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排序方式: 共有43条查询结果,搜索用时 15 毫秒
1.
Ahmed Waqar Chowdhury Z. Z. Kazi S. N. Johan MR. Akram Naveed Oon C. S. Abdelrazek Ali H. 《Journal of Thermal Analysis and Calorimetry》2021,144(4):1517-1534
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers... 相似文献
2.
In quasi-steady operation, convection currents in a Bridgmandevice, used for producing a semi-conductor crystal, createinhomogeneities that may make the crystal unusable. It has oftenbeen suggested that additional forces due to rotation or magnetismmight be efficacious in reducing the segregation of the elementsof the alloy. It has been found that, over a wide range of rotationrates, there is no improvement in performance due to rotationabout the vertical axis. However, numerical results that havebeen obtained previously (Lee & Pearlstein, J. Crys. Growth240, 2002) indicate that, when effects of centrifugal buoyancyare introduced, a substantial reduction in segregation is achieved.In the work reported here, by contrast, in which we extend previouslarge-Rayleigh-number asymptotic analysis to include centrifugalbuoyancy, we find no improvement in radial segregation, butrather increasing segregation with increasing rotation rate. 相似文献
3.
S.D. Gopal Ram G. Ravi MR. Manikandan T. Mahalingam M. Anbu Kulandainathan 《Superlattices and Microstructures》2011,50(4):296-302
In the present work, a controlled growth of ZnO nanostructures by manipulating Zn metal ion concentration by the chelating action of ethylene diaminetetra acetic acid in hydrothermal method is studied. EDTA produces metal–chelate complex by the formation of bidentate ligand with Zn2+ in the solution and diminishes the reactivity of Zn metal cations. Concentration of EDTA in the mother solution was varied in different ranges like 3, 5 and 10 mM while retaining the zinc metal salt and the NaOH concentration the same. Three different morphologies of wurtzite structured ZnO nanostructures such as nanorods-bunch, separate/discrete uniformly sized hexagonal nanorods and tapered flower petals like shapes are achieved by 3, 5 and 10 mM strengths of EDTA, respectively. The medium concentration 5 mM of EDTA is found to have moderate control over producing ZnO nanostructures of uniform diameter and a high aspect (length to diameter) ratio. An array of vertically aligned free standing ZnO nanorods with uniform spacing is successfully achieved by the addition of 5 mM of EDTA in the mother solution and the same is studied for its fluorescence property at an excitation of 325 nm and it has exhibited a characteristic UV emission of ZnO around 383 nm. 相似文献
4.
5.
Headgroup effect on drag reduction and rheological properties of micellar solutions of quaternary ammonium surfactants 总被引:1,自引:0,他引:1
Two sets of cationic surfactants each with essentially the same alkyl chains but different headgroup structures were studied to investigate the effects of surfactant headgroup structure on micelle microstructures, drag reduction (DR) and rheological properties at certain counterion and surfactant concentrations. Cetyldimethylethylammonium bromide (CDMEAB) was compared with alkyltrimethyl ammonium bromide (CnTAB) and benzyldimethyl(hydrogenated tallow)ammonium chloride (DMHTB) was compared with alkyltrimethylammonium chloride (CmTAC), respectively. Surfactants with larger headgroups showed lower high temperature limits for DR. CDMEAB systems have better DR abilities than CnTAB below room temperature but the opposite is true at higher temperatures. DMHTB has stronger counterion binding ability than CmTAC, giving better DR properties than CmTAC at low counterion concentration, but has a lower upper temperature limit for DR. These results provide further understanding of the self-assembly nature of threadlike micelles of cationic surfactants and guidance for design of effective surfactant structures to meet particular DR requirements. 相似文献
6.
What is new in the field of neutrino detection? In addition to new projects probing both the low and high ends of the neutrino energy scale, an inexpensive, effective technique is being developed to allow tagging of antineutrinos in water Cherenkov (WC) detectors via the addition to water of a solute with a large neutron cross-section and energetic γ daughters. Gadolinium is an excellent candidate since in recent years it has become very inexpensive, now less than $8 per kilogram in the form of commercially available gadolinium trichloride. This non-toxic, non-reactive substance is highly soluble in water. Neutron capture on gadolinium yields an 8.0 MeV gamma cascade easily seen in detectors like Super-Kamiokande. The uses of GdCl3 as a possible upgrade for the Super-Kamiokande detector — with a view toward improving its performance as an antineutrino detector for supernova neutrinos and reactor neutrinos — are discussed, as are the ongoing R&;D efforts which aim to make this dream a reality within the next two years. 相似文献
7.
Turbulent Couette flow between two circular cylinders has been used for drag reduction experiments using surfactants. In the experiments presented here, only the outer cylinder rotates, the inner cylinder remains at rest and accurate measurements of the torque at the inner cylinder are measured. Water is used as a reference fluid. A drag reducing surfactant called Arquad S-50 (Akzo Nobel Surface Chemistry LLC, Chicago, Ill., USA) (5 mM)+NaSal (12.5 mM) was used as the drag reduction agent. This surfactant can reduce the drag up to 70% (a Reynolds number of about 70,000–150,000) as measured by pressure drop in a pipe flow. Experiments in Couette flow also show drag reduction in the turbulent range. Two arrangements were used, (1) one small trip-wire on the inner cylinder, and (2) four larger trip-wires on the outer cylinder. These trips reduce the critical Reynolds number for transition from laminar to turbulent flow. In case (1), we obtained 18% drag reduction at 5,000<Re<15,000 and in case (2), we obtained an average reduction of about 20% at 2,000<Re<10,000, increasing up to 30% at Re=15,000. The paper also discusses two important problems. First, the shear rate is not constant in the radial gap in circular Couette flow. For non-Newtonian fluids, where the molecular viscosity is a function of the shear rate, this effect must be considered. Second, which viscosity should be used in the Reynolds number? For pipe flow measurements, most authors use the viscosity of the solvent (generally water and Newtonian). For measurements in the Couette flow, we use a different approach, which is described in this paper. We conclude that Couette flow is a useful method for drag reduction investigations. Its advantage is the much smaller geometry in comparison to those of conventional test facilities such as wind tunnels, water, or oil channels or in tubes. 相似文献
8.
9.
J. L. Zakin R. Wu H. Luh K. G. Mayhan 《Journal of Polymer Science.Polymer Physics》1976,14(2):299-308
Data are presented to show that two correlations of viscosity–concentration data are useful representations for data over wide ranges of molecular weight and up to at least moderately high concentrations for both good and fair solvents. Low molecular weight polymer solutions (below the critical entanglement molecular weight Mc) generally have higher viscosities than predicted by the correlations. One correlation is ηsp/c[η] versus k′[η], where ηsp is specific viscosity, c is polymer concentration, [η] is intrinsic viscosity, and k′ is the Huggins constant. A standard curve for good solvent systems has been defined up to k′[η]c ≈? 3. It can also be used for fair solvents up to k′[η]c ≈? 1.25· low estimates are obtained at higher values. A simpler and more useful correlation is ηR versus c[η], where ηR is relative viscosity. Fair solvent viscosities can be predicted from the good solvent curve up to c[η] ≈? 3, above which estimates are low. Poor solvent data can also be correlated as ηR versus c[η] for molecular weights below 1 to 2 × 105. 相似文献
10.
An enclosed rotating disk apparatus (RDA) with rotational speed up to 5,500 rpm and with temperature control from −5 to 55°C
was designed to screen the turbulent drag reducing effectiveness of small samples of newly synthesized drag reducing additives.
First, the rotating disk was calibrated with water using both logarithmic and power law models. Then experiments were carried
out to measure the frictional torque reduction for a drag reducing aqueous cationic surfactant system (5 mM Ethoquad O12 with
12.5 mM sodium salicylate) over a range of Re. The maximum drag reduction at 30°C was about 47% at Re = 1.90 × 106. For the first time, results with the RDA were compared with those in a circular pipe flow system. They showed similar trends
indicating it is a useful screening device for small samples, giving conservative estimates of surfactant effectiveness compared
with pipe flow.
相似文献
Jacques L. ZakinEmail: |