Flow Of Solid Particles Research Articles

Mechanics of advection of suspended particles in turbulent flow

In this paper, we explore the mechanics and the turbulent structure of two-phase (fluid–solid particle) flow system, for the first time, by considering the dynamic equilibrium coupled with suspended solid particle concentration, fluid flow and energetics of the two-phase flow system. The continuity, momentum and turbulent kinetic energy (TKE) equations of the fluid and the solid phases are treated separately to derive a generalized relationship of the two-phase flow system aided by suitable closure relationships. The results obtained from the numerical solution of resulting equations show that the particle concentration and the TKE diminish with an increase in the Rouse number, while the horizontal velocity component increases. On the other hand, the TKE flux, diffusion and production rates increase with an increase in the Rouse number, while the TKE dissipation rate decreases. In the vicinity of the reference level (that is, the hypothetical level from which the particles come in suspension), the Kolmogorov number increases with an increase in the Rouse number. However, as the vertical distance increases, this behaviour becomes reverse. A close observation of the turbulent length scales reveals that the Prandtl's mixing length decreases with an increase in the Rouse number, but the Taylor microscale and the Kolmogorov length scale increase.

Modeling of solid–gas flow fields via a correlation study

A correlation study for modeling of solid–gas flow fields is presented with an emphasis to the extents of single phase gas flow through stationary vertical packed beds of solid particles and dilute phase flow of suspended solid particles in horizontal channels. The experimental data in terms of local static pressure gradients dP/dx in flow direction are processed. The referred test cases are (i) horizontal air flow with fully suspended fine solid particles of the size range 75.5μm≤dp≤275μm for the magnitudes of superficial air velocity; U»minimum fluidization velocity; Umf, (ii ) air flow through a vertical fixed packed bed of solid particles with dp=6000μm for U«Umf. The visual observations at U=Umf through the vertical beds of solid particles with dp range; 150μm≤dp≤2750μm are also referred.A non-dimensional mode parameter P* is defined using well-known permeability parameter Pf, mixture density ρm and a time parameter t* as an original contribution. The proposed relationships of P* with air flow Froude Number, Fr and solid particle Froude number Frs determine the limits of the flow fields. The magnitude of P* is 1150 for stationary packed solid particles with Fr≤2. Meanwhile P*≤2 corresponds to the dilute phase flow of solid particles in air for Frs≤60. The proposed equations can also be used for the determination of solids velocity Us, U and Umf in the cited limits of Frs, Fr with an acceptable error margin of <±24%.

DEM/CFD approach for modeling granular flow in the revolving static mixer

DEM/CFD (Discrete Element Method/Computational Fluid Dynamic) approach was used to develop a three dimensional model of fluid flow and mixing process of solid particles within the revolving static mixer, type Komax. Static mixers are widely used in process industry, food industry, pharmaceutical and chemical industry. Mixing process adds significant value to the final product and it can be regarded as a key process. The quality and the price of the product often depend on mixing efficiency. Both design and operation of the mixing unit itself have a strong influence on the quality produced. In this paper, DEM is used for modeling granular flow of zeolite spheres in the revolving Komax static mixer and CFD method was used for modeling fluid flow through the Eulerian multiphase model. Coupling of these two methods provides reliable analysis of particle motion and flow pattern of the working fluid. The objective of this paper is to predict the behavior of particles after several rotations of the revolving static mixer. This type of device is used for premixing action before the main mixing process, for significant reduction of mixing time and energy consumption. This type of premixing action is not investigated in detail in the open literature. The results of the numerical simulation are compared with appropriate experimental results. The special design revolving static mixer, made of transparent Plexiglas was used for this experiment. Mixing quality was examined by RSD (relative standard deviation) criterion. Application of this model provides the optimization of the number of revolutions and geometrical parameters of mixing process taking into account the quality of the mixing process.

Application of nuclear techniques in two-phase liquid-solid particles hydrotransport investigations

The paper presents gamma radiation application to two-phase flow investigation in a vertical pipeline, where the flow of solid particles transported by water was examined by use of both: radiotracers and gamma-absorption method. The simultaneous use of two methods allows analyzing of important parameters of solid particles hydrotransport. In the described experiments as solid phase the ceramic models representing natural polymetallic ocean nodules were used. Radiotracers allow to track the movements of selected models, representing specified grain size and the designation of its velocity. However gamma-absorption method enables measurement of average solid-phase velocity. For analysis of electrical signals obtained from scintillation detectors the cross-correlation method has been applied.

Experimental study on the effects of big particles physical characteristics on the hydraulic transport inside a horizontal pipe

This paper presents an experimental study of the physical characteristic effects of large particles on hydraulic transport in a horizontal pipe. The particles are spherical and are large with respect to the diameter of the pipe (8%, 10%, 16% and 25%). Experiments were done to test the important parameters in solid transport (pressure, velocity, etc.). As a result, the relationship between the pressure gradient forces and the mixture velocity was substantially different from the pure liquid flow. However, in a single-phase flow a monotonous behavior of the pressure drop curve is observed, and the curve of the solid particle flow attains its minimum at the critical velocity. The regimes are characterized with differential pressure measurements and visualizations.

Placer-forming flows and mudflows as viscous fluids in river valleys

The paper is concerned with geologic processes in river valleys, such as the movement of alluvial placers and mudflows, regarded as viscous fluids. The dynamics of distribution of the placer mineral and mud-and-gravel material in a river valley was studied by modeling. Moving material was examined as an independent flow of solid particles (solid flow), free of the enclosing rocks. The flow-environment interaction was specified by mass forces, friction forces, and substance sources (drains). For the mathematical description of a solid flow, a set of viscous-liquid equations was used. The placer and mudflow parameters obtained during the numerical experiments agree satisfactorily with the full-scale data for real objects.

Numerical simulation of turbulent pulp flow of concentrated suspensions: Influence of the non-Newtonian properties of the pulp

ABSTRACTComputational tools such as Computational Fluid Dynamics can be useful to predict the flow of pulp suspensions. The present study aims to simulate numerically the flow of concentrated pulp suspensions using CFD tools. A commercial CFD software was used, Ansys Fluent, to simulate the turbulent flow of Eucalyptus and Pine suspensions. A pseudo-homogenous approach was followed by considering the pulp viscosity as a function of shear rate and pulp consistency. The model takes into account the existence of a very thin layer surrounding the core region, near the pipe wall. It is studied the influence of the presence of fibers in the lubrication layer, by considering that the pulp consistency depends on the distance to the pipe wall. Two low-Reynolds number (LRN) k-ϵ turbulence models, Abe-Kondoh-Nagano and Chang-Hsieh-Chen, implemented in Ansys Fluent by using User-Defined-Functions, were studied. The drag reduction effect observed experimentally could be reproduced by both models. The LRN models were modified taking into account the modifications proposed in literature for the turbulent flow of polymers and solid particles when a drag reduction effect is present. The models were validated by comparing the calculated pressure drop with the experimental values.

Experimental investigation of solid particles flow in a conical spouted bed using radioactive particle tracking

Solid particles flow in a conical spouted bed is characterized by radioactive particle tracking. The influence of operating conditions on key parameters of this flow is evaluated and discussed: the morphology of the solid bed is not strongly influenced by the forces exerted by the gas on the solid particles, but rather by geometrical considerations; the particles spend approximately 8% of their time in the spout in all experiments; it is the force exerted on the solid particles by the gas that directly controls the volumetric flow rate between adjacent regions, and not the amount of particles in the bed; as U/Ums increases, the volume of solid particles in the annulus decreases, the volume of solid particles in the fountain increases and the volume of solid particles in the spout remains constant. Correlations to predict key flow parameters as functions of operating conditions are also established and discussed. © 2015 American Institute of Chemical Engineers AIChE J, 62: 26–37, 2016

Projection methods for two velocity–two pressure models for flows of heterogeneous mixtures

In this paper, a numerical analysis of two velocity–two pressure models for flows of solid particles and fluids is presented. First, a formal exploitation of the weak formulation of such models asserts that they are amenable to integration via projection methods. The challenging issues in the algorithm development for these models are then documented and suitable numerical methodologies for their remedy are devised. Subsequently, an algorithm for the integration of the models of interest is proposed. This is a two-phase projection method on collocated grids that utilizes a fractional-step time-marching scheme. It is further endowed with an interface detection-and-treatment methodology to properly account for the stiffness induced by the presence of moving and deforming material interfaces. The efficiency and robustness of the proposed numerical method are assessed in a series of numerical experiments that are delineated in the last part of this paper.

Solid Particle Flow Battery Design and Characterization

Classic flow battery systems have consisted of transition metals dissolved in aqueous solvents which provide the electroactive materials. These flow battery systems have relatively low energy densities due to the stability window of water limiting the operating voltage and the solubility of the transition metals limiting the practical capacity. Recently, a few research groups have explored flow batteries with solid particles as the electroactive materials, in an effort to increase the energy density of the catholyte and anolyte materials. Many of these reported systems have extremely high viscosities because of the high solid particle loadings in the electrolyte. These high viscosities will result in high energy demands for the pumping of the electroactive fluids. Our group has been working on flow battery systems that take advantage of the energy density advantages of solid particles, but with a goal of not having prohibitive parasitic energy losses from pumping these fluids through the flow battery system. This work will describe the design and characterization of a flow battery that operates at reasonable viscosities for a particle-laden electrolyte, and the observed coupling between electrochemical properties and rheological properties in a solid particle flow battery system.

Viscous flow simulation of geological bodies

The results of the numerical simulation of geological processes that differ by ten orders of magnitude in flow rate are presented. In one case, it is the gold placer dynamics in a river valley. In another case, it is the rapid movement of the ice-debris mudflow. In both cases, the moving material was considered as an independent flow of solid particles free from host rocks. In order to mathematically describe such a solid flow, a system of viscous compressible fluid flow equations is used. The comparison of the results of the numerical experiments with field data for the real placer and mudflow has shown their sufficient similarity.

Experimental study of bedforms obtained with floating particles in a pipe flow

AbstractWe investigate experimentally the formation of bedforms caused by the sustained flow of water and solid particles in a circular pipe ($\varnothing =30~\text{mm}$). The special feature of the tests carried out was the use of floating particles ($d=756~{\rm\mu}\text{m}$, ${\it\rho}_{s}=907~\text{kg}~\text{m}^{-3}$) whereas bedforms are usually studied with sedimental materials. A closed loop was used, so that the solid flux could be maintained for an infinite time. The finite size of the tube led to the saturation of the growth of the vortex ripples produced. For the set of parameters studied, the threshold of motion was obtained within a range of laminar to low turbulent flow. The saturated state was studied to characterise it for different flow rates and solid loads. The frequency, wavelength and propagating velocity of ripples were determined using different methodologies based on image analysis and pressure analysis. The frequency and propagating velocity show a clear linear dependence on the initial Shields number, while the wavelength seems to be constant in our experiments.

Application of the phase method in radioisotope measurements of the liquid - solid particles flow in the vertical pipeline

The paper presents idea and an application of the gamma-absorption method to a two-phase flow investigation in a vertical pipeline, where the flow of solid particles transported by water was examined by a set of two 241 Am radioactive sources and probes with NaI(Tl) scintillation crystals. In the described experiments as solid phase the ceramic models representing natural polymetallic ocean nodules were used. For advanced analysis of electrical signals obtained from detectors the phase of cross-spectral density function has been applied. Results of the average solid-phase velocity measurements were compared with one obtained by application of the classical cross-correlation. It was found that the combined uncertainties of the velocity of solid particles evaluation in the presented experiment did not exceed 0.6% in phase method and 3.2% in cross- correlation method.

Modelling of solid particle flow in moving bed of COREX melter/gasifier based on discrete element method

Solid particle flow patterns in the moving bed zone of a melter/gasifier were studied using discrete element method (DEM). Interparticle forces were calculated using the Hertz–Mindlin no slip contact model. The simulation results of the solid particle flow patterns agree well with the experimental results exhibited by tracer particles. The solid particle flow pattern and descending velocity were studied, as well as the effect of the discharge rate of solid particles in the raceway on solid particle flow pattern in the moving bed.Results show that the moving bed could be divided into four subdomains based on the velocity of solid particles. A stagnation zone with semielliptic geometry is formed at the central bottom of the moving bed during drainage of solid particles. Furthermore, the simulated results of compressive force among solid particles in the moving bed zone indicate that the deadman zone undergoes a high degree of compressive force, especially at the centre of the gasifier. This finding implies that more compressive force resistant solid material should be placed at the centre zone by manipulating solid particles fed into the melter/gasifier.

Velocity measurement of the liquid–solid flow in a vertical pipeline using gamma-ray absorption and weighted cross-correlation

Developing technology for the deep-sea mining of polymetallic nodules requires, theoretical analyses, simulation and numerous experimental studies. In this paper authors focused on nuclear methods adoption to velocity of solid phase measurement in an extremely hard and varying environment. Selected results of the experimental studies of two-phase liquid–solid particles flow in a vertical pipeline obtained by probing with photon beams are presented. With the use of the sealed 241Am isotopes emitting gamma radiation of 59.5keV, and the scintillation probes with NaI(TI) detectors, the average transport velocity for ceramic models representing natural polymetallic nodules were determined. In the paper for analysis of the signals coming from the probes, the cross correlation function (CCF) and its modifications consisting in the combination of the CCF with such procedures as the average square difference function (ASDF) and the average magnitude difference function (AMDF) were used. An example of measurement is presented and its resulting uncertainties determined. In described experiment the relative values of the combined uncertainty of solid particles average velocity estimation are equal to: 3.2% for the CCF, 3.0% for the CCF/AMDF and 2.8% for the CCF/ASDF.

Numerical analysis of particle flows within a double expansion

The effect of solid particles within flows having zones of recirculation is of interest in pulverised fuel distribution and combustion at burners. Previous modelling of a 1/4 scale test rig was performed by Giddings et al. (2004), and an instability was later identified within the domain. Subsequently the transient dynamics of the flow of air through a double expansion were investigated numerically and a recirculation zone was found to develop at one of the four corners of the expansion. In the work presented here the flow of solid particles through this double expansion is investigated using the commercial software ANSYS FLUENT R14.0. The Stress-Omega Reynolds Stress Model is used to model the gas phase turbulence and the Discrete Particle Model is used to model the solid particle flow. The dynamics of the flow are reported here for 10μm and 60μm particles and for mass loadings from 0 to 1kgparticles/kgair. The simulations show a distinct transition to a vortex shedding type instability with the addition of the discrete phase. Furthermore, for increasing mass loading and particle Stokes number the Coanda effect is reduced leading to two large recirculation zones in opposing corners of the domain. The characteristics of the flow field are in qualitative agreement with studies of particle flows in jet flows and shear layers. This work serves to highlight some of the challenges in modelling complex pneumatic conveying flows from an industrial perspective.

Fluid lubrication effects on particle flow and transport in a channel

The study presented in this paper investigates the effects of fluid lubrication on solid particles flow and transport in slurries at high solids concentrations. Particle–particle and particle–wall collisions influence the behavior of slurries constrained between two parallel walls thereby affecting solids transport and the fluid flow field. As the concentration of the particles increases, collisions become more frequent compared to the dilute flow, and their effect on the flow field cannot be neglected. Particularly, lubrication from a thin fluid layer formed between approaching particles acts as non-linear damper affecting particle kinetic energy and post-collision behaviors. The Discrete Element Method coupled with Computational Fluid Dynamics (DEM–CFD), with a new user-defined contact model that accounts for particle lubrication and as implemented in the commercially available two-dimensional Particle Flow Code (PFC2D), was used to improve the understanding of the micro-mechanical behavior that contributes to particle clogging in a channel. It was found that the balance of fluid drag, related to the pressure drop in the channel and slurry properties such as fluid viscosity, particles volumetric concentration, particles size and channel size substantially contribute to the particle agglomeration even without considering gravity.

Modelling the Effect of Particle Size Distribution in Multiphase Flows with Computational Fluid Dynamics and Physical Erosion Experiments

It is known that particle size has an influence in determining the erosion rate, and hence equipment life, on a target material in single phase flows (i.e. flow of solid particles in liquid only or gas only flows). In reality single phase flow is rarely the case for field applications in the oil and gas industry. Field cases are typically multiphase in nature, with volumetric combinations of gas, liquid and sand. Erosion predictions of multiphase flows extrapolated from single phase flow results may be overly conservative. Current understanding of particle size distribution on material erosion in multiphase flows is limited. This work examines the effect of particle size distribution on material erosion of a cylindrical aluminium rod positioned in a 2" vertical pipe under slug and distributed bubble regimes using various water and air volume ratios. This is achieved through physical erosion experiments and computational fluid dynamics (CFD) simulations tailored to account for particle dynamics in multiphase flows.

Characterization of fluidization regime in circulating fluidized bed reactor with high solid particle concentration using computational fluid dynamics

The hydrodynamics inside a high solid particle concentration circulating fluidized bed reactor was investigated using computational fluid dynamics simulation. Compared to a low solid particle reactor, all the conventional fluidization regimes were observed. In addition, two unconventional fluidization regimes, circulating-turbulent and dense suspension bypassing regimes, were found with only primary gas injection. The circulating-turbulent fluidization regime showed uniformly dense solid particle distribution in all the system directions, while the dense suspension bypassing fluidization regime exhibited the flow of solid particles at only one side system wall. Then, comprehensive fluidization regime clarification and mapping were evaluated using in-depth system parameters. In the circulating-turbulent fluidization regime, the total granular temperature was low compared to the adjacent fluidization regimes. In the dense suspension bypassing fluidization regime, the highest total granular temperature was obtained. The circulating-turbulent and dense suspension bypassing fluidization regimes are suitable for sorption and transportation applications, respectively.

An Investigation on the Gas-solid Interactions in Periodically Excited Plane Mixing Layer by Using Vortex-in-Cell

The gas-solid interactions in a periodically excited plane mixing layer were investigated by vortex-in-cell technique. Transverse periodic forcing was posed on the initial location of plane mixing layer. Under the transverse periodic forcing, well organized spanwise Kelvin-Helmholtz rolls were formed. Not only the flow properties but the characteristics of particle dispersion and statistical properties of flow are detailed studied. In this study, Stoke number which bases on forcing frequency is chosen to be order one. Present results show that: solid particles always are impelled to the boundaries of vortex structures by centrifugal force, even though they ever temporally exist in the interior of vortex structures during pairing process; furthermore, the existence of solid particles in flow could enhance the forcing effects that make vortices evolve in flow field with more coherence in space and time; thus, negative turbulent production, which often appears in the highly excited plane mixing layer, could be observed in the present simulation at low forcing level and with solid particles.