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The dispersive mass transport in rivers has been investigated to improve the predictability of transport scenarios in case of accidental pollutant spills. In particular, the influence of dead-water zones, as they are given by groin fields, on the transport characteristics in the main stream has been analyzed. A literature review of detailed map material from the rivers Rhine, Waal and Elbe has been performed, in order to plan representative laboratory experiments. Typical aspect ratios of the groin fields as well as typical inclination angles have been summarized. Based on these results, experiments have been performed in a laboratory flume equipped with schematized groins. Within theses experiments the aspect ratio, the inclination angles as well as the groin field volume has been varied. Due to the fact that the flow is very shallow and, therefore, quasi two-dimensional, the flow velocities have been determined at the water surface, using a Surface Particle-Image-Velocimetry-System that has been developed for that purpose. Additional measurements, using a two-dimensional Laser-Doppler-Velocimeter, have been performed for resolving the velocity distribution over the water depth. With the help of these measurements it was possible to determine the typical recirculating flows in the groin fields as well as the coherent, horizontal eddies in the mixing layer between dead-water zone and main stream, that are governing the mass exchange. The high spatial and temporal resolution of the surface PIV measurements made it possible to estimate also the mass exchange between groin field and main stream. With the help of Planar-Concentration-Analysis, which is a method for determining depth-averaged planar concentration fields, it could be shown that the mass exchange between groin field and main stream increases with increasing length of the groin field. For these measurements a tracer injection device has been developed, that consists of a movable multi-port injection-box and vacuum-pressure-unit, which is able to produce instantaneously, homogeneous and reproducible concentration fields. Finally a Lagrangian-Particle-Tracking-Method was developed to transfer the results, obtained locally at single groin fields, into the overall transport characteristics in the far-field of pollutant spill scenario for a river system consisting of a series of groin fields. Through the implementation of a transient-adhesion-boundary, it was possible to parameterize the influence of groin fields on the longitudinal dispersion, the transport velocity and the skewness of the concentration distribution in the case of a pollutant spill.

pollutant transport --- Groin fields --- Lagrangian particle tracking --- dispersion

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The dispersive mass transport in rivers has been investigated to improve the predictability of transport scenarios in case of accidental pollutant spills. In particular, the influence of dead-water zones, as they are given by groin fields, on the transport characteristics in the main stream has been analyzed. A literature review of detailed map material from the rivers Rhine, Waal and Elbe has been performed, in order to plan representative laboratory experiments. Typical aspect ratios of the groin fields as well as typical inclination angles have been summarized. Based on these results, experiments have been performed in a laboratory flume equipped with schematized groins. Within theses experiments the aspect ratio, the inclination angles as well as the groin field volume has been varied. Due to the fact that the flow is very shallow and, therefore, quasi two-dimensional, the flow velocities have been determined at the water surface, using a Surface Particle-Image-Velocimetry-System that has been developed for that purpose. Additional measurements, using a two-dimensional Laser-Doppler-Velocimeter, have been performed for resolving the velocity distribution over the water depth. With the help of these measurements it was possible to determine the typical recirculating flows in the groin fields as well as the coherent, horizontal eddies in the mixing layer between dead-water zone and main stream, that are governing the mass exchange. The high spatial and temporal resolution of the surface PIV measurements made it possible to estimate also the mass exchange between groin field and main stream. With the help of Planar-Concentration-Analysis, which is a method for determining depth-averaged planar concentration fields, it could be shown that the mass exchange between groin field and main stream increases with increasing length of the groin field. For these measurements a tracer injection device has been developed, that consists of a movable multi-port injection-box and vacuum-pressure-unit, which is able to produce instantaneously, homogeneous and reproducible concentration fields. Finally a Lagrangian-Particle-Tracking-Method was developed to transfer the results, obtained locally at single groin fields, into the overall transport characteristics in the far-field of pollutant spill scenario for a river system consisting of a series of groin fields. Through the implementation of a transient-adhesion-boundary, it was possible to parameterize the influence of groin fields on the longitudinal dispersion, the transport velocity and the skewness of the concentration distribution in the case of a pollutant spill.

pollutant transport --- Groin fields --- Lagrangian particle tracking --- dispersion

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Particle velocimetry is a non-intrusive optical measurement method whereby global velocity fields can be obtained in either two- or three-dimensions through time by inferring fluid motion through the displacement of particle tracers which seed the flow. While particle image velocimetry (PIV), which obtains each velocity vector by tracking groups of particles within an interrogation window through a cross-correlation algorithm, has thrived generously since its development, particle tracking velocimetry (PTV), which obtains each of the velocity vector by tracking individual particle, has received less attention. The goal of this book is to therefore provide a review of PTV, with a focus on methods and techniques that have been implemented towards its development and improvement, rather than on its applications.

Particle tracking velocimetry. --- Particle image velocimetry. --- Flow, turbulence, rheology. --- SCIENCE / Mechanics / Hydrodynamics.

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Zentrifugal-Partikelreceiver stellen eine neuartige Komponente für die konzentrierende solare Energiegestehung (CSP) dar. Sie werden in punktfokussierenden CSP-Kraftwerken eingesetzt und gehören - im Gegensatz zu den bereits im Markt befindlichen indirekt absorbierenden Rohrreceivern - der Gruppe der direktabsorbierenden Receiver an. Als Wärmeträgermedium wird hierbei Granulat genutzt, wie beispielsweise Bauxit-Proppants. Bauxit als Wärmeträgermedium ermöglicht höhere Prozesswirkungsgrade aufgrund von höheren Anwendungstemperaturen als in aktuell kommerziell eingesetzten, indirekt absorbierenden Systemen. Gleichzeitig ist Bauxit-Granulat als Wärmespeichermedium einsetzbar, da es besonders kostengünstig ist. Das Potential des Zentrifugal-Partikelreceiver wurde bereits erfolgreich in einem 15kWth Laborreceiver am Deutschen Zentrum für Luft- und Raumfahrt e.V. bewiesen. Darauf aufbauend verfolgt diese Arbeit das Ziel, die Strömungsmechanik von fließenden Granulaten zu modellieren.

Technology. --- Solarthermische Kraftwerke mit Strahlungsbündelung (CSP) --- Solarturmkraftwerke --- direkt absorbierende Receiver (DAR) --- Partikelreceiver --- particle tracking velocimetry (PTV)

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This Special Issue of Entropy, titled “Recent Advances in Single-Particle Tracking: Experiment and Analysis”, contains a collection of 13 papers concerning different aspects of single-particle tracking, a popular experimental technique that has deeply penetrated molecular biology and statistical and chemical physics. Presenting original research, yet written in an accessible style, this collection will be useful for both newcomers to the field and more experienced researchers looking for some reference. Several papers are written by authorities in the field, and the topics cover aspects of experimental setups, analytical methods of tracking data analysis, a machine learning approach to data and, finally, some more general issues related to diffusion.

Research & information: general --- Physics --- diauxic growth --- replicator equation --- mesoscopic model --- integro-differential equations --- anomalous diffusion --- statistical analysis --- single-particle tracking --- trajectory classification --- fractional Brownian motion --- estimation --- autocovariance function --- neural network --- Monte Carlo simulations --- multifractional Brownian motion --- power of the statistical test --- machine learning classification --- feature engineering --- confinement --- information theory --- Brownian particle --- stochastic thermodynamics --- CTRW --- diffusing-diffusivity --- occupation time statistics --- wound healing dynamics --- single pseudo-particle tracking --- phase contrast image segmentation --- 3D single-particle tracking --- Fisher information --- non-uniform illumination --- SPT --- deep learning --- residual neural networks --- random walk --- heterogeneous --- endosomes --- single particle trajectory --- stochastic processes --- trapping