Tip-clearance and other three-dimensional effects in axial flow fans

Zusammenfassung Es wird die an einem Axialventilator durchgeführte Untersuchung der Auswirkung des Schaufelspaltes auf Laufradstr?mung und Leistung beschrieben. Das Laufrad, mit einem Durchmesser von 305 mm, war für ausgepr?gt dreidimensionale Str?mung entworfen. Die in solchen F?llen bestehenden Einschr?nkungen der Gültigkeit von zweidimensionalen Berechnungsunterlagen aus Windkanalversuchen werden besprochen. Es zeigte sich, dass die radial nach aussen gerichtete Querstr?mung durch Zentrifugalwirkung und die nach innen gerichtete Querstr?mung durch Vergr?sserung des Spaltspieles hervorgerufen wird. Vergr?sserung der Spaltweite beeinflusst die Str?mungsverh?ltnisse nicht nur in der N?he der Schaufelspitze, sondern über die ganze radiale Erstreckung der Schaufel. Dadurch wird die Druckziffer verkleinert, und die Abreissbedingungen ver?ndern sich. Unter diesen Verh?ltnissen ist es wesentlich, die ?nderung der Axialgeschwindigkeit im Laufrad korrekt in Rechnung zu setzen. Der wesentlichste Parameter scheint die Gr?ssec _2m /u zu sein. Dabei zeichnet sich bei gleichen Eintrittsverh?ltnissen, aber stark verschiedenen Querstr?mungen ein eindeutiger Zusammenhang zwischenc _2u /c _2m undc _2m /u für beliebige Schaufelgeometrien ab. Es mag daher von Vorteil sein, den aus Messungen am zweidimensionalen Windkanal erhaltenen Unterlagen in dieser Form den Vorzug vor den üblichen Einzelflügel- und Gitterparametern zu geben, die durch Querstr?mung merklich beeinflusst werden.      

Studies with dithizone: Part 33. effect of temperature on the spectrum in chloroform

The position and relative intensity of the two peaks in the visible absorption spectrum of dithizone dissolved in chloroform do not change on cooling from room temperature to ?48°C. Thus either the two absorption peaks cannot be ascribed to two discrete species (thiol and thione tautomers), or the enthalpy of their interconversion is zero.     

On using the weissenberg rheogoniometer to measure normal stresses in lubricating greases as examples of materials which have a yield stress

Summary Some years ago it was desired to measure normal stress components in viscometric flows of lubricating greases since it was thought that flow elasticity might be a relevant property in grease lubrication processes. An attempt at measurement was made with the cone-and-plate configuration of theWeissenberg rheogoniometer. Since greases are prone to fracture in this device the initial tests were carried out at very low rates of shear to avoid fracture. These tests revealed the existence of unusual effects which are ascribed to interactions between the instrument and the yield stress property. At high rates of shear it is possible to show the existence of normal stresses in greases but their measurement cannot be carried out accurately. Fracture and shear degradation occur; furthermore, the zero of the normal stress measurement is uncertain to within an amount proportional to the yield stress. Procedures for minimizing inaccuracies are discussed.

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Zusammenfassung Vor einigen Jahren entstand der Wunsch, die Normalspannungskomponenten in Schichtenströmungen (Viskosimeterströmungen) bei Schmierfetten zu messen, da man vermutete, daß die Elastizität eine wichtige Eigenschaft beim Schmierprozeß darstellen würde. Es wurde daher der Versuch unternommen, solche Messungen mit einer Kegel-Platte-Einrichtung imWeissenberg-Rheogoniometer durchzuführen. Da Schmierfette bei dieser Anordnung zum Bruch neigen, wurden die ersten Versuche bei sehr niedrigen Schergeschwindigkeiten gefahren. Diese Versuche erwiesen die Existenz von ungewöhnlichen Effekten, die der Wechselwirkung zwischen dem Gerät und Fließspannungs-Eigenschaften zuzuschreiben sind. Bei hohen Schergeschwindigkeiten ist es möglich, die Existenz von Normalspannungen in Fetten nachzuweisen, aber diese Messungen können nur mit geringer Genauigkeit durchgeführt werden. Es treten Bruch- und Scherabbauerscheinungen auf. Außerdem ist der Nullpunkt der Normalspannungsmessung um einen Betrag ungenau, welcher der Fließspannung proportional ist. Verfahren zur Verkleinerung dieser Ungenauigkeiten werden diskutiert.

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Presented at a joint meeting of the British Society of Rheology and the Italian Society of Rheology, Shrivenham, 8–11 th April 1975.

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With 11 figures     

The enantioselective synthesis of APTO and AETD: polyhydroxylated beta-amino acid constituents of the microsclerodermin cyclic peptides

The polyhydroxylated beta-amino acids (2S,3R,4S,5S,7E)-3-amino-8-phenyl-2,4,5-trihydroxyoct-7-enoic acid (APTO) and (2S,3R,4S,5S,7E,9E)-3-amino-10-(4-ethoxyphenyl)-2,4,5-trihydroxydeca-7,9-dienoic acid (AETD) are key components of the microsclerodermin family of anti-fungal cyclic peptides. They have been synthesised in protected form in twelve steps using a unified strategy, with the introduction of the unsaturated sidechain in the final step of the synthesis from a common aldehyde intermediate. The synthesis features the ordered application of asymmetric aminohydroxylation and dihydroxylation reactions to efficiently introduce the stereochemistry of the targets with high selectivity.     

Beam-foil lifetime data for 3s 3p 3 and 3s 2 3p 3d levels of Si-like Ni14+

In the EUV spectrum of foil-excited 24 MeV Ni ions the decays of the 3s 3p ³ and 3s ² 3p 3d levels to the 3s ² 3p ² levels of the ground configuration have been observed. For most of the levels decay curves have been obtained. The lifetime results compare well with predictions from semi-empirically scaled HXR calculations. Some problems with cascade repopulations will be discussed.     

Allylic selenosulfide rearrangement: a method for chemical ligation to cysteine and other thiols

Alkylation of potassium selenosulfate with allylic halides gives Se-allyl seleno Bunte salts. On reaction with thiols at room temperature, these afford mixed dialkyl selenosulfides, which undergo 2,3-sigmatropic rearrangement with loss of selenium, either spontaneously or with assistance by triphenylphosphine, thereby providing mixed dialkyl sulfides and a new permanent chemical ligation method. The process is illustrated through the lipidation of cysteine-containing tripeptides and by the allylation of 1-thioglucose tetraacetate.     

M(F)-dependent lifetimes due to hyperfine induced interference effects

We report on the first theoretical investigation of M(F)-dependent lifetimes due to interference between a magnetic octupole transition and a hyperfine induced electric quadrupole transition. Extensive multiconfiguration Dirac-Fock calculations are used to model the hyperfine quenching of the magnetic octupole decay of 3d(9)4s 3D3 and the state mixing between the 3D3 and 3D2 due to hyperfine interaction in nickel-like Xe26+.     

Photochromic long‐chain organomercury(II) dithizonate complexes in the azomethine series

The synthesis and characterization of a series­of 4 ‐ (4′‐ n ‐alkoxybenzylideneimino)phenyl‐­mercury<?tw=97.2%>(II) dithizonates, [C_nH_2n+1OC₆H₄CH­NC₆H₄Hg<?tw>(Hdptc)] (H₂dptc = 1,5‐diphenylthiocarbazone = dithizone; n = 1, 4, 12, 14 or 18), is described. The intermediate long‐chain organomercury(II) acetates were obtained by condensation of 4‐aminophenylmercury(II) acetate with the appropriate 4‐n‐alkoxybenzaldehydes. The thermal behaviour of the complexes was studied by polarized optical microscopy and differential scanning calorimetry but revealed no mesophases. All of the complexes, however, were reversibly photochromic (yellow ⇌ blue) upon irradiation of chloroform solutions with visible light, and the half‐lives of the metastable blue forms were substantially increased relative to that of the parent mercury(II) bis(dithizonate). The compounds were not photochromic in the solid state. Copyright © 2000 John Wiley & Sons, Ltd.     

Electron beam density imaging system at Beam study using a portable slit the Shanghai Electron Ion Trap

In this work, a portable slit imaging system is developed to study both the electron beam diameter and the profile of the newly developed Shanghai Electron Beam Ion Trap （Shanghai EBIT）. Images are detected by a charge coupled device （CCD） sensitive to both X rays and longer wavelength photons （up to visible）. Large scale ray tracings were conducted for correcting the image broadening effects caused by the finite slit width and the finite width of the CCD pixels. A numerical de-convolution method was developed to analyse and reconstruct the electron beam density distribution in the EBIT. As an example of the measured beam diameter and current density, the FWHM （full width at half maximum） diameter of the electron beam at 81 keV and 120 mA is found to be 76.2 μm and the density 2.00 × 10^3 A.cm-2, under a magnetic field of 3 T, including all corrections.     

Quenching of giant hysteresis effects in La(1-z)Y(z)Hx switchable mirrors

Hydrogen atoms adsorbed on TiO2(110)-(1x1) surfaces have been characterized by scanning tunneling microscopy (STM) combined with electron stimulated desorption (ESD) technique. Certain amounts of H atoms are unexpectedly found on the TiO2 surfaces annealed at 900 K. Two forms of adsorption were discriminated in STM images from the different sensitivity to ESD and tentatively assigned to hydroxyl-type (O-H) and hydride-type (Ti-H) species.