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81.
The flow-field of a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers was numerically studied.Results obtained from four combustion models,combined with the re-normalization group(RNG) k-ε turbulence model,discrete ordinates radiation model and enhanced wall treatment are presented and discussed.The results are compared with a comprehensive database obtained from a series of experimental measurements.The flow patterns and the recirculation zone length in the combustion chamber are accurately predicted,and the mean axial velocities are in fairly good agreement with the experimental data,particularly at downstream sections for all four combustion models.The mean temperature profiles are captured fairly well by the eddy dissipation(EDS),probability density function(PDF),and laminar flamelet combustion models.However,the EDS-finite-rate combustion model fails to provide an acceptable temperature field.In general,the flamelet model illustrates little superiority over the PDF model,and to some extent the PDF model shows better performance than the EDS model. 相似文献
82.
The compression creep deformation of the high volume fraction of SiC particles reinforced Al-Mg-Si composite fabricated by pressure-less infiltration was investigated. The experimental results show that the creep stress exponents are very high at temperatures of 673 K, 723 K and 773 K, and if taking the threshold stress into account, the true stress exponent of minimum creep strain rate is still approximately 5, although the volume fraction of reinforcements is very high. The creep strain rate in the high volume fraction rein- forced aluminum alloy matrix composites is controlled by matrix lattice diffusion. It is found that the creep-strengthening effect of high volume fraction of silicon carbide particles is significant, although the particles do not form effective obstacles to dislocation motion. 相似文献
83.
通过对Co扩散阻挡层在CVD过程中冶金行为的理论分析,建立了计算Co扩散阻挡层临界厚度δ临的数学模型。指出:阻挡层厚度δ≥δ临是抑制Co对金刚石沉积不良影响的必要条件。 相似文献
84.
双合金热等静压复合工艺研究 总被引:5,自引:0,他引:5
主要探索采用双合金热等静压扩散连接工艺实现高温合金粉末和DD3单晶合金间可靠连接的可行性。研究内容包括热等静压(HIP)扩散连接温度及热处理对FGH95—DD3复合界面的成分扩散、界面组织以及叶片材料本身组织性能的影响。研究表明,通过合理的工艺选择与改进,可以在保证对偶材料性能满足要求的前提下实现界面的良好扩散与结合。 相似文献
85.
设计了压紧力装置,在普通空气炉中实现了转子及滑靴组件扩散焊连接;分别针对圆周面对接和端面对接两种结构的铜合金(ZCuSn10Pb2Ni3)和结构钢(30Cr3MoA)扩散焊工艺进行了研究,试验分析了压紧力、扩散焊温度及保温时间等参数对接头性能的影响,并得到了可获得牢固接头的扩散焊工艺参数。 相似文献
86.
Hemant L. Gohil Melanie J. Correll Thomas Sinclair 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
As part of a Bio-regenerative Life Support System (BLSS) for long-term space missions, plants will likely be grown at reduced pressure. This low pressure will minimize structural requirements for growth chambers on missions to the Moon or Mars. However, at reduced pressures the diffusivity of gases increases. This will affect the rates at which CO2 is assimilated and water is transpired through stomata. To understand quantitatively the possible effects of reduced pressure on plant growth, CO2 and H2O transport were calculated for atmospheres of various total pressures (101, 66, 33, 22, 11 kPa) and CO2 concentrations (0.04, 0.1 and 0.18 kPa). The diffusivity of a gas is inversely proportional to total pressure and shows dramatic increases at pressures below 33 kPa (1/3 atm). A mathematical relationship based on the principle of thermodynamics was applied to low pressure conditions and can be used for calculating the transpiration and photosynthesis of plants grown in hypobaria. At 33 kPa total pressure, the stomatal conductance increases by a factor of three with the boundary layer conductance increasing by a factor of ∼1.7, since the leaf conductance is a function of both stomatal and the boundary layer conductance, the overall conductance will increase resulting in significantly higher levels of transpiration as the pressure drops. The conductance of gases is also regulated by stomatal aperture in an inverse relationship. The higher CO2 concentration inside the leaf air space during low pressure treatments may result in higher CO2 assimilation and partial stomata closure, resulting in a decrease in transpiration rate. The results of this analysis offer guidelines for experiments in pressure and high CO2 environments to establish ideal conditions for minimizing transpiration and maximizing the plant biomass yield in BLSS. 相似文献
87.
本文介绍了高频输氧技术中气体输运机理的实验研究结果。用气管-支气管-肺模型来模拟人体呼吸系统,用热线和激光测速技术测量该模型内的气流。结果表明,整流效应和湍流扩散具有关键作用。 相似文献
88.
89.
The Ulysses spacecraft has been the first to orbit the Sun over its poles and to explore the heliosphere at these high heliolatitudes.
It has now completed two fast latitude scans, one at solar minimum and one at solar maximum. Since its launch in October 1990,
this mission has led to several surprising discoveries concerning energetic particles, cosmic rays, Jovian electrons, the
solar wind, the heliospheric magnetic field and the global features of the heliosphere. This review addresses mainly the propagation
and modulation of cosmic rays and other charged particles, from both an observational and theoretical point of view, with
emphasis on what has been learned from exploring the inner heliosphere to high heliolatitudes. This is done for solar minimum
and maximum conditions. The review is concluded with a summary of the main scientific discoveries and insights gained so far
from the Ulysses mission. 相似文献
90.