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981.
AnalyticalStudyonImpingementHeatTransferwithSingle-PhaseFree-SurfaceCircularLiquidJetsAnalyticalStudyonImpingementHeatTransfe... 相似文献
982.
The sickle bush (Dichrostachys cinerea (L.) Wight & Arn.) comprises a woody legume shrub which is widely distributed throughout of the tropical areas of Africa, Asia and Oceania, being found as well in Cuba where it represents a difficult to control invasive plant. It holds great silvopasture and energy crop potentials. In southwestern Spain a two year field trial was conducted contemplating also another six hardwood taxa commonly used as energy crops. The sickle bush above ground dry biomass fraction was 60.4%; sickle bush displayed a high transpiration rate during hot days (3.02 kg m−2 d−1 to 6.82 kg m−2 d−1); cold winter temperatures (<−2 °C) together with hot and dry summer air (<20% relative humidity) committed survival and growth. The physical-chemical wood properties and the pellets thereof derived were analyzed and compared to those of the other energy crop taxa. The within other woody species normal chemical composition range coupled to a high wood density and energetic use properties (19.2 MJ kg−1 higher heating value, 29 g kg−1 ash content) all allow for an industrial use. Pellets evidenced also good physical and mechanical properties (690 kg m−3 bulk density, 42 g kg−1 moisture content). However, the mechanical durability (93.9%) was slightly less than that required by the non-industrial use standards, therefore further improvements should be studied. All of the above could encourage scrubland cuts in Cuba as a mechanical control method, in addition to the expansion of plantations within of their tropical climate based natural habitats. 相似文献
983.
984.
研究了旬阳钟家坪水电站溢流坝的面流消能问题,通过分析确定了合理的溢流坝跌坎高度、鼻坎挑角和反弧半径等参数,并对下游水面线、水面波动和流速分布等情况进行了试验研究,为面流消能设计提供了依据,保证了设计的可靠性。 相似文献
985.
Simultaneous point measurements of temperature, mixture fraction, major species, and OH concentrations in a lifted turbulent hydrogen jet flame are reprocessed to obtain the Favre average and conditional mean profiles. Large discrepancies between the Favre average and the ensemble average temperature, H2O, and OH mole fractions are found at the lifted flame base, due to density weighting of fairly large samples of unreacted mixtures. Conditional statistics are used to reveal the reaction zone structure in mixture fraction coordinates. The cross-stream dependence of conditional reactive scalars, which is most notable at the lifted flame base and decreases to negligible levels with increasing streamwise positions, could be attributed to radial differences in both the Damköhler number and the level of partial premixing. Conditional results indicate that the lifted flame is stabilized at the outer region of the jet characterized by low strain rates and lean mixtures. Comparison of the measured conditional mean OH vs H2O with a series of stretched laminar partially premixed flame and diffusion flame calculations reveals that strong partial premixing takes place at the lifted flame base and the strain rates vary from a=14,000 to 100 s−1. The level of partial premixing and the strain rate decrease with increasing downstream locations. The range of estimated scalar dissipation rates (χ≈1–0.13 s−1) at a further downstream location (x/D=33.3) is in agreement with reported values and the flame composition reaches an equilibrium condition at x/D=194.4. These results combined with previously reported data provide a benchmark data set for evaluation and refinement of turbulent combustion models for lifted hydrogen jet flame predictions. 相似文献
986.
R.W. Schefer W.G. Houf T.C. Williams B. Bourne J. Colton 《International Journal of Hydrogen Energy》2007
Measurements were performed to characterize the dimensional and radiative properties of large-scale, vertical hydrogen-jet flames. This data is relevant to the safety scenario of a sudden leak in a high-pressure hydrogen containment vessel and will provide a technological basis for determining hazardous length scales associated with unintended hydrogen releases at storage and distribution centers. Jet flames originating from high-pressure sources up to 413 bar (6000 psi) were studied to verify the application of correlations and scaling laws based on lower-pressure subsonic and choked-flow jet flames. These higher pressures are expected to be typical of the pressure ranges in future hydrogen storage vessels. At these pressures the flows exiting the jet nozzle are categorized as underexpanded jets in which the flow is choked at the jet exit. Additionally, the gas behavior departs from that of an ideal-gas and alternate formulations for non-ideal gas must be introduced. Visible flame emission was recorded on video to evaluate flame length and structure. Radiometer measurements allowed determination of the radiant heat flux characteristics. The flame length results show that lower-pressure engineering correlations, based on the Froude number and a non-dimensional flame length, also apply to releases up to 413 bar (6000 psi). Similarly, radiative heat flux characteristics of these high-pressure jet flames obey scaling laws developed for low-pressure, smaller-scale flames and a wide variety of fuels. The results verify that such correlations can be used to a priori predict dimensional characteristics and radiative heat flux from a wide variety of hydrogen-jet flames resulting from accidental releases. 相似文献
987.
D. Demare 《Combustion and Flame》2004,139(4):312-328
Lifted nonpremixed jet flames are often used in industrial processes and present inherent difficulties such as their reattachment to the burner, blowout, and poor combustion. One solution is to control the jet by acoustic forcing. For flames lifted in the hysteresis zone where anchoring may occur, forcing at high amplitudes and middle frequencies (around 200 Hz) changes the combustion regime and prevents reattachement. The common long yellow plume, due to soot radiation, vanishes. The flame becomes shorter, totally blue and stabilizes at a higher position above the burner. The phenomenon is explained using the results obtained by analyzing the flow dynamics with high-speed laser tomography, laser Doppler anemometry, particle image velocimetry, and Mie scattering techniques. Measurements show that the excitation periodically generates axial velocities higher than the maximum velocity of the hysteresis zone, leading to flame liftoff. Some primary and streamwise eddy vortices similar to natural instabilities develop during the jet deceleration. Contrary to the unexcited case, these structures, disorganized by the superimposition of the forcing wave, lead to quasi-homogeneous turbulence which provides efficient mixing and improves the combustion regime. Finally, the frequency is sufficiently high to avoid excessive fluctuations of the lift-off height and the reattachment to the burner. 相似文献
988.
989.
A novel wet vapor photoresist stripping technology is developed as an alternative to dry plasma ashing and wet stripping.Experiments using this technology to strip hard baked SU-8 photoresist,aurum and chromium film are carried out.Then the images of stripping results are shown and the mechanism is analyzed and discussed. The most striking result of this experiment is that the spraying mixture of steam and water droplets can strip photoresist and even metal film with ease. 相似文献
990.
Based on current voltage (I-Vg) and capacitance voltage (C-Vg) measurements, a reliable procedure is proposed to determine the effective surface potential Vd.Vg/ in Schottky diodes. In the framework of thermionic emission, our analysis includes both the effect of the series resistance and the ideality factor, even voltage dependent. This technique is applied to n-type indium phosphide (n-InP) Schottky diodes with and without an interfacial layer and allows us to provide an interpretation of the observed peak on the C-Vg measurements. The study clearly shows that the depletion width and the flat band barrier height deduced from C-Vg, which are important parameters directly related to the surface potential in the semiconductor, should be estimated within our approach to obtain more reliable information. 相似文献