Untersuchung der Verteilung und Intensität filamentierter Barrierenplasmen für die Behandlung von Oberflächen

The application of barrier discharges at atmospheric pressure in air expands on the market of plasma technology, because it is an ecological and cost‐effective alternative to other processes of surface treatment. These plasmas usually consist of a multitude of spatially and temporally localized filaments, whose distribution should be as even as possible for homogeneous treatment. This holds especially for the plasma treatment of sensitive goods such as wool or other textiles. In equipment for continuous pass of material the barrier arrangements often consist of a system cylinder – cylinder or cylinder – plane, whereby the gap width changes locally. Space distribution and intensity of filaments has been investigated by means of short‐time photography and spatially resolved measurement of current distribution and energy distribution derived from it. The local dependency found can be explained by means of a capacitive equivalent circuit.     

Crystallographic electron microscopy

We present a family of techniques for the transmission electron microscope that generate surface zone-axis patterns. These patterns display the variation of the diffracted-beam intensity as a function of the angle of the incident electrons. The conditions of the experiments are those of reflection high-energy electron diffraction at near grazing incidence. The techniques are: surface convergent-beam diffraction, a surface analogue of the Tanaka method and a modified double-rocking scheme. Experimental results are presented for diffraction from surfaces of MgO and MoS₂. We anticipate that surface zone-axis patterns (surface ZAPs) will become established as an important tool for surface characterization, especially when used in conjunction with high-resolution surface imaging and surface energy loss spectroscopy; surface ZAPs may be expected to play, in surface analysis, a role analogous to that played by convergent-beam diffraction in normal transmission electron microscopy.     

Numerical analysis of IPIRG cracked pipe experiments subjected to dynamic and cyclic loading

This report contains results of a finite element study aiming to identify the influence of loading history and geometry for cracked pipes subjected to complex loading. The experiments have been performed within the International Piping Integrity Research Group (IPIRG) Program. The majority of the numerically analyzed experiments were conducted on straight pipes with an outside diameter of 168 mm and containing a large circumferential through-wall crack. The considered pipes were loaded in four-point bending under displacement control and at a temperature of 288°C. The types of loading were combinations of either quasi-static or dynamic and also monotonic or cyclic loading with different loading ratios R. Some analyses were also performed on surface-cracked pipes subjected to slow, monotonic loading.

In the finite element study, 20-node solid elements were used for the through-wall cracked pipes and a combination of shell and non-linear line spring elements for the surface-cracked pipes. Stable crack growth was simulated by gradual node relaxation and crack closure is accounted for by using simple contact elements. The J-integral for a remote contour is calculated and used as a characterizing fracture parameter although the cyclic loading violates the theoretical basis for this procedure. The near-tip J can not be used for growing cracks because of the weak energy singularity. The results of the numerical study confirm the trends from the experiments in that a high loading rate has a negative influence on the fracture properties of the studied carbon steel and that large cyclic loading, especially at R = −1, lowers the apparent J_R-curve for both carbon and stainless steels. To some extent geometry effects appear to be present when comparing the results from pipes containing surface cracks and through-wall cracks with results from CT specimens. These effects are more pronounced for large amounts of stable crack growth than at initiation.     

Zur Reaktivität von Tanninen in Abhängigkeit vom Kambialalter

Ohne Zusammenfassung     

Heat transfer and pressure drop in a new type of corrugated channels

An experimental investigation of heat transfer and pressure drop from a new type of corrugated channels is presented. The investigation has been carried out for Reynolds numbers in the range of $\text{800 <}\text{Re}\text{< 5000}$ for one corrugated and one smooth channel. It is found that the heat transfer from the corrugated channel is up to 3.5 times higher than for the smooth one. The pressure drop is however large (5 – 6 times the value of a smooth channel) and it is suggested that the corrugation height and length should be altered in order to balance the increases in heat transfer and pressure drop.