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1.
工业过程中粉体颗粒不可避免地会相互摩擦碰撞而荷电. 荷电颗粒的存在可能会危害正常的工业生产过程, 也可能对工业过程起促进作用. 因此, 荷电粉体颗粒及其特性受到了广泛的关注, 但目前对粉体颗粒的荷电机理依然缺乏透彻的了解, 尤其是在气固两相流动中的粉体颗粒荷电现象. 事实上, 工业中存在的粉体颗粒的运动都受到流体的影响, 是典型的气固两相流系统, 流体对粉体颗粒的作用使粉体颗粒接触的荷电现象变得更为复杂, 因此从两相流动的观点来研究粉体颗粒荷电的物理本质就显得越来越重要. 本文介绍了工业过程中的几种不同类型的粉体颗粒荷电行为, 回顾了颗粒的荷电机理与描述颗粒荷电的数学模型. 对于工业过程中颗粒的荷电现象及颗粒在多相流体中的动力学行为, 介绍了研究颗粒受流体影响时荷电特性的数值模拟方法. 本文旨在对粉体颗粒的荷电机理、应用以及研究方法进行梳理与探讨, 为正确认识工业过程中粉体颗粒的荷电现象并加以控制利用提供理论借鉴. 相似文献
2.
针对离散颗粒模型和欧拉-欧拉双流体模型在求解气粒两相流动问题中存在的不足,提出了一种新方法——SPH-FVM耦合方法,并应用于风沙运动过程的数值模拟计算.新方法基于拟流体模型,采用光滑粒子流体动力学方法(SPH)对离散颗粒相进行求解,追踪单颗粒运动轨迹,采用有限体积法(FVM)求解连续气体相,捕捉流场特性,两相间通过曳力、压力梯度、体积分数等参量进行耦合,建立了两种不同坐标系下方法间的耦合框架.对SPH粒子所承载的物质属性进行了重定义,改造成了适用于离散颗粒相求解的光滑离散颗粒流体动力学模型(SDPH),阐述了SPH粒子与离散相中颗粒之间的关系,推导得到了拟流体SPH离散方程组.模拟了风沙运动中沙粒跃移过程和自由来流风速作用下沙粒的运动过程以及沙丘在风力作用下缓慢向前蠕移的过程,分析了颗粒的运动轨迹,流场中沙粒水平速度分布规律以及气体速度场在沙粒反作用下的变化情况等,与实验结果相符合,结果表明该方法不仅精度较高,而且计算量较小,适于求解风沙运动问题乃至其他气粒两相流动问题. 相似文献
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本文采用一种简易制备静电场样品的方法,基于以下物理事实:一个置于薄导电碳膜上的非导电粒子,例如直径为0.31μm聚乙烯乳剂小球,在电镜中观察时,由于静电积累效应,它将成为一个荷电体,很显然,这个荷电体带有正电量Q,并能用一个点电荷场来模拟这个合成电场.采用这个模型,能用电子全息法观测由该点电荷所形成的静电场分布及荷电量的大小. 相似文献
5.
绝缘颗粒系统的摩擦带电现象是一种普遍现象,但至今仍未得到很好的认识.月球及火星表面漂浮着大量尘埃颗粒,这将严重影响探测设备的太阳能帆板、散热和观察系统等的正常工作.近年来,电帘除尘方法被认为是在月表进行尘埃防护的有效手段,研究表明颗粒表面摩擦带电对月尘静电来源贡献最大,因此正确理解颗粒摩擦带电的机理对分析尘埃颗粒的运动规律至关重要.本文建立了一个基于高能态电子假定的分析模型来预测颗粒间的摩擦电荷分布.计算了颗粒摩擦生电与颗粒粒度的依赖关系,以及粒度范围对摩擦电荷产生的概率大小的影响.揭示了电荷分布的一个上限,并讨论了可能的原因.对粒子碰撞过程中的电荷转移进行了粒子动力学模拟,验证了理论预测结果. 相似文献
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给出求解双向耦合可压缩气固两相流的间断有限元方法,对所得到的气固两相流方程组不需要采用分裂的方法离散,对气相、颗粒相方程及其对流部分和源项可以统一处理,两相都采用基于近似Riemann解的数值通量.数值模拟低压含尘激波管内的两相非平衡流动,并与平衡流、冻结流的结果进行比较.分析颗粒相的存在对气体运动的影响,及激波后松弛区域内两相间相互作用规律.发现颗粒质量比决定两相平衡后的最终状态,而颗粒直径决定两相流从非平衡到平衡的过渡过程,即不同尺寸颗粒对应的驰豫时间、松弛距离不同.结果表明:本文提出的计算方法对求解可压缩气固两相流是可行的,为研究复杂的气固两相流动问题奠定了基础. 相似文献
8.
风沙运动的DPM数值模拟 总被引:3,自引:0,他引:3
采用离散颗粒模型对风沙气固两相流动进行了数值计算.在该模型中,采用体平均的Navier-Stokes方程来描述气相的运动,对离散颗粒采用拉格朗日方法模拟,求解颗粒运动方程.采用硬球模型描述颗粒问碰撞作用.计算结果表明,沙粒平均水平速度廓线在0.02 m以上高度可以表示为按对数函数或幂函数规律增加,在0.02 m以下则发生偏离;在大于0.02 m的高度,输沙通量随高度按指数规律衰减,而在地面附近由于颗粒蠕移的影响发生偏离,这与已有文献结果一致。本文的模拟有助于风沙运动规律的研究与掌握。 相似文献
9.
风沙跃移中颗粒与多粒径床面碰撞的数值模拟 总被引:3,自引:0,他引:3
采用考虑颗粒碰撞的欧拉-拉格朗日数值模拟方法,对风沙跃移中颗粒冲击多粒径床面的碰撞过程进行了数值计算。在模型中,对气相采用欧拉方法建立控制方程,对离散颗粒采用拉格朗日方法模拟,颗粒间碰撞作用采用软球模型描述。计算结果表明该模型可以模拟风沙运动中颗粒冲击多粒径床面的动态运动过程。而且在多粒径非均匀床面上的颗粒起跳具有较大的随机性。这有助于进一步揭示风沙运动中颗粒碰撞起跳机理。 相似文献
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基于水的电离理论和颗粒动力学理论,提出了一种风沙运动颗粒碰撞的静电起电模型:颗粒表面覆盖有水分子薄层,颗粒间的碰撞导致能量转移和颗粒温度变化;水电离生成H3O+和OH-离子,当两个温度不同或水分子薄层正(负)离子浓度不同的颗粒相接触时,H3O+比OH-以更快地速度从浓度高的地方向浓度低的地方迁移. 在动力学的模拟计算中采用0.1mm,0.2mm和0.4mm三种粒径的沙粒以示沙
关键词:
风沙运动
静电
颗粒动力学
尘卷风 相似文献
12.
In a wind-blown sand layer, it has been found that wind transport of
particles is always associated with separation of electric charge. This
electrification in turn produces some electrostatic forces in addition to
the gravitational and fluid friction forces that affect the movement of
saltating sand particles, further, the wind-blown sand saltation. To
evaluate this effect quantitatively, this paper presents a simulation of
evolution of wind-blown sand grains after the electrostatic forces exerted
on the grains are taken into account in the wind feedback mechanism of
wind-blown saltation. That is, the coupling interaction between the wind
flow and the saltating sand particles is employed in the simulation to the
non-stationary wind and sand flows when considering fluid drag, gravitation,
and a kind of electrostatic force generated from a distribution of electric
field changing with time in the evolution process of the sand saltation. On
the basis of the proposed simulation model, a numerical program is given to
perform the simulation of this dynamic process and some characteristic
quantities, e.g., duration of the system to reach the steady state, and
curves of the saltating grain number, grain transport rate, mass-flux
profile, and wind profile varying with time during the non-stationary
evolution are displayed. The obtained numerical results exhibit that the
electrostatic force is closely related to the average charge-to-mass ratio
of sand particles and has obvious influence on these characteristic
quantities. The obtained results also show that the duration of the system
to reach the steady state, the sand transport rate and the mass flux profile
coincide well with experimental results by Shao and Raupach (1992) when the
average charge-to-mass ratio of sand particles is 60 μC/kg for the sand
particles with average diameter of 0.25 mm. When the average charge-to-mass
ratios of sand particles are taken as some other certain values, the
calculation results still show that the mass flux profiles are well in
agreement with the experimental data by Rasmussen and Mikkelsen (1998) for
another category of sand particles, which tell us that the electrostatic
force is one of main factors that have to be considered in the research of
mechanism of wind-blown sand saltation. 相似文献
13.
Electromagnetic scattering of charged particles in a strong wind-blown sand electric field 下载免费PDF全文
《中国物理 B》2019,(3)
Some field experimental results have shown that the moving sands or dust aerosols in nature are usually electrified,and those charged particles also produce a strong electric field in air, which is named as wind-blown sand electric field.Some scholars have pointed out that the net charge on the particle significantly enhances its electromagnetic(EM) extinction properties, but up to now, there is no conclusive research on the effect of the environmental electric field. Based on the extended Mie theory, the effect of the electric field in a sandstorm on the EM attenuation properties of the charged larger dust particle is studied. The numerical results indicate that the environmental electric field also has a great influence on the particle's optical properties, and the stronger the electric field, the bigger the effect. In addition, the charged angle, the charge density, and the particle radius all have a specific impact on the charged particle's optical properties. 相似文献
14.
研究风沙流对高压绝缘子电位和电场分布的影响,基于有限体积法建立绝缘子风沙气固两相流模型和风沙天气下绝缘子的风-沙-电耦合场模型,计算不同风沙天气下绝缘子表面沙尘的空间分布和沉积及其对绝缘子沿面电位和电场的影响,结果表明:风沙天气下绝缘子沿面电位和电场畸变受风速和粒径影响显著,电位的畸变幅度随风速和粒径的增加而升高,电场的畸变幅度随风速和粒径的增大而减少;风沙天气下绝缘子表面不同的沙尘空间分布和沉积导致绝缘子不同位置沿面电位和电场畸变不同. 相似文献
15.
The dust emission models to date cannot describe the relation between the transport rate of different sized grains and their
grain size composition in soil surface, so Aeolian grain transport on a soil-like bed composed of fine sand and silt powder
was measured in a wind tunnel. Six types of soil-like beds with different silt fractions have been tested in this experiment.
The mass flux profiles of silt dust and sand grains are much different due to their different motion modes. Analysis of the
vertical distribution of the powder and sand grains reveals that for a given soil bed, the ratio of the horizontal dust flux
to the horizontal sand flux is directly proportional to their mass ratio in the bed. The dust flux is closely linked to the
sand flux by the bombardment mechanism. For a given wind velocity and grain size of the bed, the slopes of the vertical mass
flux profiles of sand grains larger than 100 μm are nearly equal in a log-linear plot and the ratio between the fraction of
transport rate of each size group to the whole transport rate and the mass fraction of each size group in the bed is a constant
only dependent on grain size. With this law, the transport rate of dust and different sized grains can be related with the
grain size composition in the soil surface.
Supported by the National Natural Science Foundation of China (Grant No. 50706031) and the Natural Science Foundation of Shanxi
Province of China (Grant No. 2008021005) 相似文献
16.
Balbás Gambra M Rohr C Gruber K Hermann BA Franosch T 《The European physical journal. E, Soft matter》2012,35(3):1-8
The triboelectric charging of collision particles is essential to understand sand electrification in wind-blown sand fluxes. The physical model of electron trapped in high-energy states has been proposed to explain the triboelectric charging between identical insulating granular materials. In this study we propose an improved triboelectric charging model which combines the soft sphere model and the trapped electron model to calculate the net charge transfer during particles' collisions. Based on our charging model, we investigate the sand electrification of wind-blown sand, such as the charge flux varying with height, the charge-to-mass ratio of wind-blown sand, and the equilibrium time that the charge takes to approach a stable state. Numerical simulation results of the averaged charge-to-mass ratio in wind-blown sand fluxes are in good agreement with the experimental data. 相似文献
17.
《Journal of Electrostatics》2007,65(10-11):631-638
The physics that initiate and sustain tornados and dust devils is still under investigation. Forces that operate throughout a wide range of scales and could contribute to atmospheric vortex phenomena are the Lorentz force and the force of electric fields. The Lorentz force results in a circular motion of charged particles in a magnetic field. An electric field will pull or repel a charged particle in the direction of the field. This paper will demonstrate that the Lorentz force and the force of electric fields, acting on charged particles that exist in atmospheric vortex phenomena, plausibly contribute to the set of physics that will explain tornados and other atmospheric vortex phenomena. 相似文献
18.
Numerical simulation and experimental validation of multiphysics field coupling mechanisms for a high power ICP wind tunnel 下载免费PDF全文
《中国物理 B》2021,30(6):65201-065201
We take the established inductively coupled plasma(ICP) wind tunnel as a research object to investigate the thermal protection system of re-entry vehicles. A 1.2-MW high power ICP wind tunnel is studied through numerical simulation and experimental validation. The distribution characteristics and interaction mechanism of the flow field and electromagnetic field of the ICP wind tunnel are investigated using the multi-field coupling method of flow, electromagnetic, chemical, and thermodynamic field. The accuracy of the numerical simulation is validated by comparing the experimental results with the simulation results. Thereafter, the wind tunnel pressure, air velocity, electron density, Joule heating rate, Lorentz force, and electric field intensity obtained using the simulation are analyzed and discussed. The results indicate that for the 1.2-MW ICP wind tunnel, the maximum values of temperature, pressure, electron number density, and other parameters are observed during coil heating. The influence of the radial Lorentz force on the momentum transfer is stronger than that of the axial Lorentz force. The electron number density at the central axis and the amplitude and position of the Joule heating rate are affected by the radial Lorentz force. Moreover, the plasma in the wind tunnel is constantly in the subsonic flow state, and a strong eddy flow is easily generated at the inlet of the wind tunnel. 相似文献