On the modelling of bubbly flow in vertical pipes

To qualify CFD codes for two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubbly flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. Applying a two fluid approach, besides the drag forces describing the momentum exchange in flow direction, the non-drag forces acting perpendicular to the flow direction play an important role for the development of the flow structure. Gas–liquid flow in vertical pipes is a very good object for studying the corresponding phenomena. Here, the bubbles move under clear boundary conditions, resulting in a shear field of nearly constant structure where the bubbles rise for a comparatively long time. The evolution of the flow within the pipe depends on a very complex interaction between bubble forces and bubble coalescence and break-up, e.g. the lift-force, which strongly influences the radial distribution of the bubbles, changes its sign depending on the bubble diameter. The consequence is the radial separation of small and large bubbles. Neglecting this phenomenon, models are not able to describe the correct flow structure. Extensive experiments measuring the radial gas volume fraction distribution, the bubble size distribution and the radial residence of bubbles dependent on their size were determined for different distances from the gas injection. Basing on these experiments the applicability and the limits for the simulation of bubble flow with current CFD-codes are demonstrated, using the simulation of vertical pipe flow with CFX-4 as an example. Using a simplified model focusing particularly on the radial phenomena described above, parametric studies were conducted. They give an indication for necessary improvements of the codes. Finally a possible way for the improvement of the CFD-codes is shown.     

Untersuchungen zur Haftungsbeeinflussung von Pigmentdrucken durch UV-Laser-Behandlung

Investigations on Adhesion of Pigment Printings by UV-Laser Treatment Investigations on the influence of UV-laser treatment of polyethyleneterephthalate and polyamide fibers and foils on the adhesion properties of pigment printings are presented. It could be shown that even irradiation with low energy densities and low number of pulses applied increases binder film adhesion very efficiently. Some interpretations of the laser action upon adhesion improvement related to surface modification are presented.     

Curcumin‐Derived Pyrazoles and Isoxazoles: Swiss Army Knives or Blunt Tools for Alzheimer's Disease?

Curcumin binds to the amyloid beta peptide (Abeta) and inhibits or modulates amyloid precursor protein (APP) metabolism. Therefore, curcumin-derived isoxazoles and pyrazoles were synthesized to minimize the metal chelation properties of curcumin. The decreased rotational freedom and absence of stereoisomers was predicted to enhance affinity toward Abeta(42) aggregates. Accordingly, replacement of the 1,3-dicarbonyl moiety with isosteric heterocycles turned curcumin analogue isoxazoles and pyrazoles into potent ligands of fibrillar Abeta(42) aggregates. Additionally, several compounds are potent inhibitors of tau protein aggregation and depolymerized tau protein aggregates at low micromolar concentrations.     

Chemical Structure of <Emphasis Type="Italic">Bacteriovorax stolpii</Emphasis> Lipid A

Bdellovibrionales is a phylogenetically diverse group of predatory prokaryotes, which consists of the two families Bdellovibrionaceae and Bacteriovoracaceae. We describe LPS and lipid A of the type strain Bacteriovorax stolpii DSM 12778, representing the first characterized endotoxin of a Bacteriovoracaceae member. It has a smooth form LPS, which was identified by SDS-polyacrylamide gel electrophoresis. The lipid A structure was determined by combined gas chromatography–mass spectrometry, electrospray ionization mass spectrometry and NMR spectroscopy. Its backbone consists of two β-(1 → 6)-linked 2,3-diamino-2,3-dideoxy-d-glucopyranoses (GlcpN3N) carrying a pyrophosphoethanolamine at O-4′ of the non-reducing sugar and a phosphate group linked to O-1 of the reducing GlcpN3N. Positions 2, 3, 2′ and 3′ of the two GlcpN3N are acylated with primary 3-hydroxy fatty acids and one of those carries a secondary fatty acid.     

Zerstörungsfreie Prüfung von Polymeren mittels photothermischer Meßmethoden. 2. Photoakustische untersuchungen von Polyesterfärbungen in Abhängigkeit von der Farbstoffkonzentration und der Oberflächenrauheit

The determination of dyestuff concentration in dark and saturated dyed textiles poses great problems to conventional analytical methods. In this work the use of photoacoustic spectroscopy as analytical tool is systematically investigated by comparing measurements of samples with different dyestuff concentrations. The experimental data can be fitted to a modified Kubelka-Munk function which shows a linear relationship to the dyestuff concentration in a wider range than the reflection spectroscopy. The influence of the surface structure to the photoacoustic signal is investigated.     

Mechanische Eigenschaften von Polyesterfasern bei kurzzeitiger Zugbeanspruchung, 1. Aufbau eines Meßplatzes für schnelle Zugbeanspruchung

The stress-strain behaviour of filament yarns has been determined by variation of strain rates from 10^?1 up to 10⁵%/s. Strain rates up to 10%/s are obtained with a tensile testing machine. The higher strain rates up to 10⁵%/s are obtained with an apparatus using a falling weight by variation of the height of fall and the length of the yarn. Because of the high-speed impact and time of strain/influence down to 10^?4 s together with the variation of the height of fall between 0,6 and 166 cm a profound discussion of errors is necessary.     

New correlation to predict the heat transfer coefficient during in-tube cooling of turbulent supercritical CO2

The Nusselt number variations of supercritical carbon dioxide during in-tube cooling are presented and discussed. Using data presented in this paper as well as prior publications, a new correlation to predict the heat transfer coefficient of supercritical carbon dioxide during in-tube cooling has been developed. The new correlation is presented in this paper. It is based on mean Nusselt numbers that are calculated using the thermophysical properties at the wall and the bulk temperatures, respectively. It is seen that the majority of the numerical and experimental values are within ±20% of the values predicted by the new correlation.     

Purification, characterization and functional cloning of inositol oxygenase from Cryptococcus

The enzyme inositol oxygenase (myo-inositol : oxygen oxidoreductase; E.C. 1.13.99.1) is a monooxygenase that converts inositol into glucuronic acid in the presence of molecular oxygen. This enzyme is integrated into a pathway leading to either degradation and energy production or the biosynthesis of precursors for polysaccharides. The enzyme was purified from the yeast Cryptococcus lactativorus by a five-step chromatography procedure. The purified enzyme shows a molecular mass of 37 kDa on SDS-PAGE, similar to the estimation of the size of the native enzyme determined by size exclusion chromatography. Peptides of the inositol oxygenase protein derived from a tryptic digest were sequenced de novo by nanoelectrospray tandem mass spectrometry. Using degenerate oligonucleotides, the corresponding gene was cloned from first strand cDNA. The open reading frame encodes a 315 amino acid polypeptide with a predicted molecular mass of 36.9 kDa. Inositol oxygenase is a single copy gene in C. lactativorus. It has close homologues in other fungi such as Cryptococcus neoformans and Neurospora crassa. Biochemical characterization of the enzyme showed a pH optimum of 6-6.5 and a temperature optimum of 30 degrees C. Myo-inositol is the only accepted substrate with a Km of ca. 5 mM. The enzyme contains a Fe-centre but the enzyme activity is resistant to KCN.