Effect of external turbulence on the efficiency of film cooling with coolant injection into a transverse trench

Film cooling is among the basic methods used for thermal protection of blades in modern high-temperature gas turbines. Results of computer simulation of film cooling with coolant injection via a row of conventional inclined holes or a row of holes in a trench are presented in this paper. The ANSYS CFX 14 commercial software package was used for CFD-modeling. The effect is studied of the mainstream turbulence on the film cooling efficiency for the blowing ratio range between 0.6 and 2.3 and three different turbulence intensities of 1, 5, and 10%. The mainstream velocity was 150 and 400 m/s, while the temperatures of the mainstream and the injected coolant were 1100 and 500°C, respectively. It is demonstrated that, for the coolant injection via one row of trenched holes, an increase in the mainstream turbulence intensity reduces the film cooling efficiency in the entire investigated range of blowing ratios. It was revealed that freestream turbulence had varied effects on the film cooling efficiency depending on the blowing ratio and mainstream velocity in a blade channel. Thus, an increase in the mainstream turbulence intensity from 1 to 10% decreases the surface-averaged film cooling efficiency by 3–10% at a high mainstream velocity (400 m/s) in the blade channel and by 12–23% at a moderate velocity (of 150 m/s). Here, lower film cooling efficiencies correspond to higher blowing ratios. The effect of mainstream turbulence intensity on the film cooling efficiency decreases with increasing the mainstream velocity in the modeled channel for both investigated configurations.     

Young’s modulus of low-pressure cold sprayed composites: an analysis based on a minimum contact area model

A theoretical and mathematical model based on minimum contact area (MCA) is developed to explain the bonding that takes place in the low-pressure gas dynamic spray (LPGDS) process. It is shown that by normalizing this MCA it is possible to compare the relative elastic modulus as a function of porosity. Theoretical predictions of relative elastic modulus are compared against results obtained through acoustic analysis and it is found that the correlation between is dependent on the porosity. For low porosity, the experimental and theoretical results differ substantially, while for higher porosity there seems to be good agreement between the two. To explain this behaviour it is theorized that full adiabatic shear bands (ASB) are created between only some of the particles. The higher porosity causes higher strain in the samples and thus more local deformation of the particles. This, in turn, causes more actual ASB formation. Since the theoretical model assumes full ASB formation, only the higher porosities cause enough strain to have a comparable relative elastic modulus. For the lower porosities, the local strain is less, and some of the bonds will not achieve full ASB formation. For these cases, the relative elastic modulus will be lower than that predicted.     

Differential detection of enantiomeric gaseous analytes using carbon black-chiral polymer composite, chemically sensitive resistors

Carbon black-chiral polymer composites were used to provide diagnostic differential resistance responses in the presence of enantiomers of chiral gaseous analytes. Vapors of (+)-2-butanol and (-)-2-butanol, (+)-α-pinene and (-)-α-pinene, (+)-epichlorohydrin and (-)-epichlorohydrin, and methyl (+)-2-chloropropionate and methyl (-)-2-chloropropionate were generated and passed over a chemically sensitive carbon black-poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate) (77% butyrate) composite resistor. Each enantiomer of a pair produced a distinct relative differential resistance change on the chiral detector, whereas both enantiomers of a set produced identical signals on achiral carbon black-poly(ethylene-co-vinyl acetate) (82% ethylene) detectors.     

Managing the complexity of digital transformation—How multiple concurrent initiatives foster hybrid ambidexterity

Incumbent companies are launching digital transformation initiatives (DTIs) to cope with technological changes, challenging competitive environments, increasing customer demands, and other digitalization challenges. The DTI spectrum is broad and covers structural and contextual changes. Companies often launch multiple. concurrent DTIs, resulting in considerable organizational complexity. However, there has been very little research into the successful management of the interplay between DTIs. Drawing on five management aspects (strategic alignment, governance, methods/IT, people, and culture) and insights from three case companies, we elucidate DTIs’ interplay, illustrating that beneficial DTI interplay management leads to a complementary duality instead of a competing dualism in organizational ambidexterity. We explicate that multiple concurrent DTIs can foster structural and contextual ambidexterity, which leads to hybrid ambidexterity, concluding that contextual ambidexterity coheres and balances exploration and exploitation efforts. Thereby, we contribute to a better understanding of DTIs, their interplay management, and their roles to foster hybrid ambidexterity.

     

Trends in odor intensity for human and electronic noses: relative roles of odorant vapor pressure vs. molecularly specific odorant binding

Response data were collected for a carbon black-polymer composite electronic nose array during exposure to homologous series of alkanes and alcohols. The mean response intensity of the electronic nose detectors and the response intensity of the most strongly driven set of electronic nose detectors were essentially constant for members of a chemically homologous odorant series when the concentration of each odorant in the gas phase was maintained at a constant fraction of the odorant's vapor pressure. A similar trend is observed in human odor detection threshold values for these same homologous series of odorants. Because the thermodynamic activity of an odorant at equilibrium in a sorbent phase is equal to the partial pressure of the odorant in the gas phase divided by the vapor pressure of the odorant and because the activity coefficients are similar within these homologous series of odorants for sorption of the vapors into specific polymer films, the data imply that the trends in detector response can be understood based on the thermodynamic tendency to establish a relatively constant concentration of sorbed odorant into each of the polymeric films of the electronic nose at a constant fraction of the odorant's vapor pressure. Similarly, the data are consistent with the hypothesis that the odor detection thresholds observed in human psychophysical experiments for the odorants studied herein are driven predominantly by the similarity in odorant concentrations sorbed into the olfactory epithelium at a constant fraction of the odorant's vapor pressure.     

A superconducting beta spectrometer

We have designed and constructed a superconducting beta spectrometer with a momentum resolution of about 2% and a peak solid angle of 0.5 sr. The performance of the spectrometer is described and the results of calibrations with line sources are presented.     

Nachweis von 2,3-Dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-on in Lebensmitteln

Zusammenfassung 2,3-Dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-on (1) wurde in verschiedenen erhitzten Lebensmitteln nachgewiesen. Es bildet sich beim Kochen von Karotten, Zwiebeln, Tomaten und Kohl sowie beim Erhitzen von Fleisch.1 entsteht auch bei der Karamellisierung von Mono- und Disacchariden; es findet sich daher in Karamelbonbons, gebrannten Mandeln und Brotkruste. Die Bildung wird durch primäre Amine, Aminosäuren und Eiweiß katalysiert.

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Proof of 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-on in foods

Summary 2,3-Dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-on is proved in various cooked food products. It is formed when carrots, onions, tomatoes, cabbage and meat are heated. It is also present in caramelized mono- and disaccharides, in caramel sweets and bread crusts. The formation of this compound is due to the catalytic effect of primary amines, amino acids and protein.