加压密相气力输送煤粉颗粒荷电特性研究

介绍了一种非接触式移动颗粒静电测试方法,并在加压密相气力输送实验装置上对质量浓度在128～230 kg/m3,气体表观速度在6～15 m/s条件下的煤粉颗粒荷电特性进行了实验研究.颗粒平均粒径为35.6μm.实验结果表明:粉体颗粒荷电指示值随着颗粒浓度的增加逐步增大,浓度在150～160 kg/m3之间时达到最大值,随后减小;指示值随着气体表观速度的增加而增大,而后趋于饱和值.     

带电沙尘暴对电磁波传播过程的影响

基于极化面电荷密度和瑞利散射理论,通过数值计算与仿真讨论了风沙静电场对沙粒光学性质的影响。数值结果表明:在考虑风沙静电场作用的情况下,沙粒对电磁波的散射效率随着电荷分布角的增加先增加后减小,而其对电磁波的吸收效率保持恒定,但其值远大于不考虑环境电场作用时的对应值。另外,随着沙尘浓度及其含水量的增加,沙尘暴对电磁波的衰减率增强。结果说明在沙尘暴遥感的研究中必须考虑到沙尘暴中的静电场作用。     

加压密相粉煤输送特性及稳定性研究

在高压气力输送试验台上,用氮气进行煤粉高压浓相气力输送试验研究.考察操作参数和粉体物性对煤粉质量流量和固气比等气力输送特征参数的影响,用信息熵分析试验过程中采集到的差压波动时间序列,建立信息熵和流动特性之间的关联.结果表明流动相图与SHANNON熵之间呈现较好的规律性.随着煤粉含水率的增大,煤粉的质量流量和压损减小,SHANNON熵值下降.随着输送压损的增大,SHANNON熵增大.     

碰撞参数对磁化电负性等离子体鞘层结构的影响

数值研究了离子马赫数的取值和碰撞参数对由热电子、热负离子和冷正离子构成的磁化电负性等离子体鞘层结构的影响.通过理论推导得到了鞘层模型的玻姆判据的表达式,并得到了不同离子马赫数情况下鞘层的正离子密度分布和净电荷分布曲线,还进一步得到了几个不同碰撞参数下鞘层的带电粒子密度、净电荷以及电势分布曲线.结果表明:离子马赫数取值不同对应不同的鞘层结构;碰撞使鞘层中正离子密度增加,使电子密度更快减小到零,对负离子密度分布影响不明显;碰撞使净电荷密度的峰值幅度增加并向鞘层边缘移动,使鞘层中电势值升高并使鞘层厚度减小.     

非均匀带电沙粒的电磁散射特性研究

基于瑞利近似推导了平面波入射下非均匀带电球形粒子的散射场及其散射截面,并通过数值仿真讨论了电荷非均匀分布对沙粒微分散射截面、散射效率的影响。数值结果表明:当沙粒表面电荷非均匀分布时,其微分散射截面呈明显空间分布,而电荷均匀分布时近似为各向同性散射;另外给定面电荷密度且电荷非均匀分布时带电沙粒散射效率远小于电荷均匀分布时的对应值,但在某些电荷分布角时恰好相反,随着沙粒带电量的增加其散射效率显著增加。由此说明在利用微波进行沙尘暴遥感或监测中需要同时考虑沙粒表面电荷分布规律及其携带电荷量的影响。     

有限长带电导体直线的电荷分布

通过3种方式给出有限长带电导体直线的电荷密度分布,结果表明电荷分布并不均匀.     

CdS掺Ti和Co几何结构及电子结构的密度泛函理论研究

采用基于密度泛函理论的第一性原理赝势平面波方法，对闪锌矿结构CdS和CdS：M（M=Ti，Co）几何结构、电荷分布、能带结构和电子态密度等进行了系统研究．几何结构研究对晶格参量进行了优化计算，Co和Ti原子掺入CdS后晶格常数均减小，晶格发生局部畸变．电荷密度计算表明，对于掺Co体系，近邻的S原子电荷分布变化明显，即有更多电子转移到S原子，同时次近邻Cd原子周围的电子分布也受到影响；对于Ti体系，邻近S原子电荷分布变化不明显，次近邻Cd原子周围电荷也没有重新分布．能带结构和态密度分析表明，由于Co3d和Ti3d电子的引入，CdS：Co成为铁磁半导体，而CdS：Ti为简并半导体．     

酮缺陷对中性和带电六卟啉芳香性影响的直接可视化研究

利用含时密度泛函理论研究了酮缺陷对中性和带电六卟啉芳香性的影响,并使用多维可视化技术给出了该体系基态电荷分布和电子跃迁的直观图像. 研究结果表明,芳香性是决定这类体系基态密立根电荷分布的主要因素;酮缺陷效应使得体系基态的密立根电荷分布更多地局域在六卟啉基团上,在这类体系的五氟苯基取代基上密立根电荷布居较少,同时使得体系的芳香性发生改变. 进一步,通过计算体系的跃迁密度和电荷差分密度,可视化了酮缺陷对中性和带电六卟啉芳香性的影响. 结果表明,酮缺陷加强了体系电荷转移的能力.     

粉末颗粒气力加注特性实验研究

粉末发动机是以粉末颗粒为燃料的新型发动机,具有多次起动和推力调节的功能.粉末加注是粉末发动机实验组织过程中的重要环节.本研究通过搭建粉末供应系统开展粉末气力加注实验,研究对比了集粉箱加注位置、流化气量对粉末气力加注特性的影响.考虑了供粉过程中储箱内粉末堆积密度的动态变化,并建立了相应的计算方法,同时还采用控制系统理论揭示了储箱内粉末堆积密度的变化规律.结果表明:在相同条件下,较大的流化气量有利于加注过程稳定,但集粉箱加注率较低;气力加注方式下集粉箱内的粉末堆积密度大于储箱内初始堆积密度;采用较小的流化气量与集粉箱壁面切向加注方式有利于提高粉末粒径分布均匀性;集粉箱壁面切向加注方式下,流化气量较小时储箱内粉末的堆积密度是先增大后减小,且堆积密度最终值小于初始值,而流化气量较大时,储箱内粉末的堆积密度是先增大后减小再增大后减小,且堆积密度最终值大于初始值;储箱内粉末堆积密度的动态变化过程类似于欠阻尼二阶系统,流化气量较小时系统阻尼系数较小,而流化气量较大时系统阻尼系数较大,且是一个变阻尼过程.     

激光全散射法测量燃煤颗粒物浓度的实验研究

本研究在激光全散射法颗粒物浓度检测系统上进行了不同性质、浓度燃煤飞灰颗粒的质量浓度测量实验。结果显示,联合全散射法颗粒物浓度检测系统和反演计算方法能良好的测算标准颗粒的质量浓度,误差约为7%。对于燃煤飞灰颗粒,测算结果能反映气流中颗粒浓度的变化,然而测算值高于真实值约19.3%~27.2%。并且,对除尘器前级电场飞灰的测算偏差大于第四电场飞灰。进一步的理论计算结果表明,随颗粒粒径增大,散射光分布逐步向前向(即0°方向)集中,导致光电探测器在收集透射光的同时收集部分前向散射光,使得反演计算值大于真实值。而前级电场飞灰中含有更多的大粒径、非球形颗粒且粒径分布范围更宽,偏离了反演算法的假定条件,导致对测算偏差增大。     

Using Flow Relaxography to Elucidate Flow Relaxivity

We have investigated the theoretical and experimental linear dependence of the reciprocal of the apparent longitudinal relaxation time [(T^*₁)⁻¹] of the NMR signal from spins in a flowing fluid on the volume flow rate,F_v, the so-calledinflow effect.We refer to the coefficient of this dependence as the longitudinalflow relaxivity, r_1F. A very simple model predicts that, under a range of conditions pertinent to modern flow studies and perfusion imaging experiments,r_1Fis controlled by the volume of the fluid in which the magnetization is perturbed by pulsed RF inversion or saturation, not the detection volume, and that it can be approximated as the reciprocal of half of the inversion volume. Phantom sample experiments, using a new, quantitative approach that we callflow relaxography,confirm the general predictions of this simple model. There are two intriguing implications of these findings for general NMR flow studies as well as for medical applications. It should be possible to vary the value ofr_1Fby simply (noninvasively) adjusting the inversion slice thickness, and thus measure the value of (blood¹H₂O, for example)F_vin a vessel without changingF_v, from the resultant varyingT^*₁values. Also, it should be possible to extrapolate to the intrinsicT₁value of the fluid signal (as if it were stationary), without altering or stopping the flow. Again, these are quite successful in phantom sample studies. Imaging versions of the flow relaxographic experiments are also possible. The twin goals of flow studies in medical MRI are the quantitative discrimination of the signals from flowing and nonflowing spins, and the accurate measurement of the flow rate of the former.     

Arc-Gas Flow Interactions in a Double-Nozzle Flow System

The physical phenomena in cold and arc heated double-nozzle gas flows have been investigated for SF6 by interference and shadow methods. The cold-flow phenomena are discussed as a basis for a better understanding of the arc-gas flow interactions, their interference pattern is clearly interpreted: the observed fringes, which also can be calculated theoretically, are lines of constant flow velocity. In the case of arc heated flows a sharp distinction is made for the first time between different types of arc-gas flow interactions. At low peak currents the interference pattern still shows a cold gas flow around the arc. At higher current levels a fringe system, which indicates a density reduction, expands into the volume around the nozzles; however, the flow is still directed towards the gap between the nozzles. In contrast to this case the strongest form of interaction is characterized by the appearance of arc heated gas, which flows turbulently back into the high-pressure volume. The radial temperature distribution for a special arc has been calculated theoretically and is discussed in detail.     

Mean Curvature Flow in a Ricci Flow Background

Following work of Ecker (Comm Anal Geom 15:1025–1061, 2007), we consider a weighted Gibbons-Hawking-York functional on a Riemannian manifold-with-boundary. We compute its variational properties and its time derivative under Perelman’s modified Ricci flow. The answer has a boundary term which involves an extension of Hamilton’s differential Harnack expression for the mean curvature flow in Euclidean space. We also derive the evolution equations for the second fundamental form and the mean curvature, under a mean curvature flow in a Ricci flow background. In the case of a gradient Ricci soliton background, we discuss mean curvature solitons and Huisken monotonicity.     

转捩与湍流对激波边界层干扰及底部流动结构的影响

为研究转捩与湍流对激波边界层干扰及底部流动结构的影响,文章选取了二维与三维高超声速双斜面进气道模型与大钝头着陆器模型,并使用γ-Re_θ转捩模型开展数值模拟研究.研究表明,对于二维进气道模型,随着前缘钝度的增加,激波边界层干扰位置前移,分离区变大,与层流流动情况相比,有转捩流动发生时,激波边界层干扰位置后移,同时分离流动强度变弱,分离区缩小;对于三维进气道模型,其拐角附近的分离流动呈现明显的三维特征,转捩流动也存在三维流动结构,与静风洞状态相比,噪音风洞状态下,有转捩流动发生,对壁面热流影响较大,对激波系影响很小.对于着陆器模型,底部流动发生转捩,使得底部流动由不稳定非定常的流动结构变为稳定定常的流动结构,这有益于姿态控制设计.      

跨音速自然层流翼型多目标优化设计

应用多目标优化方法在推迟翼型转捩位置的同时,优化激波控制鼓包的位置和外形来减小波阻.经过优化得到多目标问题的Pareto阵面解,通过对其上翼型的气动性能分析发现:优化后翼型的层流区域及激波强度较初始翼型均有改善.结果表明本文方法可以有效地解决层流翼型设计过程中转捩位置和激波强度之间的矛盾.     

Stochastic Flow Cascades

We introduce and explore a Stochastic Flow Cascade (SFC) model: A general statistical model for the unidirectional flow through a tandem array of heterogeneous filters. Examples include the flow of: (i) liquid through heterogeneous porous layers; (ii) shocks through tandem shot noise systems; (iii) signals through tandem communication filters. The SFC model combines together the Langevin equation, convolution filters and moving averages, and Poissonian randomizations. A comprehensive analysis of the SFC model is carried out, yielding closed-form results. Lévy laws are shown to universally emerge from the SFC model, and characterize both heavy tailed retention times (Noah effect) and long-ranged correlations (Joseph effect).     

Flow of clays

Recent experimental and theoretical research into physical phenomena in clays is reviewed. Clays’ present place in the context of modern materials science is briefly discussed, and illustrated through the rich behavior recently displayed in this physical model system. We will show that in order to understand macroscopic flow behaviors in these systems, it is crucial to know the underlying nanostructures in detail. With the clay nanostructural basis at hand, we will review recent advances in clay systems from the geological example of quick clay flows and avalanches, to materials science and the stability, strength and flow of smart electrorheological clay structures. In the case of natural quick clay, there is now hope of establishing a protocol for avalanche preditction based on rheological sample data. In materials science, the use of electric fields together with flow in order to improve the processing of clay composite materials may open new unexplored avenues. We will finally discuss that due to the interplay of van der Waals and electrostatic forces screened by ions at the nanoscale, clays may either form a glass, or a gel and thus give fundamental insights into the elusive questions related to materials universal aging flow dynamics.     

Simplicial Ricci Flow

We construct a discrete form of Hamilton’s Ricci flow (RF) equations for a d-dimensional piecewise flat simplicial geometry, ${{\mathcal S}}$ . These new algebraic equations are derived using the discrete formulation of Einstein’s theory of general relativity known as Regge calculus. A Regge–Ricci flow (RRF) equation can be associated to each edge, ?, of a simplicial lattice. In defining this equation, we find it convenient to utilize both the simplicial lattice ${{\mathcal S}}$ and its circumcentric dual lattice, ${{\mathcal S}^*}$ . In particular, the RRF equation associated to ? is naturally defined on a d-dimensional hybrid block connecting ? with its (d?1)-dimensional circumcentric dual cell, ? ^*. We show that this equation is expressed as the proportionality between (1) the simplicial Ricci tensor, Rc _? , associated with the edge ${\ell\in{\mathcal S}}$ , and (2) a certain volume weighted average of the fractional rate of change of the edges, ${\lambda\in \ell^*}$ , of the circumcentric dual lattice, ${{\mathcal S}^*}$ , that are in the dual of ?. The inherent orthogonality between elements of ${\mathcal S}$ and their duals in ${{\mathcal S}^*}$ provide a simple geometric representation of Hamilton’s RF equations. In this paper we utilize the well established theories of Regge calculus, or equivalently discrete exterior calculus, to construct these equations. We solve these equations for a few illustrative examples.     

带通道插件管道流磁流体动力学效应的数值模拟

采用二维完全发展流模型对聚变反应堆包层带通道插件和压力平衡槽隙的矩形磁流体管流的MHD效应进行数值模拟,分析速度分布,MHD压降随哈德曼数以及通道插件的电导率的变化规律.与无插件磁流体管流相比,带绝缘通道插件管流MHD压降显著降低,MHD压降随哈德曼数的增加而减小,通道插件材料的电导率增加MHD压降系数减小.压力平衡槽隙处的回流与通道插件的电导率有关.在宏观上计算结果与实验结果和简化理论结果一致.