The combined effects of the magnetic field, permeable walls, Darcy velocity, and slip parameter on the steady flow of a fluid in a channel of uniform width are studied. The fluid flowing in the channel is assumed to b...The combined effects of the magnetic field, permeable walls, Darcy velocity, and slip parameter on the steady flow of a fluid in a channel of uniform width are studied. The fluid flowing in the channel is assumed to be homogeneous, incompressible, and Newtonian. Analytical solutions are constructed for the governing equations using Beavers-Joseph slip boundary conditions. Effects of the magnetic field, permeability, Darcy velocity, and slip parameter on the axial velocity, slip velocity, and shear stress are discussed in detail. It is shown that the Hartmann number, Darcy velocity, porous parameter, and slip parameter play a vital role in altering the flow and in turn the shear stress.展开更多
为提高防冲支架能量吸收性能以应对煤炭资源深部开采趋势下的冲击地压频发问题,提出了一种具有圆形与多边形混合截面的多胞薄壁吸能构件应用于防冲支架立柱。基于简化超折叠单元(Simplified Super Folding Element,SSFE)理论剖析了不同...为提高防冲支架能量吸收性能以应对煤炭资源深部开采趋势下的冲击地压频发问题,提出了一种具有圆形与多边形混合截面的多胞薄壁吸能构件应用于防冲支架立柱。基于简化超折叠单元(Simplified Super Folding Element,SSFE)理论剖析了不同截面形状和肋板布局的多胞薄壁吸能构件能量耗散途径,构建了轴向压溃条件下吸能构件的能量吸收平衡方程,并推导出了等厚度和非等厚度2种吸能构件平均支反力预测公式;通过轴向压溃仿真获得了各类型多胞薄壁吸能构件吸能量曲线、支反力曲线以及屈曲变形形态,发现圆形与八边形混合截面、边延伸肋板布局的多胞薄壁吸能构件(P8-2类型)具备相对吸能优势,深入考察了内嵌管截面尺寸、薄壁管壁厚和肋板厚度对其吸能效果的影响规律,即:3种结构参数对弯曲褶皱形态和塑性铰数量影响显著,对吸能特性参数有着不同且非简单单向变化的影响趋势,同时验证了基于SSFE理论的平均支反力理论模型具有较高预测精度;依托均匀试验数据,拟合出了吸能特性参数关于构件结构参数的回归方程,并利用NSGA-II遗传算法进行优化求解,最终确定多胞薄壁吸能构件内嵌管截面尺寸为122 mm,薄壁管壁厚度为2.6 mm,肋板厚度为2.7 mm;进一步通过轴向压溃仿真验证与对比分析,结果表明:经结构参数优化后的多胞薄壁吸能构件具备更好的能量吸收效果且支反力波动较小,可使让位防冲过程更加可靠,能够为防冲吸能构件设计提供有益参考。展开更多
Statistical analysis of the entrance and wall dynamics of a high-flux gas-solid riser was done using solid concentration time series data collected from a 76 mm internal diameter and 10 m high riser of a CFB system wi...Statistical analysis of the entrance and wall dynamics of a high-flux gas-solid riser was done using solid concentration time series data collected from a 76 mm internal diameter and 10 m high riser of a CFB system with a twin-riser operated at 4.0 to 10.0 m/s gas velocity and 50 to 550 kg/m2s solids flux. Spent fluid catalytic cracking catalyst particles with 67 μm mean diameter and density of 1500 kg/m3 together with 70% to 80% humid air was used. Solid concentration data were analysed using code prepared using FORTRAN 2008 to get statistical parameters and plot their profiles. Results obtained show that the gas-solid suspension flow in the riser is dominated by low solid concentration in the centre region and high solid concentration in the wall region which forms a core-annulus flow structure. The mean solid concentration in the wall region decreases with riser height from the dense bottom section to less dense in the fully developed flow section at the top of the riser. The gas-solid suspension flow in the centre region is dominated with uniform flow structure while the wall region is dominated with high fluctuations in solid concentration. Further, it was found that the entrance and developing flow sections of the riser exhibit high flow non-uniformities than the fully developed flow section of the riser. The flow non-uniformities in the entrance and developing flow section increase with increase in superficial gas velocity at constant solid flux. The wall region, from the entrance to the top sections of the riser along the axial direction exhibits both dilute and dense suspension flow.展开更多
目的探讨工作气压对管内等离子体放电光学现象以及Si/O-DLC(Si and O Incorporated DLC,Si/O-DLC)薄膜结构与性能的影响,为获得管内高质量、均匀的Si/O-DLC薄膜制备工艺技术提供指导。方法利用空心阴极等离子体增强化学气相沉积(Hollow ...目的探讨工作气压对管内等离子体放电光学现象以及Si/O-DLC(Si and O Incorporated DLC,Si/O-DLC)薄膜结构与性能的影响,为获得管内高质量、均匀的Si/O-DLC薄膜制备工艺技术提供指导。方法利用空心阴极等离子体增强化学气相沉积(Hollow Cathode Plasma Enhanced Chemical Vapor Deposition,HC-PECVD)技术,通过改变工作气压在管内沉积Si/O-DLC薄膜。利用高速摄像机记录并对比不同工作气压下管内等离子体放电光学现象。通过SPM、XPS和Raman光谱仪表征不同工作气压下薄膜的三维立体表面形貌和微观结构,并利用SEM、纳米压痕仪以及划痕测试系统,对比研究管内Si/O-DLC薄膜的硬度、弹性模量、膜基结合力以及沿管轴向的薄膜厚度分布。结果随着工作气压的上升,管径向中心处亮斑面积和光强先增大增强后趋于缩小暗淡。在不同工作气压下,均能够在管内获得表面光滑的Si/O-DLC薄膜,粗糙度为3~10 nm。随着工作气压的上升,管内Si/O-DLC薄膜的平均厚度从1.42μm增大到2.06μm,且沿管轴向的薄膜厚度分布均匀度从24%显著提高到65%;不同工作气压下管内Si/O-DLC薄膜沿管轴向平均硬度呈先增大后减小的趋势,总体平均硬度可达(14±1)GPa。管内Si/O-DLC薄膜在工作气压上升到25 mTorr时获得较高的平均膜基结合力。结论改变工作气压能够显著影响管内壁Si/O-DLC薄膜的结构与性能,当工作气压为25 m Torr时,在管内获得均匀性最优、结合力较高的Si/O-DLC薄膜。展开更多
文摘The combined effects of the magnetic field, permeable walls, Darcy velocity, and slip parameter on the steady flow of a fluid in a channel of uniform width are studied. The fluid flowing in the channel is assumed to be homogeneous, incompressible, and Newtonian. Analytical solutions are constructed for the governing equations using Beavers-Joseph slip boundary conditions. Effects of the magnetic field, permeability, Darcy velocity, and slip parameter on the axial velocity, slip velocity, and shear stress are discussed in detail. It is shown that the Hartmann number, Darcy velocity, porous parameter, and slip parameter play a vital role in altering the flow and in turn the shear stress.
文摘Statistical analysis of the entrance and wall dynamics of a high-flux gas-solid riser was done using solid concentration time series data collected from a 76 mm internal diameter and 10 m high riser of a CFB system with a twin-riser operated at 4.0 to 10.0 m/s gas velocity and 50 to 550 kg/m2s solids flux. Spent fluid catalytic cracking catalyst particles with 67 μm mean diameter and density of 1500 kg/m3 together with 70% to 80% humid air was used. Solid concentration data were analysed using code prepared using FORTRAN 2008 to get statistical parameters and plot their profiles. Results obtained show that the gas-solid suspension flow in the riser is dominated by low solid concentration in the centre region and high solid concentration in the wall region which forms a core-annulus flow structure. The mean solid concentration in the wall region decreases with riser height from the dense bottom section to less dense in the fully developed flow section at the top of the riser. The gas-solid suspension flow in the centre region is dominated with uniform flow structure while the wall region is dominated with high fluctuations in solid concentration. Further, it was found that the entrance and developing flow sections of the riser exhibit high flow non-uniformities than the fully developed flow section of the riser. The flow non-uniformities in the entrance and developing flow section increase with increase in superficial gas velocity at constant solid flux. The wall region, from the entrance to the top sections of the riser along the axial direction exhibits both dilute and dense suspension flow.
文摘目的探讨工作气压对管内等离子体放电光学现象以及Si/O-DLC(Si and O Incorporated DLC,Si/O-DLC)薄膜结构与性能的影响,为获得管内高质量、均匀的Si/O-DLC薄膜制备工艺技术提供指导。方法利用空心阴极等离子体增强化学气相沉积(Hollow Cathode Plasma Enhanced Chemical Vapor Deposition,HC-PECVD)技术,通过改变工作气压在管内沉积Si/O-DLC薄膜。利用高速摄像机记录并对比不同工作气压下管内等离子体放电光学现象。通过SPM、XPS和Raman光谱仪表征不同工作气压下薄膜的三维立体表面形貌和微观结构,并利用SEM、纳米压痕仪以及划痕测试系统,对比研究管内Si/O-DLC薄膜的硬度、弹性模量、膜基结合力以及沿管轴向的薄膜厚度分布。结果随着工作气压的上升,管径向中心处亮斑面积和光强先增大增强后趋于缩小暗淡。在不同工作气压下,均能够在管内获得表面光滑的Si/O-DLC薄膜,粗糙度为3~10 nm。随着工作气压的上升,管内Si/O-DLC薄膜的平均厚度从1.42μm增大到2.06μm,且沿管轴向的薄膜厚度分布均匀度从24%显著提高到65%;不同工作气压下管内Si/O-DLC薄膜沿管轴向平均硬度呈先增大后减小的趋势,总体平均硬度可达(14±1)GPa。管内Si/O-DLC薄膜在工作气压上升到25 mTorr时获得较高的平均膜基结合力。结论改变工作气压能够显著影响管内壁Si/O-DLC薄膜的结构与性能,当工作气压为25 m Torr时,在管内获得均匀性最优、结合力较高的Si/O-DLC薄膜。
