悬浮微粒在被加热多孔介质内的沉积与运移特性

通过建立沿管壁恒热流加热的渗流实验系统,实验研究了悬浮颗粒在饱和多孔介质内以及入口界面处的沉积和运移特性。着重研究了有无加热条件,以及不同加热温差,相同多孔介质和进口悬浮液浓度情况下,实验段入口界面处与内部的颗粒沉积量变化,以及沿程不同位置处的压力变化。并对实验过程中的渗流稳定性及各测点温度和多孔介质段渗透系数进行了分析。结果表明:相对渗透率k_t/k₀在不同温差下有明显不同;多孔介质与进口流体界面处的沉积量随温差的增大而增加,沉积结构的稳定性降低;多孔介质段颗粒沉积强度随温差的增大而增大,实验结果可为今后的理论分析提供验证依据。     

水平导管内颗粒料层中的热渗透现象研究

本文针对水平导管内填充颗粒料层中的高温气体渗流现象,采用局部非平衡假设建立了多孔介质渗流传热物理数学模型并进行了数值计算。研究了不同情况下导管内填充多孔介质中的流速、气固温度和压力分布。计算结果表明,高温气体对导管内颗粒料层的热渗透作用主要是在渗流入口端区域,增大入口渗流速度以及减少给料量,导致气固温度沿轴向下降速度减慢,热渗透深度扩大,热渗透作用区域内的物料温度水平提高。在热渗透作用区域,孔隙率对流场和压力损失有很大的影响。研究结果对于移动颗粒反应器和输送机的设计与运行具有一定的参考作用。     

颗粒直径对吸附分离影响的数值模拟

基于Fluent的多孔介质模型,建立了变压吸附制氧发生器的立式填充床模型。采用用户自定义函数功能,以反映吸附传质、传热,并将多孔介质单相模型整合为更精确的气固两相耦合模型。在此基础上,模拟了吸附颗粒直径对气相压力、速度、床层压降以及氧气分离浓度、回收率等参数的影响情况。结果表明：床层压降随颗粒直径的增大而减小;床层对入口急流的抗穿透性能随颗粒直径的增大而减小;相同条件下,采用较小颗粒直径能够提高氧气分离浓度、回收率,原因在于小颗粒直径降低了床层内气体的流速,增加了吸附时间,促进了吸附的进行。     

微观储层岩石内孔隙率对砂粒流动的影响研究

请采用DEM-CFD方法对微尺度储层岩石内沙粒流动特性进行模拟。建立了复杂形状的微通道模型,通过改变微通道的孔隙率,分析了沙粒在微通道中的速度分布、停留时间以及颗粒拟温度的分布。模拟结果表明,在形状复杂并且孔隙率低的情况下,沙粒极易被堵塞、沉积在微通道底部。随着孔隙率的增加,停留时间呈上升趋势;平均颗粒拟温度先增加后减小;颗粒轴向速度脉动幅度减小;而且颗粒接触力的平均值和标准方差也减小并且范围集中。     

基于COMSOL的多孔介质热-流-变形耦合数值模拟

针对在稠油热采过程中,将高温高压流体注入油藏多孔介质所引起的岩石骨架变形、储层压力增大和油藏温度变化等问题,基于达西定律,应用连续介质力学和能量守恒定律,建立了稠油热采过程中的热-流-变形耦合方程,对基于REV尺度建立的多孔介质进行数值模拟计算和分析。结果表明：增加渗透率对多孔介质的效果优于增加入口温度和压力;增加入口压力能够增加热量传递速度;增加入口温度会导致骨架变形量增大,岩石破裂。     

多孔介质热流耦合传热模拟研究

针对稠油热采过程中高温高压流体注入油藏多孔介质引起的温度场和速度场的变化情况,以达西定律为基础,采用有限体积法建立多孔介质热流耦合方程。基于REV尺度多孔介质模型进行模拟计算,研究多孔介质的渗透率和体积分数,以及热采过程中热流体的注入压力,对多孔介质内热流耦合传热过程的影响。结果表明:增加渗透率对多孔介质传热的效果优于增加入口压力,固体体积分数增大,增加热阻,导致传热效果降低。增大注入热流体压力,能够增加热量传递速度。     

高温金属熔液在旋转多孔介质内的渗流传热过程

针对转动坐标系中铝熔液在SiC多孔介质内的流动传热现象 ,考虑离心力对渗流传热过程的影响 ,采用局部非热平衡假设建立多孔介质渗流传热数理模型 ,研究不同工况下流体的流速、压力损失及铝熔液和多孔介质的温度变化 .计算结果表明 :在渗透区域 ,液固两相存在温差 ,且液固温差随渗透界面的移动而减小 ;在非渗透区域 ,固体的温度曲线基本不变 .离心转速或孔隙率的增加都使渗透前沿区域液固两相温差增大 .孔隙率对流场和压力损失有较大影响.     

移动颗粒床中高温气体渗流传热数值计算

针对移动颗粒床中物料层内的高温气体渗流传热现象 ,考虑渗流与传热的相互作用 ,采用局部非热平衡假设建立了多孔介质渗流传热物理数学模型并进行了数值计算 .研究了不同情况下床内填充多孔介质中的流速、气固温度和床层压力损失 .计算结果表明 ,高温热气对移动床颗粒料层的热渗透主要发生在渗流入口端区域 ,增大入口渗流速度以及减小床层物料下移速度将导致物料温度沿床高慢速下降 ,热渗透深度扩大 ,热渗透作用区域内的物料温度水平提高 .在热渗透作用区域 ,孔隙率对流场和压力损失有很大的影响 .研究结果对于移动颗粒床反应器的设计与运行具有一定的参考作用     

填充沸石的大型离子交换柱内流场模拟

针对沸石法海水富钾工程化放大中的关键问题,采用Fluent中多孔介质模型对填充沸石的大型离子交换柱内流场进行了模拟研究。主要考察了沸石的孔隙率和颗粒直径、海水进口速度、沸石柱长径比以及柱内形成的沸石层凹坑等条件对离子交换柱内流体流动的影响,结果发现：孔隙率和颗粒直径直接关系到沸石层内流体的速度分布,海水进口速度、沸石柱长径比等条件对沸石层内的流体流动并无显著影响;而在孔隙率和颗粒直径确定的条件下,由于海水冲击形成的凹坑对沸石层内流体影响较大,会在凹坑两侧形成滞留区,进而影响沸石对海水中钾的吸附。根据模拟结果优化了填充材料、设备结构以及工艺等参数,为沸石法海水富钾关键装备进一步扩大规模提供了理论支撑。     

孔隙分布对多孔介质内流动和传热的影响

采用Sierpinski地毯分形技术建立多孔介质内流动和传热模型,通过改变固体基质位置研究了孔隙分布结构对多孔介质内流动特性和热效率的影响,3种孔隙分布为每分形一次固体基质分布在中心位置(A)、分布在中上方(B)和分布在右上方(C),当流体稳定流过多孔介质时,不同的孔隙分布表现出不同流动和传热特性. 结果表明,孔隙分布是影响多孔介质传输特性和传热效率的重要因素,无量纲渗透率k*C>k*B>k*A,多孔介质孔隙率大于0.8时更明显;流体流过不同孔隙分布的多孔介质时,相同孔隙率时与流体接触的固体基质面积A>B>C,传热效果A最佳、C最差. 孔隙分布影响了无量纲局部熵产率,在3种孔隙分布下用Be表示的热传导引起的熵产率占主导.     

Numerical simulation of fine particle liquid–solid flow in porous media based on LBM-IBM-DEM

Fine particle liquid–solid flow in porous media is involved in many industrial processes such as oil exploitation, geothermal reinjection, and filtration systems. It is of great significance to master the behaviours of the fine particle liquid–solid flow in porous media. At present, there are few studies on the influences of the migration of fine particles on the flow field in porous media, and the effects of the porosity of porous media and inlet fluid velocity on the migration behaviours of fine particles in porous media. In this paper, a liquid–solid flow model was established based on the lattice Boltzmann method (LBM)-immersed boundary method (IBM)-distinct element method (DEM) and verified by the classical Drag Kiss Tumble (DKT) phenomena and flow around a cylinder successfully. In this model, the interaction between solid particles is analyzed using the distinct element method, and the interaction between fine particles and flow field is handled by IBM. Then, the migration and blockage of fine particles in porous media was studied using this model. It is found that, in addition to the blockage, a large amount of blocked-surface sliding-separation occur in fine particles. At the same time, the decrease in porosity increases the damage degree of fine particles on the permeability. The porosity exerts great influence on the penetration rate and dispersion behaviour of fine particles. The inlet fluid velocity mainly affects the residence time of fine particles and the average velocity of motion in the direction perpendicular to the main flow direction.     

Effects of geometric and operating parameters and feed characters on the motion of solid particles in hydrocyclones

The effects of geometric and operating parameters and feed characters on the motion of solid particles in hydrocyclones were experimentally investigated by using a new type of laser surveying instrument named particle dynamics analyzer. The absolute radial velocity of solid particles decreases with increasing the positional radius, and the axial distribution curves of the particle radial velocity are parabolic. The particle radial velocity increases with increasing the inlet pressure or with increasing the diameter of the underflow pipe. When the particle density or the particle size increases, the absolute radial velocity of the solid particles decreases. The particle radial velocity also decreases with increasing the feed particle concentration. The axial distribution curves of the particle axial velocity are also parabolic. The axial velocity in the inner helical flow increases with the increase of the flow rate of overflow; while that in the lower positions in the outer helical flow increases with increasing the flow rate of underflow.     

Hydrodynamics of binary fluidization in a riser: CFD simulation using two granular temperatures

A new computational fluid-dynamic (CFD) model with a separate granular temperature (2/3 random particle kinetic energy per unit of mass) equation for each phase or particle size was developed using constitutive equations derived earlier by Huilin, Gidaspow and Manger. In agreement with the experiment and model of Mathiesen, Solberg and Hjertager the new model computes the observed core-annular flow regime. It predicts the trends of the observed radial and axial particle diameter distributions. For elastic particles the computed particle velocity distributions are parabolic. They are close to the laminar type approximate analytical solution for flow in a pipe, where the mean velocity equals the inlet flux divided by the particle density and volume fraction. The computed turbulent intensity is lower for large particles than for small particles, as measured. This is in agreement with an approximate analytical solution for the granular temperature in the developed flow region of a riser for elastic particles. Computations show that for sufficiently inelastic particles the granular temperature in the center can be lower than near the wall resembling the measured particle fluctuating velocity distribution.     

Particle Deposition in Laminar Crossflow Filtration of Power Law Slurry

Abstract

A theoretical model for predicting the probability of particle deposition in crossflow filtration of power law slurry is developed. The model is based on the critical angle of friction between depositing particles, which can be estimated by analyzing the forces exerted on the particles. The binding force between the particles due to polymer adsorption plays an important role in the particle deposition. The smaller the flow behavior index of the slurry is, the larger the binding force and the higher the probability of particle deposition will be. The effects of operating conditions such as the crossflow velocity of the slurry and the filtration rate on the probability of particle deposition are also discussed in depth. The calculated values of the probability of particle deposition agree fairly well with the experimental data. A program is designed to simulate the packing structure and the porosity at the cake surface. The porosity increases not only with the increase of the crossflow velocity, but also with the increase of the flow behavior index of the power law slurry.     

Simulation analysis of gas–solid flow characteristics and water evaporation in flue gas semi-dry desulphurization process based on CPFD method

The gas–solids flow in an industrial-scale semi-dry method desulphurization tower is simulated by the computational particle fluid dynamics (CPFD) approach. Compared with previous studies on desulphurization towers, this study focuses on analyzing particle distribution characteristics such as particle volume fraction, temperature distribution, and residence time. The simulation fully considered the particle–fluid, particle–particle, and particle–wall interactions in the desulphurization tower. Based on these considerations, the effects of flue gas inlet velocity and temperature on the gas–solid distribution characteristics of the desulphurization tower are simulated. An optimization scheme for adjusting the gas–solid flow in the desulphurization tower is proposed. The research results show that the error between the CPFD simulation data and experimental data is small and the changing trend is consistent. The particles in the bed of the desulphurization tower show a typical core–annulus flow. The distribution of gas and particles in the bed has a serious deviation with the increase of the flue gas inlet velocity and temperature. As the axial height of the desulphurization tower increases, the flue gas velocity, temperature, particle concentration, and water vapour distribution in the bed become more uniform. The relatively stable operating conditions for the gas–solid flow in the desulphurization tower is that the flue gas inlet velocity and temperature are 15 m/s and 393 K, respectively. Under these operating conditions, the pressure loss caused by the venturi accounted for 73.6% of the total pressure loss of the desulphurization tower. When the particle radius is between 0–150 μm, the particle size and the flue gas inlet velocity have the greatest influence on the particle residence time. Finally, the distribution of gas and particles before and after the adjustment of the desulphurization tower is compared, which showed that adjusting the bottom structure of the desulphurization tower could optimize the gas–solid flow.     

地下水人工补给过程中流速对多孔介质胶体堵塞的影响机理

通过一系列室内砂柱模拟实验,研究了流速对胶体在饱和多孔介质中滞留-迁移行为的影响;运用COMSOL软件模拟,拟合实验数据后得到表征胶体沉积的关键参数。结果表明：流速增大缩短了胶体在多孔介质中的滞留时间,并增强水动力拖拽力,导致介质对胶体的吸附量减少,有利于胶体的迁移;回灌时间的延续造成的多孔介质渗透系数降低,可通过瞬间增大流速使渗透系数在较短时间内恢复,然而随后形成新的吸附渗透性仍会降低。水源离子强度、介质粗糙度等因素会影响胶体迁移的流速效应。在相同条件下,吸附系数随着离子强度的增大而增加,随着流速的增大而增加。综合来看,离子强度的增加可抵消一部分水动力拖拽力的影响,提高胶体在多孔介质中滞留的概率;介质表面粗糙度的增加,可削弱水动力拖拽力作用,同时增加胶体与介质的吸附、沉积点位和接触面积,导致胶体易于在多孔介质中发生滞留并可能进一步导致介质堵塞。     

Migration and Deposition of Submicron Particles in Crossflow Microfiltration

Abstract

The migration and deposition of submicron particles in laminar crossflow microfiltration is simulated by integrating the Langevin equation. The effects of operating conditions on the particle trajectories are discussed. It is found that the Brownian motion of particles plays an important role in particle migration under a smaller crossflow velocity of suspension or a smaller filtration rate. Based on the simulated trajectories of particles, the transported flux of particles arriving at the membrane surface can be estimated. The particle flux increases with an increase of filtration rate and with a decrease of particle diameter; however, the effect of crossflow velocity on the particle flux is not obvious. The forces exerted on particles are analyzed to estimate the probability of particle deposition on the membrane surface. The probability of particle deposition increases with an increase of filtration rate, with a decrease of crossflow velocity, with a decrease of particle diameter, or with an increase of zeta potential on the particle surfaces. The simulated results of packing structures of particles on the membrane surface at the initial stage of filtration show that a looser packing can be found under a larger crossflow velocity, a smaller filtration rate, or a smaller diameter of filtered particles. Crossflow micro-filtration experiments are carried out to demonstrate the reliability of the proposed theory. The deviation between the predicted and experimental data of filtration rate at the initial period of filtration is less than 10% when the Reynolds number of the suspension flow ranges from 100 to 500.     

Rushton涡轮搅拌槽内流场特性及颗粒运动行为数值模拟

基于计算流体动力学（CFD）方法,采用大涡模拟（LES）和拉格朗日颗粒追踪技术计算了Rushton涡轮搅拌槽内流场特性及三种St颗粒的运动行为。平均流场（切向速度、轴向速度和径向速度）、颗粒速度及浓度分布方面与实验值的吻合度较好,验证了数值模拟的可靠性。结果表明,搅拌流场及颗粒运动均呈现循环流特性,当转速N=313r/min不变时,St=0.24的小颗粒几乎实现了均匀分布;而St=37.3的大颗粒与流体的跟随性较差,底部沉积率较高,容器顶部会出现一定的颗粒空白区。叶轮附近产生一系列的湍流涡结构,并且由于剧烈的颗粒-壁面碰撞,该位置颗粒拟温度最高;小颗粒（St=0.24）的运移主要受叶片后方尾涡的控制,均匀分布在低涡量区;而大颗粒（St=37.3）由于具有较大的惯性,运动不再由涡主导,很快被叶轮甩向边壁,穿过了尾涡所形成的高涡量区,故而叶轮对附近大颗粒的搅拌效果较差。     

Flow of nanodispersed catalyst particles through porous media: Effect of permeability and temperature

The proposed in situ catalytic upgrading of heavy oil to achieve an environmentally sustainable method for heavy oil recovery requires the placement of nanodispersed catalyst particles deep into the formation where it can accelerate the high‐temperature upgrading reactions. In continuation of the previous work [Zamani et al., Energy Fuels 24, 4980‐4988 (2010)], this paper presents results of several new experiments carried out to examine the effects of other parameters, including the connate brine salinity, absolute permeability, sand‐bed temperature and particle concentration on the propagation of nanoparticles in porous media. The results show that lower permeability, increased operating temperature and higher particle concentration did not significantly affect the propagation of nanodispersed catalyst suspension through the sand‐bed. Virtually the same filtration behaviour, displaying a rapid increase of effluent concentration at 1 pore volume injected to a steady concentration close to the inlet concentration was seen in all experiments. A classical phenomenological approach was used to model the macroscopic propagation behaviour of suspended particles in the porous medium. The model was successful in history matching the effluent composition profile observed in the experiments and the deposition profile obtained from post‐test analysis of the sand‐bed. © 2011 Canadian Society for Chemical Engineering