Wärmeübergang und Druckverlust wässeriger Tensidlösungen an einer querangeströmten berippten Rohrwendel

Zusammenfassung Durch Zugabe geeigneter Reibungsminderer in das Wasser von Fernw?rmenetzen kann der auftretende Druckverlust betr?chtlich gesenkt und somit die ben?tigte elektrische Antriebsenergie der F?rderpumpen reduziert werden. Neu entwickelte Tensidsysteme erfüllen die Anforderungen der Fernw?rmepraxis an die thermische und mechanische Belastbarkeit. Ein wichtiger Aspekt ist dabei die Beeinflussung des W?rmeüberganges in den für Fernw?rmenetze gebr?uchlichen W?rmeübertragern. In früheren Arbeiten wurden der W?rmeübergang und der Druckverlust w?sseriger Tensidl?sungen in geraden Rohren und in Rohrwendeln untersucht. Aufbauend auf diesen Erkenntnissen werden in dieser Arbeit der W?rmeübergang und der Druckverlust w?sseriger Tensidl?sungen bei umstr?mten Rippenrohren, wie sie bei Brauchwassererw?rmern auftreten, untersucht. Das Ziel ist die Darstellung und Beschreibung der auftretenden Effekte beim Einsatz solcher L?sungen, wobei aufgrund der komplexen Str?mungszust?nde bisher keine Berechnungsgleichungen entwickelt werden konnten.     

Studies on the lithium transport across the red cell membrane. I. Li+ uphill transport by the Na+-dependent Li+ counter-transport system of human erythrocytes

Li+ net-transfer across cell membranes was studied on human erythrocytes and ghosts preloaded with 1-2 mM Li+ and incubated in saline media of varying composition at initial thermodynamic equilibrium for Li+. The following results were obtained: 1. Li+ is extruded from glycolyzing erythrocytes against an electrochemical gradient until a steady-state Li+ distribution is established after 24-28 h. 2. The initial rate of Li+ extrusion is not altered by ouabain or by reduction of ATP levels to less than 25% of the normal value. 3. Replacement of external Na+ by K+ or choline+ abolishes the establishment of an electrochemical Li+ gradient. 4. The Li+ distribution ratio Lie+/Lii+ increases proportional to the ratio Nae+/Nai+ at constant extravellular K+ concentrations. 5. In ghost suspension an uphill Li+ transport is driven by an oppositely directed Na+ gradient. The direction of the Li+ uphill transport can be reversed by reversing the Na+ gradient. From the results it is concluded that the Li+ uphill transport across human red cell membranes is mediated by a Na+-dependent Li+ counter-transport system. This system is not inhibited by ouabain and does not appear to be identical to the Na+-Na+ exchange system described by Garrahan and Glynn.     

Verfahren zur Herstellung von hochwertigen Spanplatten in Klein-Anlagen

Zusammenfassung Den Verfassern war die Aufgabe gestellt, die schon oft er?rterte Frage der Abfallverwertung in Gro?s?gewerken durch Errichtung eines im Verbund zu betreibenden Spanplattenwerkes zu l?sen. Die technischen, betrieblichen und wirtschaftlichen Voraussetzungen hierzu werden geschildert. Es wird ein überblick über technische Einzelheiten des neu erstellten Spanplattenwerkes gegeben. Arbeitskr?ftebedarf, W?rme und Leimverbrauch sowie die technologischen Eigenschaften der erzeugten Spanplatten sind aufgeführt und erl?utert.

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Procedure for the manufacture of high-quality particleboard in small plants

Summary The authors were presented with the task of solving the problem of waste utilization in large-scale sawmills by erecting a threeshift particleboard plant. The respective technical, operating, and economic pre-conditions are discussed. A survey is given on technical details of the newly established particleboard plant. Manpower demand, heat, and glue consumption as well as the technological properties of the particle-boards produced are named and discussed.

     

Surface characterization of flax,hemp and cellulose fibers; Surface properties and the water uptake behavior

The surface characteristics of several natural fibers—flax, hemp and cellulose—were investigated using scanning electron microscopy, BET-surface area and zeta (ζ-) potential measurements. ζ-Potential measurements using the streaming potential method were performed in order to study the water uptake behavior as well as the surface properties of several natural fibers. The influence of different flax-fiber separation methods and several modifications, like industrial purification, and such a treatment followed by alkaline purification as well as polypropylene grafting on the fiber surface morphology, surface area and time- and pH-depending ζ-potentials were studied. The time-dependence of the ζ-potential, measured in 1 mM KCl solution, offeres and alternative possibility to estimate the water uptake behavior for nearly all investigated natural fibers. The water uptake data derived from the ζ-potential measurements (ζ = f(t)) were compared with data from conventional water adsorption studies for some chosen examples.