Effective Parameter Interpretation and Extrapolation of Dispersion Simulations by Means of a Simple Two-Velocity Model

The investigation of dispersion by microscopic simulations yields a lot of detailed information. To identify characteristic behaviours, it is useful to condense this information into a few effective parameters, which describe the transport process in the model geometry on a larger scale. For this purpose, a very simple two-velocity model has been developed, which models the transition from reversible to irreversible spreading of a tracer volume. It is shown that this model is very similar to Taylor–Aris dispersion and that it is quite suitable to approximate the time dependence of dispersion. The model is applied to characterize the effect of dead end pores on dispersion with a single correlation parameter. Up to Péclet numbers of about 500, 'hold-up'-dispersion similar to Taylor–Aris-dispersion is found. The simulations have been performed by the lattice Bhatnagar–Gross–Krook (BGK) method, which is a particular type of cellular automata and therefore allows an easy implementation of complicated geometries. The fully irreversible asymptotic dispersion is reached in an exponential process, the parameters of which can be identified by the two-velocity model after the mixing has noticeably begun. These are used to extrapolate the process which reduces the computational effort by about one order of magnitude.     

A Theory for the Quantitative Estimation of Bed Load Transport Using Radioisotopes

In this paper an attempt has been made to develop a simple theory for the application of radiotracer techniques to estimate the quantum of bed material transported in rivers, estuaries, etc. The emphasis is mainly on the physical concepts involved. Certain assumptyions made in the theory are later verified experimentally.     

Teil I. Verweilzeit als zweidimensionale Zufallsvariable — Klassifikation der Alters- und Restverweilzeitverteilungsfunktionen

Die mit Hilfe radioaktiver Indikatoren meβbare Verweilzeit wird auf Grund des Stochastischen Charakters des Stofftransports in Strömungssystemen als Zufallsvariable dargestellt. Eine erweiterte Beschreibung der inneren Struktur von Strömungs-systemen führt zur Einteilung der Verweilzeit in Alter und Restverweilzeit. Beide Gröβen sind gleichfalls als Zufallsvariable aufzufassen, so daβ die innere Verweilzeitstruktur als zweidimensionaler Zufallsvektor beschrieben warden kann. Die ihm zugeordneten Verteilungsfunktionen warden als reine Ensemblefunktioen klassifiziert und am Schluβ der Arbeit tablelarisch zusammengefaβt. Die Betrachtungen bilden die Grundlage für die in Teil 2 Dargelegte physikalische und technologische Interpretation von Indikatorkonzentrationskurven.     

Experimentelle und theoretische Behandlung von Flüssig-Flüssig-Extraktionsgleichgewichten

Am Beispiel einer Kationenaustauschextraktion mit n-Caprylsäure werden die thermodynamische Behandlung von Extraktionsgleichgewichten dargelegt und die Methoden zur Auswertung experimenteller Ergebnisse diskutiert. Es wird über die Einsatzmöglichkeiten der Extraktionsapparatur AKUFVE bei derartigen Untersuchungen berichtet.     

Investigation of Moisture Migration in the Concrete of a Special Test Construction under Simulated Load Conditions

Investigations of the behaviour of water in the concrete of special constructions under load conditions are essential for judging safety aspects especially when the concerto is enclosed between liners. The injection of tritiated water of 60 Ci into the fresh concrete of the dome range of a test construction, sampling and sample preparations are described. The test results obtained again demonstrate the unique possibilities of the tracer technique with radionuclides in the investigation of local and temporal distributions of substances under complicated actual conditions.     

Electrochemical Studies of Polymeric Carbons. II. Surface Layer Formation on Glassy Carbon Electrodes in Chloride Solutions as Studied by Radiotracer Techniques

The interaction of chloride ions with glassy carbon electrodes is studied by means of ³⁶Cl as radiotracer. Chloride ions are bonded on the electrode in case of anodization depending on electrode potential and duration of the polarization. Strong interaction is observed at electrode potentials more positive than +1.3 V. A significant part of the chloride ions bonded at the glassy carbon can not be displaced neither by cathodic polarization nor by rinsing with water or non-labelled solutions. It is concluded that chloride ions are chemically bonded at the surface and the surface region of glassy carbon.     

Cost Benefit Ratio of Industrial Tracer Applications

Simple relations are given, which could help to estimate the expected annual savings resulting from the application of radioisotope methods for the mixing time, segregation effect or residence time distribution determination. Criteria for estimation of benefit at optimum transition of the continuous production from one quality to another, criteria for estimate the benefits on basis of known holdup and for estimate of benefits resulting from knowledge of the distribution function of residence time and of the kinetics of chemical reaction are presented. Further are demonstrated two examples of evaluation of the economic effect of the results of a system analysis in chemical industry where beside the measurements od residence time distribution by help of radiotracers are used also results of other experimental methods and that practically without increasing production cost.     

Vergleich von kinetischen Daten des N-Stoffwechsels im Ganzkörper von Läufern und Läuferinnen

Mil Hilfe der ¹⁵N-Tracertechnik wurde der N-Stoffwechsel von je 6 Läufern und Läuferinnen charakterisiert. Als Tracersubstanz wurde [¹⁵N]Glycin eingesetzt. Die tracerkinetischen Daten, die sich aus der Ausscheidung des lsotops im Urin ergeben, wurden unter Verwendung der Priming-Technik vermittelt. Die Parameter dcs Proteinstoffwechscls wurden auf der Grundlage eines 3-Pool-Stoffwechselmodells herechnet. Die experimentellen Ergebnisse werden diskutiert.

The N-metabolism of 6 male and 6 female runners are characterized with the help of the ¹⁵N tracer technique using [¹⁵N]glycine as a tracer substance. The tracer kinetic data coming from the excretion of the isotope in the urine were determined using the priming technique. The parameters of the protein metabolism were calculated on the basis of a 3-pool model. The experimental results are discussed.     

Cation self-diffusion and impurity diffusion in Fe2O3+

Cation self-diffusion D¹_Fe, parallel to the c axis has been measured as a function of temperature (1100–1300°C) and oxygen partial pressure p_o2 (2 × 10^?3-1 atm) in the same single crystals of Fe₂O₃ as those used by Chang and Wagner. Whereas the p_o2 dependence of D1_Fe, observed by Chang and Wagner has been confirmed, the absolute value of D¹_Fe and the activation enthalpy for self-diffusion are much higher than those reported by them. The various diffusion studies indicate that cation self-diffusion occurs by an interstitial-type mechanism. However, the sample-to-sample variations in D¹_Fe, suggest that all diffusion measurements may have been performed on samples where the defect concentrations are impurity controlled. Impurity diffusion of ⁶⁰Co, ⁵¹Cr, and ⁸⁸Y has also been measured as a function of p_o2 at 1200°C. The results indicate that these impurities diffuse by an interstitialcy mechanism in Fe₂O₃.