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991.
992.
Sergey V. Polyakov 《Journal of Modern Optics》2013,60(9):1045-1052
We review radiometric techniques that take advantage of photon counting and stem from the quantum laws of nature. We present a brief history of metrological experiments and review the current state of experimental quantum radiometry. 相似文献
993.
Horizontal axis wind turbines can experience significant time varying aerodynamic loads that has the potential to cause adverse effects on structural, mechanical, and power production. The progress in the wind industry has caused the construction of wind farms in areas prone to high seismic activity. With the advances in computational tools, a more realistic representation of the behavior of wind turbines should be performed. One of the simulation platforms was developed using the 5 MW NREL utility scale reference turbine model. The performed simulations will be used to evaluate the effects of aerodynamic and seismic load coupling on the power generation and structural dynamics behavior of this structure. Different turbine operational scenarios such as (i) normal operational condition with no earthquake, (ii) idling condition with the presence of seismic loads, (iii) normal operational condition with earthquake, and (iv) earthquake-induced emergency shutdown will be simulated with various loading conditions to show the differences in generated power and dynamic response. The results of this paper provide formulations for calculating generated power and design deriving parameters by considering different intensity measures. Moreover, the effects of aerodynamic damping and pitch control system are presented to shows reduction in the resulting design demand loads. 相似文献
994.
AbstractA nickel-based single-crystal superalloy was employed to investigate the preferred growth orientation behavior of the (γ + γ′) eutectic and the effect of these orientations on the segregation behavior. A novel solidification model for the eutectic island was proposed. At the beginning of the eutectic island’s crystallization, the core directly formed from the liquid by the eutectic reaction, and then preferably grew along [100] direction. The crystallization of the eutectic along [110] always lagged behind that in [100] direction. The eutectic growth in [100] direction terminated on impinging the edge of the dendrites or another eutectic island. The end of the eutectic island’s solidification terminates due to the encroachment of the eutectic liquid/solid interface at the dendrites or another eutectic island in [110] direction. The distribution of the alloying elements depended on the crystalline axis. The degree of the alloying elements’ segregation was lower along [100] than [110] direction with increasing distance from the eutectic island’s center. 相似文献
995.
Daniel Leidermark David AspenbergDavid Gustafsson Johan Moverare Kjell Simonsson 《Computational Materials Science》2012,51(1):273-280
Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g. gas turbine components, where great care must be given with respect to high temperature fatigue. Due to the large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As a consequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigate this variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens, where placements and orientations of the grains were randomised. Furthermore, each grain was modelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion in fatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-base superalloys may show a considerable variation, which cannot be captured by one single deterministic analysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitude that it needs to be taken into account in industrial applications where highly stressed coarse grained materials are used. 相似文献
996.
Effective cooling is critical for safe and efficient operation of proton exchange membrane fuel cell (PEMFC) stacks with high power. The narrow range of operating temperature and the small temperature differences between the stack and the ambient introduce significant challenges in the design of a cooling system. To promote the development of effective cooling strategies, cooling techniques reported in technical research publications and patents are reviewed in this paper. Firstly, the characteristics of the heat generation and cooling requirements in a PEMFC stack are introduced. Then the advantages, challenges and progress of various cooling techniques, including (i) cooling with heat spreaders (using high thermal conductivity materials or heat pipes), (ii) cooling with separate air flow, (iii) cooling with liquid (water or antifreeze coolant), and (iv) cooling with phase change (evaporative cooling and cooling through boiling), are systematically reviewed. Finally, further research needs in this area are identified. 相似文献
997.
Combined generation and separation of hydrogen in an electrochemical water gas shift reactor (EWGSR)
Hydrogen rich gas, originating from fossil fuel reforming processes or biomass gasification, contains a significant amount of CO. Typically, the yield of H2 is increased with subsequent water gas shift units, converting CO to CO2 and additional H2. This study describes a new reactor concept enabling the water gas shift reaction and the separation of the generated hydrogen in one process step by using electrical energy. This electrochemical water gas shift reactor applies a H3PO4-doped Poly(2,5-benzimidazole) membrane as electrolyte and carbon supported Pt or PtRu as anode catalyst. The reactor operation was investigated at 130 °C and 150 °C with a H2 free anode feed stream of humidified CO and N2. The experimental results show the feasibility of the reactor concept, as H2 was generated at the cathode according to Faradays Law. Anodic PtRu led to lower power demands than Pt. The operation at the two temperatures showed that 130 °C results in a lower electrical power demand while generating an equal amount of H2. The feasibility of the reactor was assessed using exergy efficiency analysis. 相似文献
998.
Single‐walled carbon nanotubes (SWCNTs) dispersed in N‐methylpyrrolidone (NMP) were functionalized by addition of polystyryl radicals from 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐ended polystyrene (SWCNT‐g‐PS). The amount of polystyrene grafted to the nanotubes was in the range 20‐25 wt% irrespective of polystyrene number‐average molecular weight ranging from 2270 to 49 500 g mol?1. In Raman spectra the ratios of D‐band to G‐band intensity were similar for all of the polystyrene‐grafted samples and for the starting SWCNTs. Numerous near‐infrared electronic transitions of the SWCNTs were retained after polymer grafting. Transmission electron microscopy images showed bundles of SWCNT‐g‐PS of various diameters with some of the polystyrene clumped on the bundle surfaces. Composites of SWCNT‐g‐PS in a commercial‐grade polystyrene were prepared by precipitation of mixtures of the components from NMP into water, i.e. the coagulation method of preparation. Electrical conductivities of the composites were about 10?15 S cm?1 and showed no percolation threshold with increasing SWCNT content. The glass transition temperature (Tg) of the composites increased at low filler loadings and remained constant with further nanotube addition irrespective of the length and number of grafted polystyrene chains. The change of heat capacity (ΔCp) at Tg decreased with increasing amount of SWCNT‐g‐PS of 2850 g mol?1, but ΔCp changed very little with the amount of SWCNT‐g‐PS of higher molecular weight. The expected monotonic decrease in ΔCp coupled with the plateau behavior of Tg suggests there is a limit to the amount that Tg of the matrix polymer can increase with increasing amount of nanotube filler. Copyright © 2012 Society of Chemical Industry 相似文献
999.
《分离科学与技术》2012,47(3):564-574
ABSTRACTThe exploitation efficiency of natural gas hydrate is highly affected by sand production. In this paper, hydrocyclone purification separator was designed. A combination of single factor with computational fluid dynamics (CFD) was used to optimize the structure parameters. The performance of optimized hydrocyclone was also investigated. It shows that the sand separation efficiency increases from 90.4% to 98.7%, and the natural gas hydrate separation efficiency increases from 89.5% to 97.8%. Furthermore, the cut size of sand and natural gas hydrate are as low as 3 and 2 µm, respectively, and separation efficiency remains above 80% under inlet parameters. It can provide some reference for the design and manufacture of the in situ purification separator for gas hydrate mixture slurry. 相似文献
1000.
Hongbin Gu Jiangning Wu Philip Chan Ginette Turcotte Tianjiang Ye 《Chemical Engineering Research and Design》2012
To improve surface hydrophilicity and to reduce fouling, commercial polypropylene microfiltration membranes were ozonated to generate peroxides as grafting sites for hydrophilic monomers. Ozonation was conducted in aqueous and gaseous phases, respectively. In both phases, the amount of peroxides increased with the ozonation time. A novel way to enhance the generation of peroxides was tested, i.e., adding homogeneous catalyst, CuSO4, to aqueous ozonation. Results showed that with an optimum dose of 0.05 g/L of CuSO4, the peroxides generated were 18.2% more than that by the non-catalyzed ozonation in aqueous phase. It was also confirmed by scavenger tests that during the aqueous ozonation both molecular ozone and free radicals contributed to the oxidation of the membranes, the latter was formed from the self-decomposition of ozone in water. Graft polymerization was also conducted after the generation of peroxides. A hydrophilic monomer, acrylic amide, was graft polymerized onto the membrane surface. The successful grafting of acrylic amide was confirmed by the formation of new peaks corresponding to amide groups in FTIR spectra. Results of contact angle measurements and filtration tests indicated that aqueous ozonation was more effective than its gaseous counterpart in terms of hydrophilicity improvement. In addition, the XRD analysis revealed that the ratio of the membrane surface crystallinity to amorphousity was changed by both ozonation and graft polymerization. Results of SEM scanning also showed changes in membrane surfaces after modification. 相似文献