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141.
The turbulence characteristics of fully developed isothermal air flows through a symmetric trapezoidal duct were examined experimentally using Pitot tube and hot-wire anemometry over a Reynolds number range of 3.7–11.6×104. The measurements included local wall shear stress and the cross-sectional distributions of mean axial velocity, secondary velocities and Reynolds stresses. Four secondary flow cells were detected in a symmetric half of the duct. Although secondary velocity components were typically less than about 1% of the bulk axial velocity, their effect was especially pronounced on the distributions of turbulent kinetic energy and local wall shear stress.List of symbols
a, b, c, d
trapezoidal duct dimensions (Fig. 1)
-
A, B
coefficients in log law (Table 1)
-
D
h
equivalent hydraulic diameter
-
f
Darcy friction factor, (2D
h
/U
b
2
) (dP/dx)
-
k
turbulent kinetic energy per unit mass,
-
k
+
dimensionless turbulent kinetic energy, k/(
*)2
-
P
static pressure
-
Re
Reynolds number, U
b
D
h
/
-
s
distance along inclined wall, measured from top corner (Fig. 1)
-
u, v, w
fluctuating components of the velocities in the x, y, z directions
-
u
+, v
+, w
+
dimensionless turbulence intensities; u
2/
*, v
2/
*, w
2/
*
-
u
*
local friction velocity, (
w
/)1/2
-
*
average friction velocity, (¯gt/)1/2
-
axial mean velocity (time-average)
-
U
b
average mean axial velocity
-
U
sec
resultant of ¯V and ¯W, (¯V
2+¯
2)1/2
-
U
+
dimensionless velocity, /u
*
-
¯V, ¯W
mean velocities in the y, z directions (secondary velocities)
-
x
axial direction
-
y, 2
horizontal and vertical directions (Fig. 1)
-
z
+
dimensionless distance from (and normal to) a wall, zu
*/v
-
distance from wall (at y=0) to location of maximum axial velocity
-
laminar dynamic viscosity
-
v
kinematic viscosity
-
air density
-
w
local wall shear stress
-
¯
w
average of local wall shear stresses over all walls
-
¯
average wall shear stress, (dP/dx) (D
h
/4)
-
corner angle of trapezoidal duct (Fig. 1)
A version of this paper was presented at the 10th Symposium on Turbulence, University of Missouri-Rolla, Sept. 22–24, 1986 相似文献
142.
A number of new hydrazones bearing pyridine-2,6-bis-carboxamides were synthesized and elucidated by spectral and elemental analysis. 2,6-Bis-carboxamide pyridine hydrazide was treated with various active carbonyl compounds containing formyl or methanoyl groups to give hydrazones and Schiff bases. 相似文献
143.
N. M. Khalifa E. S. Nossier M. A. Al-Omar A. E. Amr 《Russian Journal of General Chemistry》2016,86(4):919-923
3-Aryl-5-[(Z)-pyrenylmethylene]-2-alkylthiohydantoins and 3-Aryl-5-[(Z)-pyrenylmethylene]-2-(D-glycosyl)-2-thiohydantoins functionalized with different aromatic and glycoside substituents have been synthesized by the reaction of (Z)-3-(4-methoxyphenyl)-5-[(pyren-8-yl)methylene]-2-thiohydantoin with alkyl halides, cyclic and acyclic nucleosides via various routes with moderate to good yields and characterized by 1H, 13C NMR and mass spectra and elemental analysis 相似文献
144.
Reaction of 4-substituted quinoline hydrazide with some aldohexoses and aldopentoses gave a series of new N-β-glycosides. The following cyclization of N-β-glycosides with acetic anhydride led to O-acetyl-[5-(2-phenylquinolin-4-yl)-1,3,4-oxadiazol-2-yl]-D-glycosides. Structure of the newly synthesized products was elucidated by chemical and spectroscopic methods. 相似文献
145.
Ibrahim A Khalifa SI Khafagi I Youssef DT Khan S Mesbah M Khan I 《Chemical & pharmaceutical bulletin》2008,56(9):1253-1258
Ursolic acid (1) and kaempferol (3) are two major constituents of the Mediterranean plant Nerium oleander L. Microbial metabolism of (1) with Aspergillus flavus (ATCC 9170) resulted in the formation of 3-oxo-ursolic acid derivative, ursonic acid (2). On the other hand, Cunninghamella blakesleeana (ATCC 8688A) was able to convert (3) into kaempferol 3-O-beta-D-glucopyranoside (4) as well as the new natural product kaempferol 4'-sulfate (5). Incubation of kaempferol with Mucor ramannianus (ATCC 9628) led to the isolation of one metabolite identified as kaempferol 4'-O-alpha-L-rhamnopyranoside (6). Transformation of kaempferol to the new compound kaempferol 7-O-beta-D-4-O-methylglucopyranoside (7) and herbacetin 8-O-beta-D-glucopyranoside (8) was observed after fermentation with Beauveria bassiana (ATCC 13144). Cytotoxic as well as antioxidant activities of the isolated metabolites were determined. 相似文献
146.
The molybdenum clectiode is found to act as a suitable means for the determination of the hydrogen ion concent-ration. Polished electrodes in aerated solutions give potentials which do not vary appreciably with time. The potential measured in solutions of different H+-ion activity is a function of pH from 2–11. pKa values determined from neutralization curves of some acids are not much different from those obtained by other authors, using different methods. Polished or aged electrodes in aerated or oxygen-free solutions could be used satisfactorily for determining tlie end-points in neutralization reactions. 相似文献
147.
148.
A modified method is reported for the conversion of unsaturated sulfonamides into their cyclic saturated counterparts. This method utilises a single palladium catalyst for an intramolecular Heck reaction and subsequent transfer hydrogenation, which is achieved in one-pot following the addition of ammonium formate. Accordingly, a range of fourteen structural variations are reported and under optimal conditions the adducts were generated in typically good to excellent yields. Notably, discrimination of differentially substituted dienes can be accomplished in the case of compounds 28 and 29 and the process was only observed to fail with the more sterically hindered precursor 32. 相似文献
149.
Copper(II) forms 1:1 and 1:2 intense red complexes with phenanthraquinone monophenylthiosemicarbazone (PPT) at pH 3-3.5 and > or =6.5, respectively. These complexes exhibit maximal absorbance at 545 and 517 nm, the molar absorptivity being 2.3 x 10(4) and 4.8 x 10(4) l mol(-1) cm(-1), respectively. However, the 1:1 complex was quantitatively floated with oleic acid (HOL) surfactant in the pH range 4.5-5.5, providing a highly selective and sensitive procedure for the spectrophotometric determination of CuII. The molar absorptivity of the floated Cu-PPT complex was 1.5 x 10(5) l mol)(-1) cm(-1). Beer's law was obeyed over the range 3-400 ppb at 545 nm. The analytical parameters affecting the flotation process and hence the determination of copper traces were reported. Also, the structure of the isolated solid complex and the mechanism of flotation were suggested. Moreover, the procedure was successfully applied to the analysis of CuII in natural waters, serum blood and some drug samples. 相似文献
150.
M. M. Abdel-Badci H. M. Aly S. M. Khalifa H. F. Aly 《Isotopes in environmental and health studies》2013,49(9):378-380
The extraction of uranium as well as Eu-(152 + 154), Co-60, Ru-103 and Cs-137 by di(2-ethylhexyl) phosphoric acid (HDEHP), tricaprylmethyl ammonium chloride (Aliquate-336) and tricapryltertiaryamine (Alamine-336) in kerosene from aqueous nitrate medium of constant ionic strength, 0.6 (H+, NaNO3) was investigated. The aqueous phase used is a representative medium for certain medium level waste (MLW) solutions. The obtained results indicate that HDEHP system is more suitable for the separation of U(VI) and Eu(III) from Ru(III), Co(II) and Cs(I). Using HDEHP loaded on XAD-4, chromatographic extraction was applied successfully for the recovery of uranium and Eu(152+154) from the aforementioned solution. Die Extraktion von Uranium wie auch von Eu-(152 + 154), Co-60, Ru-103 und Cs-137 durch Di(2-ethylhexyl) phosphorsäurc (HDEHP), Tricaprylmethylammoniumchlorid (Aliquate-336) und Tricapryl tertiäramin (Alamin-336) in Kerosin aus wäβrigen Nitratlösungen bei einer konstanten Ionenstärke von 0,6 (H+, NaNO3) wurde untersucht. Die verwendete wäβrige Phase ist für eine mittelaktive Abfallösung (MLW) repräsentativ. Die Ergebnisse zeigen, daβ das HDEHP-System geeigneter zur Abtrennung des U(VI) und des Eu(III) vom Ru(III), Co(II) und Cs(I) ist. Bei Verwendung eines HDEHP-beladenen Austauschers (XAD-4) konnte eine chromatographische Extraktion zur Rückgewinnung des Uraniums und des Eu-(152 + 154) von der oben erwähnten Lösung erfolgreich angewendet werden. 相似文献