well as unsaturated oleo chemicals in chemical production processes. Therefore, new methods of process development, chemical reaction control and the description of material properties are developed. In addition, integrated reaction and separation steps together with hybrid separations are investigated. Based on this knowledge the optimal design of technical processes for the conversion of long-chained nonpolar and polar components can be performed. The hydroformylation of 1-dodecene is investigated as a model reaction. Key concepts and exemplary results are presented in this article. [ABSTRACT FROM AUTHOR]

This study presents the concept of the travelling wave single-use bioreactor, based on an orbitally shaken, annular-shaped vessel. A numerical model was developed for early design studies in order to reduce the number of prototypes. The flow characteristics in two different vessel shapes were investigated. It was shown that the orbital motion combined with the toroidal shape of the bioreactor create the desired wave characteristics in the contents of the vessel. [ABSTRACT FROM AUTHOR]

Detailed measurements of dynamic and steady‐state drop size distributions were performed in liquid‐liquid systems with water and different silicone oils using an in situ endoscope technique in a discontinuously operated stirred tank. The oils used as the dispersed phase vary in dynamic viscosity, while density and interfacial tension are nearly constant. The performance of a population balance model for partially mobile interfaces and its ability to predict steady‐state and dynamic Sauter mean diameters and the complete drop size distributions as a function of dispersed phase viscosity and different process parameters are evaluated. Furthermore, the impact of different daughter drop size distribution shapes on simulation results is quantified. [ABSTRACT FROM AUTHOR]

Abstract: An evaluation of several breakage rates from the literature based on single drop experiments was carried out. This data was collected in a single drop breakage cell under turbulent conditions, comparable to those in a stirred tank. For a constant initial diameter and flow velocity at least 750 single drops have been investigated to measure the breakage time and probability, using high-speed imaging. These results were used for the determination of breakage rates by the product of the inverse of breakage time and the breakage probability. The same subdivision was carried out for the literature models. These differentiations in the analysis showed that published models for the breakage probability are more or less similar and in good agreements with the experimental results. Proposed approaches for the breakage time are contrary. The experiments support the assumption of some researchers that the breakage time rise with increasing drop diameter. The magnitude of the predicted values of the breakage time for all kind of models is one or more magnitudes higher than experimental results in this study and from literature. Furthermore the influence of the physical properties, like viscosity or interfacial tension, is only poorly reflected in the available models. These analysis results lead to an improved breakage time model, which takes into account different breakage mechanisms and the influence of viscosity and interfacial tension. Combined with a breakage probability from literature, this new model leads to an excellent prediction of the breakage rate for the investigated single drops. [Copyright &y& Elsevier]

Literature reports biocatalytically active static emulsions (BASE) as promising systems for the preparation of biocatalysts designed for synthetic use in organic media. Their excellent catalytic performance is attributed to the numerous micropools of dissolved enzymes independently dispersed in silicone beads. Here, a systematic study of the structure and morphology of BASE and optimization in terms of bead size distribution and overall catalytic performance is presented. The study relies on beads obtained by using a novel preparation method that enables a considerably improved reproducibility of the particle size and catalytic activity in separate batches. A large interfacial area of 0.023 m2 g−1 material was calculated. The adjustment of bead composition increased the apparent catalytic activity of entrapped lipase A from Candida antarctica (CalA) to 0.71 U gBASE−1, which is almost twofold higher than that previously reported. The specific activity remained in the range of prototype BASE (0.21 U mgprotein−1), which nevertheless is about 53 times higher than that reported for CalA entrapped in a sol-gel. [ABSTRACT FROM AUTHOR]

• The torque and thrust of propellers in viscoelastic fluids are studied. • Hysteresis effects in torque and thrust are analyzed. • Transformation of flow patterns is identified by dynamic thrust measurements. • The power consumptions of the two occurring flow patterns are similar. • The axial thrust is appropriate for distinguishing the two flow patterns. The hysteresis effect of propeller jets in viscoelastic fluids provides a new idea for improving the mixing process related to viscoelastic fluids, such as wastewater digestion. However, the application of this idea to industrial equipment requires a feasible method for flow pattern detection. This work aimed to investigate the hysteresis effect of propeller jets in viscoelastic xanthan gum solutions in terms of the torque and the axial thrust. The axial thrust and the torque were measured using a rheometer equipped with a marine propeller. Both the averaged and the dynamic results were analyzed. The axial thrust was found to be appropriate to distinguish the semi-radial and the axial patterns in the hysteresis range. The difference in torque between the two flow patterns at the same rotational speed in the hysteresis range is insignificant. [ABSTRACT FROM AUTHOR]

The filterability of activated sludge is an important factor for the economical operation of membrane bioreactors (MBR). In the literature mainly investigations on sludge dewaterability in respect to further disposal are published. In this study, a procedure for determining filterability in a crossflow test cell is introduced. Its features are: no increase in sludge concentration during batch trials, crossflow conditions, and little impact on the sludge structure. The activated sludge filterability is given as the ratio of permeate flux after 40 min of operation to clear water flux. Sludge samples of eight different MBR and one conventional wastewater treatment plant (wwtp) have been examined and compared. Contrary to the literature, no impact of suspended solids (SS) concentration, sludge viscosity, or extractable extracellular polymer substances (EPS) concentration on the filterability was found. Instead, the composition of the liquid phase was found to effect most the filterability of activated sludge, a major influence being the concentration of suspended EPS: the higher the suspended EPS concentration, the lower the filtration index. Suspended EPS concentration increases with high mechanical stress in the MBR and high F/M ratios, if the treated wastewater contains considerable amounts of proteins or polysaccharides. [Copyright &y& Elsevier]

Fermentations, utilizing a membrane bioreactor (MBR) can be advantageous as cells are retained in the vessel while soluble products are continuously withdrawn. It can be operated at high cell density, which allows increased productivity. Since hydraulic and solids residence times are independent of each other, MBRs offer an additional degree of freedom for process control. MBRs can be biologically distinguished from batch fermentors for various reasons: Like chemostats, by being operated in a distinct growth phase production of unwanted metabolites can be reduced. In addition, high cell densities may cause changes in metabolism. Although MBR fermentations have been studied frequently this influence of the operational mode, i.e. the membrane''s presence, has rarely been the main research focus. In this study, influences of the operational mode on kinetic parameters and productivity of Ustilago maydis are investigated by comparison with batch and chemostat cultures. In MBR fermentations, biomass concentrations rise up to 40 g·L−1. Possibly due to the effect of these high cell densities a low growth rate state is reached even at non-limiting substrate concentrations. MBR productivity reaches a maximum just after the onset of continuous fermentation and later decreases. Although the general possibility of MBR fermentation is shown, this highlights the need for optimization. [Copyright &y& Elsevier]

The filterability of activated sludge is an important factor for the economical operation of membrane bioreactors (MBR). In the literature mainly investigations on sludge dewaterability in respect to further disposal are published. In this study, a procedure for determining filterability in a crossflow test cell is introduced. Its features are: no increase in sludge concentration during batch trials, crossflow conditions, and little impact on the sludge structure. The activated sludge filterability is given as the ratio of permeate flux after 40 min of operation to clear water flux. Sludge samples of eight different MBR and one conventional wastewater treatment plant (wwtp) have been examined and compared. Contrary to the literature, no impact of suspended solids (SS), concentration, sludge viscosity or extractable extracellular polymer substances (EPS) concentration on the filterability was found. Instead, the composition of the liquid phase was found to effect most the filterability of activated sludge, a major influence being the concentration of suspended EPS: the higher the suspended EPS concentration, the lower the filtration index. Suspended EPS concentration increases with high mechanical stress in the MBR and high F/M ratios, if the treated wastewater contains considerable amounts of proteins or polysaccharides. [Copyright &y& Elsevier]

Mixing in biogas fermenters is complex due to the non‐Newtonian rheology of biogenic substrates, which exhibit both pseudoplasticity and elasticity. It is yet unclear how these non‐Newtonian properties affect propeller flows and the mixing behavior in fermenters. Therefore, propeller flows in Newtonian as well as shear‐thinning inelastic and elastic fluids are compared numerically and validated against particle image velocity (PIV) data. Elastic normal stresses lead to an increase of pumping rates in the laminar regime and a suppression of the formation of a propeller jet in the transitional regime. Thus, flow rates are severely overestimated by the inelastic, shear‐thinning model in this regime. The results indicate that elasticity is critical for an accurate modeling of flows of biogenic substrates. [ABSTRACT FROM AUTHOR]

• Flow fields of Newtonian and non-Newtonian fluids were studied. • Hysteresis effect in viscoelastic fluids was investigated. • The transformation processes between two flow patterns were visualized. • The semi-radial and axial flow pattern were described as laminar and turbulent flow, respectively. • Reynolds number was incapable to characterize the flow condition in the hysteresis range. This work aimed to investigate the flow pattern transformation process resolved in time and to propose a physical explanation for the hysteresis effect of a propeller jet in a viscoelastic fluid. The propeller jet flow in xanthan gum solution was measured using PIV (Particle Image Velocimetry) and UVP (Ultrasound Velocity Profiler). Based on the distribution of turbulence intensity, the semi-radial and the axial flow patterns generated at the same rotational speed were classified as laminar and turbulent flow, respectively. Therefore, the Reynolds number was considered inappropriate to characterize the flow fields in the hysteresis range, since both laminar and turbulent flow may occur at the same Reynolds number. The distribution of normal stresses derived from the flow induced structure was considered as the determining factor for the flow field formation. [ABSTRACT FROM AUTHOR]

An accurate prediction of turbulent heat transfer in packed-bed reactors is fundamental for the design and performance of such reactors. Various classes of Reynolds-Averaged Navier-Stokes models are available in the literature for predicting turbulent heat transfer via closing the Reynolds stress and Turbulent Heat Flux terms. In this work, we investigate the accuracy of representative unsteady RANS turbulence models in modeling heat transfer characteristics in packed-bed reactors. For this accuracy assessment, the performance of the examined unsteady RANS models is compared with particle-resolved Direct Numerical Simulations including heat transfer. The simulations are conducted in a three dimensional periodic domain consisting of randomly arranged cylindrical particles for Reynolds number R e p = 1000. The extracted mean quantities (e.g. velocity and temperature), turbulent heat flux components and turbulent kinetic energy are used as a reference for the RANS models' accuracy assessment. The SST k − ω and Spalart-Allmaras models performed well in predicting mean fields. However, all models tended to mispredicted the turbulent quantities including the turbulent viscosity and heat flux vector. The thermal field calculations rely on the turbulent viscosity based Simple Gradient Diffusion Hypothesis for modeling turbulent heat flux, which introduce challenges in capturing the coupling between thermal and turbulent fields. • pr-DNS of flow in a packed unit composed of cylindrical particles was performed. • The efficacy of URANS models for modeling turbulent heat transfer was evaluated. • It was found that all models struggled in predicting the turbulent heat flux and viscosity. • The SST k − ω and SA models demonstrated efficacy in forecasting the mean fields. [ABSTRACT FROM AUTHOR]

Abstract: A long-term study was carried out to evaluate the performance of submerged membrane sequencing batch reactors (SM-SBR) for greywater treatment. Three pilot plants were operated in three different countries with distinct wastewaters to prove that treated greywater can be used for reuse purposes. In all plants the permeate quality fulfilled in most cases the high mandatory values of different European directives. Membrane permeability declined significantly within a period of three to four months so that recovery cleanings were necessary 3 to 4 times a year. In general, the treated greywater from an SM-SBR can be reused for irrigation or cleaning purposes. SM-SBR for greywater treatment are especially interesting in cases of space limitations where the small footprint of the system can outweigh inconveniences like frequent chemical cleanings. [Copyright &y& Elsevier]

• Flow fields of non-Newtonian fluids were studied. • Hysteresis effect in steady state flow patterns was investigated. • Rotational speeds and flow histories affected the flow patterns. • Rheological properties affected the hysteresis range. • Particle Image Velocimetry and Ultrasound Velocity Profiler were compared. Contrary to existing knowledge, the flow field showed a hysteresis effect when the rotational speed varied. The speed up operation in hysteresis range generates a semi-radial flow field, whereas the slow down operation causes an axial flow filed. Therefore, two stable flow fields can be formed at the same rotational speed and which one prevails depends on the flow history. The flow fields were measured using PIV and UVP, to explore the hysteresis range of four different xanthan gum solutions. The hysteresis range shifts toward higher rotational speed with increasing concentrations. The Reynolds number was failed to characterize the flow within hysteresis range but can be used for rotational speeds exceeding hysteresis range. The aim of this work was to introduce this phenomenon and to provide the first comparison between the two flow patterns and the fundamental for further researches dealing with the hysteresis effect in flow fields. [ABSTRACT FROM AUTHOR]

• For the first time the rheology of bioactive Pickering emulsions was investigated. • Addition of lipases changed the rheology from shear-thinning to Newtonian behavior. • The effect of lipases was outweighed by increasing the nanoparticle concentration. • The effect of lipases was outweighed by increasing the dispersed phase fraction. • Essential knowledge for fluid dynamic design of equipment and for process operation. The use of Pickering emulsions for biocatalytical applications has recently received increased attention in cases where hydrophobic reactants are involved. For process applications, knowledge of the emulsion's rheology is crucial for the fluid dynamical design of equipment and selection of operating conditions. Colloidal silica nanoparticle stabilized Pickering emulsions usually exhibit shear-thinning behavior caused by a complex particle-particle network. While this has been observed by many authors, no publication has yet dealt with the rheology of silica nanoparticle stabilized Pickering emulsions containing enzymes. Thus, the aim of this study was to investigate the impact of the commonly used biocatalyst lipase (type and concentration), the dispersed phase volume fraction and the silica particle concentration on the rheological behavior of water-in-oil Pickering emulsions. For this purpose, the impact of the named parameters on the viscosity curves were measured. Lipases reduced the viscosities and transferred the rheological behavior from shear-thinning to Newtonian, which might be due to interactions of the lipase molecules via the formation of intermolecular disulfide bonds, which disturb the hydrogen-bond based silica particle-particle network. However, by increasing the dispersed phase volume fraction or the silica particle concentration the rheological behavior of emulsions became again shear-thinning. This work will help to produce bioactive Pickering emulsions with tailor-made characteristics. [ABSTRACT FROM AUTHOR]

The authors present a new algorithm for analyzing ray deflection within spherical refractive index fields. The algorithm emanates from the well-known deconvolution algorithm for axisymmetric refractive index fields using the inverse Abel transformation and can be used for experimental Rainbow Schlieren Deflectometry (RSD) data. It was numerically validated by Computational Fluid Dynamics (CFD) calculations of free convection around an isothermal sphere and successive ray tracing through the determined temperature field. The algorithm determined radial temperature profiles and local Nusselt numbers from resulting deflection angles of the ray tracing simulations. An excellent agreement between original and reconstructed temperature field within the limits of assumptions was reached. This proves the usability of the algorithm for the experimental determination of spherical refractive index fields from future heat or mass transfer experiments. [ABSTRACT FROM AUTHOR]

No abstract. [ABSTRACT FROM AUTHOR]

Highlights from the article: Been published in this field, new developments in measuring techniques and numerical models lead Workshops were printed in proceedings. Copyright of Chemical Engineering & Technology is the property of John Wiley & Sons, Inc.

The application of compact NMR instruments to hot flowing samples or exothermically reacting mixtures is limited by the temperature sensitivity of permanent magnets. Typically, such temperature effects directly influence the achievable magnetic field homogeneity and hence measurement quality. The internal‐temperature control loop of the magnet and instruments is not designed for such temperature compensation. Passive insulation is restricted by the small dimensions within the magnet borehole. Here, we present a design approach for active heat shielding with the aim of variable temperature control of NMR samples for benchtop NMR instruments using a compressed airstream which is variable in flow and temperature. Based on the system identification and surface temperature measurements through thermography, a model predictive control was set up to minimise any disturbance effect on the permanent magnet from the probe or sample temperature. This methodology will facilitate the application of variable‐temperature shielding and, therefore, extend the application of compact NMR instruments to flowing sample temperatures that differ from the magnet temperature. [ABSTRACT FROM AUTHOR]

The productivity of Aspergillus niger cultivations is strongly linked to the pellet morphology. In this article, the agitation‐ and aeration‐induced stress on bio agglomerates is studied. To facilitate investigations, non‐biological particle systems are extensively used to model the actual biological matter. The literature lacks a direct comparison of model systems with the biological system of interest, leaving uncertainties in the applicability of such systems. This work shows that the results for the impellers' stress intensity of three A. niger strains agree qualitatively with the ones of four developed model systems of different nature (s/l, l/l). The findings justify the usage of model systems, despite certain limitations originating from their specific characteristic properties. [ABSTRACT FROM AUTHOR]

The effect of the feeding conditions and operating temperatures on the separation process was investigated in a continuous gravity-driven separator, following the analysis of the outlet drop size, and formation/shape of dense-packed zone. The inlet and outlet drop size distributions (DSDs) were considered in combination with the separation efficiency. The inlet and outlet DSDs were found to be self-similar across varied feeding conditions and operating temperatures. An increase of operating temperatures from 20 to 40 ∘C had a tiny impact on the inlet DSDs and resulted in an 1% - 3% increase in separation efficiency but an 8% - 13% reduction in outlet drop size. A novel concept of integrating separation efficiency and DSDs was introduced, allowing for a more comprehensive assessment of the separation process. The fractional separation efficiency was introduced, and it was evaluated based on the self-similarity of inlet and outlet DSDs. • Effect of feeding conditions and operating temperatures on separation was studied. • Both inlet and outlet DSDs were found to be self-similar. • Separation efficiency was combined with inlet and outlet DSDs. • Self-similarity was used to calculate fractional separation efficiency. [ABSTRACT FROM AUTHOR]

Multi-objective optimizations are performed for single and dual-impeller systems. The steady-state mean age theory approach with a novel method developed in previous work is applied for mixing time prediction. The three-blade Pitched-blade turbines are the baseline designs. The study aims to find the optimum impellers with lower mixing time and power consumption than the benchmark designs. The blade consists of two parts characterized by 10 to 12 design parameters, and 120 designs are investigated during optimization. The parameter analysis study highlights that the angle formed by the line connecting the two parts is the most critical parameter affecting mixing performance and power input in both systems. Compared to the baseline design, experimental results show that the optimum designs from single and dual impeller optimization reduce the power consumption 10% and 35%, respectively. However, the reduction in mixing time is not significant. Designs that have lower power numbers with higher power input reduce mixing times by 20%–30%. • The connection line angle affects mixing performance and power input significantly. • Pareto plots are obtained from optimization studies with SHERPA algorithm. • The reliability of the mean age theory approach in optimization study is confirmed. • Optimum designs decrease power by 10% and 35% with no distinct decreases on mixing. • Designs with low power numbers but high power input significantly reduce mixing time. [ABSTRACT FROM AUTHOR]

No abstract. [ABSTRACT FROM AUTHOR]

The impact of the static friction coefficient, the initial particle orientation, and the particle height‐to‐diameter ratio on the bed voidage of random packings with a low tube‐to‐particle diameter ratio is investigated for spherical and cylindrical particles using the discrete element method. Based on the numerical results a correlation is proposed to predict the bed voidage as a function of the static friction coefficient and the tube‐to‐particle diameter ratio for spheres, equilateral and non‐equilateral cylinders. This correlation is extended for the use of hollow cylinders. [ABSTRACT FROM AUTHOR]

Drop size distributions and phase separation behavior of water‐oil‐nonionic amphiphile systems are investigated using an in situ endoscope measurement technique and an external camera in stirred tanks in batch mode. The fitting procedure and the simulation results of a phase separation model are analyzed under the condition that either the swarm sedimentation speed or the mean drop size during sedimentation is known. The steady‐state drop size distributions are self‐similar over the whole range of process parameters, but not in the decaying turbulence field after agitation stop. The coalescence rate in the first seconds after agitation stop clearly affects the separation behavior, so that a prediction of the separation time based on the initial conditions in steady state is not trivial. [ABSTRACT FROM AUTHOR]

Highlights • Lignin and hemicellulose sugar uptake by four polymeric resins and one zeolite. • Single- and multi-component isotherms were determined of the two best adsorbents. • Freundlich and extended Freundlich isotherm provided the best fitting for lignin. • Langmuir and extended Freundlich isotherm provided the best fitting for hemicellulose. • Adsorbed lignin/hemicellulose were desorbed with 90%/100% using 50 wt% ethanol. Abstract Separation of lignin from hemicellulose sugar out of beech wood hydrolysate (BWH) by four polymeric and one zeolitic adsorbents was investigated. First, by means of single and binary model solutions (MS), consisting of 3.1 g/L phenol and/or 4.2 g/L xylose, the two most suitable adsorbents were chosen and single- and multi-component isotherms were determined. Second, the isotherm model parameters from the MS were applied to the equilibrium measurements of BWH and statistically evaluated regarding their adaptability. All experiments were carried out in batch mode. Of the five tested adsorbents, Amberlite XAD7HP and SEPABEADS SP700 were found to be the most efficient. Phenol and lignin removal was 100% and over 93% respectively and xylose and hemicellulose sugar recovery was greater 92% at an adsorbent-to-solution ratio of 1:5 w/v (g/mL). Phenol adsorption agreed best to Freundlich equation and xylose adsorption to Langmuir equation for XAD7HP and SP700 in the single-component experiments. In a multi-component system, adsorption behavior of both phenol and xylose for the two adsorbents can be fitted best to an extended Freundlich isotherm. For practical applications, it is reasonable to use Freundlich and extended Freundlich isotherms for xylose adsorption onto XAD7HP and SP700. Application and evaluation of the isotherm model parameters determined by the MS to the equilibrium data from adsorption experiments of BWH onto XAD7HP and SP700 showed that the valid isotherm type and thus the predominant adsorption mechanisms can be predicted accurately. However, the isotherm model parameters of the MS do not adequately describe the specific adsorption process of the BWH onto the resins. Hence, they have to be determined individually. More than 90% of adsorbed lignin and 95% of adsorbed hemicellulose sugar were desorbed using 50 wt% ethanol solution. [ABSTRACT FROM AUTHOR]

The influence of feeding conditions on outlet drop sizes, dense-packed zone, and separation efficiency of a liquid-liquid gravity separator was investigated experimentally. A continuously stirred tank was used to adjust the inlet drop size independent of other feeding conditions, such as flow rate and dispersed phase fraction. The inlet drop size, thereby, is one of the key parameters determining separation efficiency. The outlet drop size was, for the first time, studied in detail and showed a strong association with separation efficiency. The dimension and shape of the dense-packed zone in the separator were determined. With rising inlet drop sizes, a morphological transition of the dense-packed zone from full-length to a trapezoidal shape, wedge shape, and eventually to its complete disappearance was observed. The critical outlet drop sizes were determined with four sedimentation models as a function of feeding conditions, and optimal feeding conditions of the separator were identified. • Separation in a liquid-liquid settler was studied with varied feeding conditions. • Inlet drop size determined the formation and shape-transition of dense-packed zone. • Outlet drop size and dispersed phase fraction was linked with separation efficiency. • Separation efficiency and optimal feeding condition were determined. [ABSTRACT FROM AUTHOR]

Human adipose tissue-derived stromal/stem cells (hASCs) are a valuable source of cells for clinical applications, especially in the field of regenerative medicine. Therefore, it comes as no surprise that the interest in hASCs has greatly increased over the last decade. However, in order to use hASCs in clinically relevant numbers, in vitro expansion is required. Single-use stirred bioreactors in combination with microcarriers (MCs) have shown themselves to be suitable systems for this task. However, hASCs tend to be less robust, and thus, more shear sensitive than conventional production cell lines for therapeutic antibodies and vaccines (e.g., Chinese Hamster Ovary cells CHO, Baby Hamster Kidney cells BHK), for which these bioreactors were originally designed. Hence, the goal of this study was to investigate the influence of different shear stress levels on the growth of humane telomerase reversed transcriptase immortalized hASCs (hTERT-ASC) and aggregate formation in stirred single-use systems at the mL scale: the 125 mL (=SP100) and the 500 mL (=SP300) disposable Corning® spinner flask. Computational fluid dynamics (CFD) simulations based on an Euler-Euler and Euler-Lagrange approach were performed to predict the hydrodynamic stresses (0.06-0.87 Pa), the residence times (0.4-7.3 s), and the circulation times (1.6-16.6 s) of the MCs in different shear zones for different impeller speeds and the suspension criteria (Ns1u, Ns1). The numerical findings were linked to experimental data from cultivations studies to develop, for the first time, an unstructured, segregated mathematical growth model for hTERT-ASCs. While the 125 mL spinner flask with 100 mL working volume (SP100) provided up to 1.68 × 105 hTERT-ASC/cm² (=0.63 × 106 living hTERT-ASCs/mL, EF 56) within eight days, the peak living cell density of the 500 mL spinner flask with 300 mL working volume (SP300) was 2.46 × 105 hTERT-ASC/cm² (=0.88 × 106 hTERT-ASCs/mL, EF 81) and was achieved on day eight. Optimal cultivation conditions were found for Ns1u < N < Ns1, which corresponded to specific power inputs of 0.3-1.1 W/m³. The established growth model delivered reliable predictions for cell growth on the MCs with an accuracy of 76-96% for both investigated spinner flask types. [ABSTRACT FROM AUTHOR]