Atomized Spray Quenching as an Alternative Quenching Method for Defined Adjustment of Heat Transfer

In Atomized Spray Quenching, water is atomized to a fine spray by compressed air and sprayed onto the hot metallic surface. On the surface, the single drops partially evaporate. Afterwards they are taken away by the superposed airflow. Thus a water film cannot form. By quenching one edge, it is shown that an undefined water film collapses at the edges and corners; roughness, as known from Water Spray Quenching, does not occur. In this way a defined adjustment of heat transfer including quality improvement is possible. The influence of impingement density, spray characteristics, drop velocity, drop diameter and surface temperature on heat transfer was investigated. The heat transfer was measured with infrared thermography. The spray characteristics were measured with a combination of 2D‐Phase‐Doppler‐Anemometer and Patternator. Heat transfer coefficients up to 3000 W/(m² K) were measured.     

Percolative current flow in high-Jc,polycrystalline high-Tc superconductors

In this article, experiments designed to ascertain the percolative nature of current flow in high critical-current density (J_c) polycrystalline superconductors are reviewed. A direct correlation between the grain-orientation texture with current transport in high-J_c TlB₂Ca₂Cu₃O_x thick films and Bi₂Sr₂Ca₂Cu₃O_x powder-in-tube tapes is obtained. Magnetooptical visualization of the current flow in the same regions confirms the percolative nature of current flow. Furthermore, numerical modeling of the current flow based on the observed grain boundary character distribution and the effects of the grain boundary misorientation angle on (J_c) was found to predict the percolative nature of current flow. These studies indicate that in order to increase the (J_c) further, increased fractions of small-angle boundaries are required and, hence, provide a research direction for the next generation of high-temperature superconducting wire.     

Synthesewettlauf zum Epibatidin,einem neuartigen Naturstoff mit hoher analgetischer Wirkung

The Epibatidine Competition: Synthetic Work on a Novel Natural Analgetic Epibatidine was isolated in 1992 from a South American poison frog. It has a unique structure among natural products, and its analgetic activity surpasses that of morphine up to 500 fold. Pharmacological interest in epibatidine focusses also on the fact that its mode of action is different from that of morphine. 10 independent syntheses were published in 1993/1994. They are compared here demonstrating the interaction of classical and modern synthetic methods.     

Mean residence time and hold-up of solids in rotary kilns

The influence of operational variables on the mean residence time (MRT) and hold-up of the solids in rotary kilns has been investigated by many researchers. However, their reports on the influence of the feed rate on MRT, for example, are not consistent with one another. In this study, experiments are conducted on a 400 mm ID pilot kiln with a cylindrical discharge dam. Sand is used as the testing solids. MRT and the hold-up are measured under various feed rates and rotation speeds. Experimental results indicate that MRT increases slightly with the feed rate, and that the gradient is smaller at high rotation speeds. The hold-up shows a near-linear increase with the mass of feed per kiln rotation. The experimental data are then used to test equations provided by different researchers for the prediction of MRT. Comparisons show that, results of the empirical equation from Sullivan, J.D., Maier, C.G., Ralson, O.C. [1927. Passage of solid particles through rotary cylindrical kilns. U.S. Bureau of Mines Technical Paper No. 384.] agree well with measurements for the cases of low kiln loadings, while the numerical model of Saeman, W.C. [1951. Passage of solids through rotary kilns: factors affecting time of passage. Chemical Engineering Progress 47, 508-514.] gives good predictions over the entire range of parameters considered.     

<Emphasis Type="Italic">In-situ</Emphasis> observations of lattice parameter fluctuations in austenite and transformation to bainite

The isothermal transformation of high-carbon austenite-to-bainitic ferrite has been investigated with the in-situ technique of time-resolved X-ray diffraction using synchrotron radiation. The measurements indicate that prior to transformation, the austenite divided into regions with significantly different lattice parameters. It is possible that this is due to the development of carbon-rich and carbon-poor regions in the austenite, as a precursor to transformations including the bainite reaction. The lattice parameter became uniform as transformation progressed and the fraction of carbon-poor austenite decreased. The ferrite itself exhibited a large range of lattice parameters during the early stages of transformation, due to the trapping of carbon.     

Über den Anwendungsbereich von stabilisiertem Zirkondioxyd als Feststoffelektrolyt zur elektrochemischen Sauerstoffbestimmung in flüssigem Eisen

Einschränkung des Anwendungsbereiches durch Elektronenleitung sowie durch Gasdurchlässigkeit des Elektrolyten bei hohen Temperaturen bei Verwendung von Luft als Sauerstoffbezugspotential. Beschreibung einer Meßzelle zur kontinuierlichen elektrochemischen Sauerstoffbestimmung mit handelsüblichem stabilisiertem Zirkondioxyd und Chrom/Chrom(III)-oxyd als Sauerstoffbezugspotential     

Mathematisches Modell zur Koksvergasung

Beschreibung eines mathematischen Modells für die Vergasung von stückigem Koks in einer CO₂-CO-N₂-Atmosphäre mit Erfassung aller wesentlichen stofflichen und energetischen Teilschritte wie Diffusion, Wärmeleitung, Stoff- und Wärmeübergang. Untersuchung der Geschwindigkeit der Phasengrenzreaktion und deren Beeinflussung durch Alkalien. Überprüfung des mathematischen Modells durch Laboratoriumsmessungen. Erörterung der Einflüsse von Temperatur, Gaszusammensetzung, Stückgröße und Alkaligehalt.