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  • 1
    Publication Date: 2015-01-16
    Description: The current development of modern pumped storage plants aims towards a higher flexibility in operation, an extended operation range of the hydraulic machine (especially in the pumping mode), and a higher reliability. The pumping requirements are the crucial design drivers, since, even if the turbine mode performance is very sound, the success of a project depends also on the pump turbine delivering the required maximum pump head and starting reliably in pump mode. Pump hump (pump instability working points at highest head) which is an instability source to the pump-turbine vibration is a serious damage to the pump operation on high head. So the pump hump and cavitation number based on the numerical simulation and experiment results are shown in this paper. The pump hump is sensitive affected by the cavitation number. With the cavitation number decreasing, the hump on flow characteristic curve (e.g. head-flow rate curve, H-Q curve) is gradually decreasing until vanished. P...
    Print ISSN: 1757-8981
    Electronic ISSN: 1757-899X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
    Publication Date: 2017-02-14
    Description: In order to investigate the wettability of multicrystalline silicon (mc-Si) with the etching solutions during metal-assisted chemical etching process, different surface structures were fabricated on the p-type multi-wire slurry sawn mc-Si wafers, such as as-cut wafers, polished wafers, and wafers etched in different solutions. The contact angles of different etching solutions on the surfaces of the wafers were measured. It was noted that all contact angles of etching solutions were smaller than the corresponding ones of deionized water, but the contact angles of different etching solutions were quite different. Among the contact angles of the etching solutions of AgNO 3 -HF, H 2 O 2 -HF, TMAH and HNO 3 -HF, the contact angle of TMAH solution was much larger than the others and that of HNO 3 -HF solution was much smaller. It is suggested that the larger contact angle may lead to an unevenly etching of silicon wafer due to the long rete...
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
    Publication Date: 2015-08-11
    Description: Different capacity control methods are used for adjusting suction flow of reciprocating compressors to meet process need. Compared with recycle or bypass and suction throttling, three capacity control methods of speed control, clearance pockets and suction valve unloading are preferred due to their energy-saving at operating condition of partial load. The paper reviewed state of the art of the current capacity control technologies and their principles. A comprehensive mathematical model was developed to predict thermodynamic and dynamic performance of reciprocating compressors equipped with the capacity control systems of four above-mentioned methods. Comparison of shaft work and mechanical efficiency were conducted for different capacity control methods at the same condition. In addition, their influence on p-v diagram and valve motion were also studied, which is important for reliability and life of the reciprocating compressors. These results were helpful for selection of the ...
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 4
    Publication Date: 2012-07-04
    Description: A cellular automaton model has been developed to simulate the austenitization process of ASTM A216 WCA cast steel during heating process. The dissolution of pearlite and the transformation of ferrite into austenite were simulated. The calculation domain was divided into square cells, which are characterized by certain attributes that represent the status of each cell: pearlite (P), ferrite (α), austenite (γ) or γ /α interface. The dissolution of pearlite was described by nucleation and growth of austenite. A mixed-mode model in multicomponent system was employed to calculate the growth velocity of the γ /α interface. According to Burke and Turnbull's theory, austenite grain coarsening induced by γ /γ grain boundary migration was simulated. To validate the model, dilatometric and quenching experiments were carried out. The dilatometric experiment was conducted using a Gleeble1500D with a sample 8 mm in diameter. The temperature of the sample was measured using thermocouples welde...
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
    Publication Date: 2014-12-11
    Description: As an important component of the blade-control system in Kaplan turbines, piston rods are subjected to fluctuating forces transferred by the turbines blades from hydraulic pressure oscillations. Damage due to unsteady hydraulic loads might generate unexpected down time and high repair cost. In one running hydropower plant, the fracture failure of the piston rod was found twice at the same location. With the transient dynamic analysis, the retainer ring structure of the piston rod existed a relative high stress concentration. This predicted position of the stress concentration agreed well with the actual fracture position in the plant. However, the local strain approach was not able to explain why this position broke frequently. Since traditional structural fatigue analyses use a local stress strain approach to assess structural integrity, do not consider the effect of flaws which can significantly degrade structural life. Using linear elastic fracture mechanism (LEFM) approaches...
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
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  • 6
    Publication Date: 2018-07-31
    Description: The vibration and noise of large Francis-turbine units tends to increase, the efficiency decreases and the units operate unstably if the units operate under the cavitation condition. Hence it must be eradicated completely that the units run under the cavitation condition. Nowadays, the judgment of inception cavitation of model Francis-turbine runner blades remains stagnant at the stage of artificial observation so that the results lacks of objectivity and consistency. An auto-test method based on acoustics theory and the principle of cavitation is presented. When cavitation happens, the acoustic energy radiated by bubbles while collapsing is different at different stages of cavitation, for the size and number of bubbles are different. And therefore the distribution of cavitation noise energy in the frequency domain varies along with the severe degree of cavitation, according to which the inception cavitation can be determined exactly by acquiring the acoustics signals in the wat...
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  • 7
    Publication Date: 2018-07-31
    Description: The unsteady cavitating flows around a NACA66 hydrofoil with chord length 150 mm and the attack angle of 6 degrees was numerically simulated using two different turbulence models: the standard k-ε turbulence model and the PANS model. The results show that the standard k-ε turbulence model over predicts the eddy viscosity in the rear part of the cavity and fails to predict the unsteady shedding dynamics. However, it is found that the PANS model can accurately capture the general features of unsteady cavitating flow and the predicted shedding frequency agrees fairly well with the corresponding experimental data. Based on the predicted numerical results, the vorticity transport equation was implied to further analyze the strong interaction between the cavitation and vortex. The foundings in this study can provide further insight into the mechanism of cavitation shedding dynamics.
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  • 8
    Publication Date: 2018-08-04
    Description: Lead is a heavy metal with neurotoxicity, and excessive lead in water can lead to the deterioration of water quality and accumulate in aquatic organisms. Thus, it is necessary to explore quick and effective methods for the determination of Pb 2+ in water environment. In pH=5.5 weak acidic solution, it is found that Pb 2+ can combine with XO to form a red complex PbXO, which has a strong resonance light scattering strength at the wavelength of 342 nm under the sensitization effect of the cetyl trimethyl ammonium bromide(CTMAB). The resonance light scattering strength has good linear relationship with the concentration of Pb 2+ in the range of 0.01 mg L −1 ∼0.1 mg L −1 . Therefore, a convenient strategy has successfully realized the lead detection with the detection limits of 1.05×10 −2 mg L −1 and the relative standard deviation of 1.89 % at a concentration 0.02 mg L −1 . The recovery is in the range of ...
    Print ISSN: 1757-8981
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 9
    Publication Date: 2018-10-12
    Description: Surface coarse structure is one of key factors affecting the superhydrophobicity, yet it’s not very clear that what kind of structure is the best for hydrophobicity. Herein in order to study the effect of surface coarse structure, eight kinds of spherical SiO 2 (20 nm, 60 nm, 200 nm, 500 nm, 1 μm, 2 μm, 5 μm and 10 μm) were taken as raw material respectively to explore the effect of particle size on the hydrophobic performance. SiO 2 was deposited on the glass substrate layer by layer using the electrostatic assembly method based on the reaction of amino and epoxy groups. The sample’s structure and properties were characterized respectively by scanning electron microscopy and contact angle measuring instrument. The relationship between SiO 2 particle size and surface hydrophobicity was explored and the superhydrophobic stability were tested. The results show that the surface of SiO 2 film layers are stacked together and arranged tightly, a...
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  • 10
    Publication Date: 2018-11-06
    Description: Efficient simultaneous nitrogen removal and phosphorus accumulation microorganisms are great significance for the purification treatment of high salt wastewaters containing N and P. In this paper, the processes of nitrogen removal and phosphorus accumulation of Halomonas sp. H12 strain under high salt conditions were investigated. The optimal conditions of nitrogen removal and phosphorus accumulation were examined separately by using response surface methodology. The results showed that the Halomonas sp. H12 strain had high efficiency competent of nitrogen removal and phosphorus accumulation under high salt conditions under both growth stage and non-growth stage. Within 108 h, the rates of the nitrogen removal and phosphorus accumulation reached 78.51% and 49.18% respectively. During 0-84 h, the strain was in the growth stage, and its nitrogen removal rate and phosphorus accumulating rate increased gradually. At 84-108 h, the strain then entered the non-growth stag...
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