Wet granular materials in sheared flows

The transport properties of wet granular materials in a shear cell apparatus have been studied. If the particles are wet, the flow becomes more viscous forming liquid bridges between particles. The dynamic liquid bridge forces are considered as the cohesive forces between particles to restrict their movements. The cohesive forces make the particles stick tighter with each other and hamper the movement of particles. The mixing and transport properties are influenced seriously by the amount of moisture added in the flow. This paper discusses a series of experiments performed in a shear cell device with five different moisture contents using 3-mm glass spheres as the granular materials. The motion of granular materials was recorded by a high-speed camera. Using the image processing technology and particle tracking method, the average and fluctuation velocities in the streamwise and transverse directions could be measured. The self-diffusion coefficient could be found from the history of the particle displacements. The self-diffusion coefficients and fluctuations in the streamwise direction were much larger than those in the transverse direction. Three bi-directional stress gages were installed to the upper wall to measure the normal and shear stresses of the granular materials along the upper wall. For wetter granular material flows, the fluctuation velocities and the self-diffusion coefficients were smaller.     

The effect of liquid viscosity on sheared granular flows

This work investigates the effect of transport properties in sheared granular flows with adding different silicone oils. We performed a series of experiments in a shear cell device using 2-mm soda lime beads as the granular materials by adding little amount of different silicone oils. The viscosity of silicone oils added was changed in different tests. By particle tracking method, the velocities, the velocity fluctuations and the self-diffusion coefficients were measured and analyzed. It was found that for the granular system with adding the more viscous silicone oil, the system became less active due to the greater shear force and cohesive force, which resulted in the decrease of velocity fluctuations and diffusions. Three bi-directional stress gages were installed to the upper wall to measure the normal and shear stresses of the granular materials along the upper wall. Thus, the effective viscosities of the wet granular material systems could be evaluated. The dimensionless normal and shear stresses, and the effective viscosity in the wet sheared granular flow were found to decrease with the increase of the viscosity of the added silicone oil. The influence of the viscosity of added fluid on these transport properties of wet granular systems will be discussed.     

Transport property measurements in sheared granular flows

Experiments were performed in a shear cell device under four different solid fractions. The glass spheres with a mean diameter of 3 mm were used as granular materials. The motions of the granular materials were recorded by a high-speed camera. By using image processing technology and a particle tracking method, the average and fluctuation velocities in the streamwise and the transverse directions could be successfully measured and analyzed. Three bi-directional stress gages were used to measure the normal and shear stresses along the upper boundary. The effective viscosity of the granular material flow can be calculated. By tracking the movements of particles continually, the curves of the mean-square diffusive displacements versus time were plotted and were used to determine the self-diffusion coefficients from the slopes of the curves. The fluctuations and the self-diffusion coefficients in the streamwise direction were much higher than those in the transverse direction. The fluctuations were found to increase with the solid fraction, but the diffusion coefficients were greater in a more dilute flow system.     

Experimental analysis of dynamic properties in wet sheared granular matter

We performed experiments to measure the dynamic properties of wet granular matter in a shear cell device. The purpose was to quantify the effect of the liquid bridge force on granular systems. The motions of the granular materials were recorded by a high-speed camera. Image processing technology and particle tracking method were employed to measure the velocities, fluctuation velocities and granular temperatures in the streamwise and the transverse directions. The results show that adding small amounts of liquid with different viscosities, and changing the wall velocity, both have significant influences on the dynamic properties of wet granular matter due to the formation and rupturing of liquid bridges. The energy dissipation due to the formation and rupturing of the liquid bridges increases with the increase of wall velocity and the increase of liquid viscosity. The effect of the liquid bridge force on the dynamic properties is not only dependent on the liquid viscosity but also on the kinetic energy of the granular system.     

Influence of molecular composition on the development of microstructure from sheared polyethylene melts: Molecular and lamellar templating

A combination of in situ and ex situ X-ray scattering techniques and transmission electron microscopy has been used to study the crystallization behaviour of polyethylene, following the imposition of melt shear. In the case of a branched material, the imposition of shear flow up to a rate of 30 s⁻¹ was found to induce no anisotropy. Although shearing the linear material only ever induced a very small degree of anisotropy in the melt, for shear rates >0.15 s⁻¹, subsequent crystallization resulted in increasing anisotropy. Blends of the above two polyethylenes were produced, in which the linear material constituted the minority fraction (∼10%). Isothermal crystallization at temperatures where extensive crystallization of the branched material does not occur demonstrated that the behaviour of the linear component of the sheared blend mirrored that of the linear polyethylene alone. However, in addition, it was found that when crystallized in the presence of an oriented morphology, the branched polymer also formed anisotropic structures. We have termed the process templating, in which the crystallization behaviour of the bulk of the system (∼90% branched material) is completely altered (spherulitic to oriented lamellar) by mapping it onto a pre-existing minority structure (∼10% linear polymer).     

The maximum thickness of upper shear layers of granular materials in rotating cylinders

Published data from Henein et al. (Metallurgical Transactions 14B (1983a) 191-206), Woodle and Munro (Powder Technology 76 (1993) 241-245), Boateng and Barr (Journal of Fluid Mechanics 330 (1997) 233-249), Van Puyvelde et al. (Transactions of the Institute of Chemical Engineers 78A (2000) 643-650), and Felix et al. (Powder Technology 128 (2002) 314-319) on the maximum thickness of shear layers at the upper surface of a freely flowing granular material being rotated in a cylindrical drum are modeled and analyzed. A theory is developed which suggests that all distances should be scaled by x_m, or half the length of the shear layer, which should remove most of the explicit dependence on the filled fraction. The rolling regime is predicted to contain two extreme regimes. The dispersive (inertial) regime occurs when the parameter Fr_s(x_m/σ)^4/3 is small (large), and is characterized by the dominance of dispersive (inertial) effects. Here Fr_s is a particle-dependent Froude number scaled by x_m, and σ is the particle diameter. An author-dependent and particle-dependent parameter λ is introduced to account for the different definitions and particle types used. Regression analysis shows that most of the data sets above (for the rolling regime) are approximately described by the dispersive regime. Our theory predicts that shear layers in the rolling regime should be almost identical for fill fractions symmetric about the half-filled level. All of the data analyzed satisfy essentially the same scale-up relationship, and does not support the idea that the maximum shear layer thickness should be about ten particle diameters.     

管壳式换热器壳程高黏度流体的传热强化

传统的管壳式高黏度流体换热器采用光滑管设计制造,其壳程传热及流动效能低,壳程传热阻力占总热阻的80％以上,且流动阻力损失较大,提高壳程流体的传热膜系数和降低流动阻力是提高高黏度流体换热器效能的技术关键．     

A new model for simulating particle transport in a low‐viscosity fluid for fluid‐driven fracturing

Fluid‐driven fracture (i.e., Hydraulic fracturing) is an important way to stimulate the well productivity in the development of unconventional reservoirs. A low‐viscosity fluid called slickwater is widely used in the unconventional fracturing. It is a big challenge to simulate the particle (or proppant) transport in the low‐viscosity fluid in a field‐scale fracture. A new model to simulate particle transport in the low‐viscosity fluid in a field‐scale fracture is developed. First, a new parameter is defined, called the rate of proppant bed wash‐out, by which we incorporated the mechanism of proppant bed wash‐out into Eulerian‐Eulerian proppant transport model. Second, we proposed a novel way to consider the effect of proppant settling on the proppant concentration in the upper layer (or suspending layer) to accurately simulate the proppant transport. Additionally, a dimension reduction strategy was used to make the model quickly solved. Our simulation results were compared with published experimental data and they were consistent. After validation, the effect of fluid viscosity, injection rate, fracture height, and proppant concentration on the proppant distribution in a fracture is investigated. This study provides a new model to simulate particle transport. Meanwhile, it gives critical insights into understanding particle transport in the field‐scale fracture. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3542–3552, 2018     

Influence of interface energy of primary particles on the deformation and breakage behaviour of agglomerates sheared in a powder bed

In this paper, the parameters that affect the deformation and breakage of agglomerates embedded in a bed of particles subjected to rapid shearing are identified and analysed. The influences of interface energy between the primary particles and the size ratio (between agglomerates and particles of the bed) on the deformation characteristics of the agglomerate are addressed. The study is based on computer simulations using the distinct element method (DEM). It has recently been shown that for agglomerates having a size ratio greater than about 7, the nature of stresses experienced by the agglomerates when sheared inside a particulate bed is predominantly hydrostatic, hence it is difficult to break them (Hassanpour et al., 2007). However, the role of the interface energy between primary particles coupled with the effect of size ratio on the breakage and deformation characteristics of agglomerates during shearing has not been analysed. This feature is of great interest in the agglomeration process and is hence addressed in the present study. It is found that despite the predominantly hydrostatic nature of stresses responsible for retarding the breakage, agglomerates with size ratio greater than about 7 could undergo macroscopic deformation when the surface energy between the primary particles is decreased below a critical value. Furthermore, a failure map of agglomerates is presented in terms of their size ratio and the value of interface energy of the primary particles.     

Conduction and dissipation in the shearing flow of granular materials modeled as non-Newtonian fluids

After providing a brief review of the constitutive modeling of the stress tensor for granular materials using non-Newtonian fluid models, we study the flow between two horizontal flat plates. It is assumed that the granular media behaves as a non-Newtonian fluid (of the Reiner-Rivlin type); we use the constitutive relation derived by Rajagopal and Massoudi [Rajagopal, K. R. and M. Massoudi, “A Method for measuring material moduli of granular materials: flow in an orthogonal rheometer,” Topical Report, DOE/PETC/TR-90/3, 1990] which can predict the normal stress differences. The lower plate is fixed and heated, and the upper plate (which is at a lower temperature than the lower plate) is set into motion with a constant velocity. The steady fully developed flow and the heat transfer equations are made dimensionless and are solved numerically; the effects of different dimensionless numbers and viscous dissipation are discussed.     

Electrokinetic transport of water and methanol in Nafion membranes as observed by NMR spectroscopy

Electrophoretic NMR (eNMR) and pulsed-field-gradient NMR (PFG-NMR) methods were used to study transport processes in situ and in a chemically resolved manner in the electrolyte of an experimental direct methanol fuel cell (DMFC) setup, constituted of several layers of Nafion 117. The measurements were conducted at room temperature for membranes fully swollen by methanol-water mixtures over a wide concentration interval. The experimental setup and the experimental protocol for the eNMR experiments are discussed in detail. The magnitude of the water and methanol self-diffusion coefficients show a good agreement with previously published data while the ratio of the two self-diffusion coefficients may indicate an imperfect mixing of the two solvent molecules. On the molecular level, the drag of water and methanol molecules by protons is roughly of the same magnitude, with the drag of methanol molecules increasing with increasing methanol content. The electro-osmotic drag defined on mass-flow basis increased for methanol from a low level with increasing methanol concentration while that of water remained roughly constant.     

Mixing behaviors of wet granular materials in gas fluidized bed systems

The discrete element method combined with computational fluid dynamics was coupled with a capillary liquid bridge force model for computational studies of mixing behaviors in gas fluidized bed systems containing wet granular materials. Due to the presence of strong capillary liquid bridge forces between wet particles, relative motions between adjacent particles were hindered. There was a high tendency for wet particles to form large aggregates within which independent motions of individual particles were limited. This resulted in much lower mixing efficiencies in comparison with fluidization of dry particles. Capillary liquid bridge forces were on average stronger than both fluid drag forces and particle–particle collision forces and this accounted for the difficulty with which individual particles could be removed and transferred between aggregates. Such exchange of particles between aggregates was necessary for mixing to occur during fluidization of wet granular materials but required strong capillary liquid bridge forces to be overcome. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4058–4067, 2013     

焦耳热效应对毛细管电泳中样品区带传输的影响

毛细管区带电泳过程中产生焦耳热效应会改变溶液的黏度,进而改变样品区带到达检测窗口的时间。建立了一个包含电势分布方程、连续性方程、动量方程、能量方程和样品组分迁移扩散方程的数学模型,应用有限元数值模拟的方法,对这些耦合的方程进行了求解。计算结构分析了在考虑和不考虑焦耳热的情况下样品组分区带的传输过程。结果表明,毛细管内径、对流换热系数及缓冲溶液浓度都会影响样品区带在毛细管中的运动速度,进而改变其到达检测窗口的时间。     

Determination method of the cavern boundary viscosity in a stirred tank with pseudoplastic fluid

It is essential to predict the cavern boundary accurately for investigating the cavern characteristics and achieving efficient mixing of the pseudoplastic fluids. The distribution characteristics of apparent viscosity of xanthan gum solutions at different mass concentrations stirred by the impeller of perturbed six-bent-bladed turbine (6PBT impeller) were numerically investigated through the computational fluid dynamics (CFD) simulation based on laminar flow model. The determination method of the cavern boundary viscosity was presented, and the predicted results were compared with those of traditional velocity method. Results showed that the data of the power consumption predicted using CFD simulation agreed well with those measured by torque experiment, which validated the laminar flow model. The η_a − γ curve changes from nearly horizontal straight line to the power function curve along the direction of center axis toward tank wall. As a result, the location of the transitional point can be determined as the cavern boundary, and the corresponding viscosity is the cavern boundary viscosity. The ratio of the cavern boundary viscosity and the fluid yield viscosity ( η_a/η_y ) always remains approximately constant, that is, at different speeds. Compared with the traditional velocity method, the boundary viscosity method can maintain its high accuracy for exhibiting the cavern boundary, and the predicted cavern size and development are always in good agreement with the CFD results free from the speed and the impeller type. So this work can provide a new way for accurately characterizing the cavern boundary.     

烯烃平均碳数对聚-α烯烃合成油粘度指数和凝点的影响

将汽油烯烃、煤油烯烃及柴油烯烃以不同比例混合进行聚合实验 ,考察了烯烃的平均碳数分布对聚 -α烯烃合成油粘度指数和凝点的影响。     

宽黏度域轴流桨及在非牛顿流体中功率特性的实验研究

根据某反应的特定工艺过程要求,提出了一种适合宽黏度域的高效轴流式搅拌桨--SP304型轴流式搅拌桨,该桨叶片呈空间扭转状,且具有曲率,可减少流体阻力,提高排出性能.并设计了一套实验装置对这种高效轴流桨在非牛顿流体中的功率特性进行研究,得到了功率常数K_p、Metzner常数k_s和功率特性曲线,为工业化装置的设计提供实验数据.通过观察实验中不同浓度、不同转速下的流体流动细节,可以获得整个流动场的概念,对搅拌桨离低高度、桨间距等参数设计具有重要的指导意义.根据实验结果对此高效轴流搅拌桨成功地进行了工业应用.     

The development of circulation cell structures in granular materials undergoing compression

This paper predicts the formation of microstructures within a granular material undergoing biaxial compression. Using the discrete element method we have tested ensembles of particles of varying geometric shape and size. The tests predict that the motion of the particles deviates significantly from that predicted by continuum theory. The particles form localized coherent structures (here called circulation cells) in which groups of particles instantaneously behave as a rigid body. These circulation cells migrate and coalesce to form larger structures. Eventually a global shear band forms at the boundary of two or more of the circulation cells.     

Influence of carrier fluid on the electrokinetic and rheological properties of shear thickening fluids

This paper presents a study on the influence of hydroxyl groups and oxygen atoms together with chain length and branching of carrier fluid on the rheological and electrokinetic properties of shear thickening fluid (STF). An STF is non-Newtonian fluid behaviour in which the increase of viscosity increases with the applied shear rate. Ethylene glycol, triethylene glycol, 1,3-propanediol, glycerin, poly(propylene glycol) of different molecular weight and poly(propylene glycol) triol were used as the carrier fluids (dispersants). Silica powder with an average particle size of 100 nm was used as the solid phase. Zeta potential, particle size distribution (by DLS technique), steady-state and dynamic rheological measurements were conducted. Experimental results indicate that a different amount of hydroxyl groups and oxygen atoms together with chain length and branching of carrier fluids have a significant influence on the intermolecular interactions thereby and on the rheological properties of suspensions. Depending on the composition, it is possible to control rheological properties. The use of a suitable carrier fluid allows the required pattern flow to be obtained, from Newtonian through shear thinning to shear thickening, given specific shear conditions.     

超临界流体萃取固态物料数值模拟的研究进展

介绍了超临界流体萃取固态物料的数值模拟方法 ,对固体物料萃取的经验动力学模型、热质类比模型、质量守恒模型的原理及传质特性进行了评述