Velocity and concentration fields in settling tank of non-interacting solid particles

Summary In this paper there is a synthetic presentation of the theoretical principles of the phase difference method for the simultaneous measurements of size, velocity and concentration of particles dispersed in fluid, its application to spherical glass particles free falling in water at rest, and the measured velocity and concentration fields of the particles in a settling tank model. Particles with diameter between 75÷150 m were used. The method used seems reliable in obtaining the necessary information to analyze the performance of settling tanks in relation to the influencing factors the particles settling.

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Sommario In questo articolo sono presentati in forma sintetica i principi teorici del metodo della differenza di fase per la misura simultanea di velocità, dimensione e concentrazione di particelle disperse in un fluido, ed un'applicazione di tale metodo al caso di particelle di vetro, di dimensioni fra i 75–150 m, disperse in acqua. Le misure effettuate sono relative alla sedimentazione di particelle in acqua in quiete ed ai campi di velocità e concentrazione delle particelle che si realizzano in un modello fisico di vasca di sedimentazione rettangolare. I risultati ottenuti sembrano confermare l'adeguatezza del metodo impiegato per analizzare l'efficienza delle vasche di sedimentazione in relazione ai fattori che influenzano la sedimentazione di particelle.

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This work was supported by the Italian Ministry of Education.     

Dependence of the stagnation temperature of a jet of gas containing solid particles on the concentration of particles and their velocity

This article gives the results of experiments on the measurement of the stagnation temperature of a two-phase jet, issuing from a nozzle. The experiments were made using a mixture of air and aluminum oxide (particle diameter 50) with a ratio of the mass flow rate of the solid phase to the mass flow rate of the gas equal to 0.3–2.5, and at initial temperatures of the mixture of 150–450°C. It follows from the results of the experiments that the stagnation temperature of a two-phase flow considerably exceeds the temperature of the mixture at the inlet of the nozzle.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 175–176, July–August, 1970.     

Explosive dispersal of solid particles

Abstract. The rapid dispersal of inert solid particles due to the detonation of a heterogeneous explosive, consisting of a packed bed of steel beads saturated with a liquid explosive, has been investigated experimentally and numerically. Detonation of the spherical charge generates a blast wave followed by a complex supersonic gas-solid flow in which, in some cases, the beads catch up to and penetrate the leading shock front. The interplay between the particle dynamics and the blast wave propagation was investigated experimentally as a function of the particle size (100–925 m) and charge diameter (8.9–21.2 cm) with flash X-ray radiography and blast wave instrumentation. The flow topology during the dispersal process ranges from a dense granular flow to a dilute gas-solid flow. Difficulties in the modeling of the high-speed gas-solid flow are discussed, and a heuristic model for the equation of state for the solid flow is developed. This model is incorporated into the Eulerian two-phase fluid model of Baer and Nunziato (1986) and simulations are carried out. The results of this investigation indicate that the crossing of the particles through the shock front strongly depends on the charge geometry, the charge size and the material density of the particles. Moreover, there exists a particle size limit below which the particles cannot penetrate the shock for the range of charge sizes considered. Above this limit, the distance required for the particles to overtake the shock is not very sensitive to the particle size but remains sensitive to the particle material density. Overall, excellent agreement was observed between the experimental and computational results. Received 16 August 1999 / Accepted 26 June 2000     

Contact laws between solid particles

This paper presents a comprehensive study for the contact laws between solid particles taking into account the effects of plasticity, strain hardening and very large deformation. The study takes advantage of the development of a so-called material point method (MPM) which requires neither remeshing for large deformation problems, nor iterative schemes to satisfy the contact boundary conditions. The numerical results show that the contact law is sensitive to impact velocity and material properties. The contact laws currently used in the discrete element simulations often ignore these factors and are therefore over-simplistic. For spherical particles made of elastic perfectly plastic material, the study shows that the contact law can be fully determined by knowing the relative impact velocity and the ratio between the effective elastic modulus and yield stress. For particles with strain hardening, the study shows that it is difficult to develop an analytical contact law. The same difficulty exists when dealing with particles of irregular shapes or made of heterogeneous materials. The problem can be overcome by using numerical contact laws which can be easily obtained using the material point method.     

非金属固体材料在微重力环境中的着火及燃烧特性研究

微重力条件下固体材料的着火和火焰传播特性研究对于发展燃烧理论、保障航天器防火安全具有重要意义.由于地面设施微重力时间长度的限制,已有对微重力下材料燃烧过程的实验研究主要集中在热薄材料,而关于热厚材料的实验结果十分有限.作为实践十号(SJ-10)卫星科学实验项目之一,非金属材料燃烧实验将利用长时间微重力条件开展低速流动中典型热厚材料着火和火焰传播过程研究.简要介绍非金属材料燃烧项目的研究目标、空间实验内容、有效载荷技术特点和地面实验验证情况.     

Selection of working fluids for electrohydrodynamic experiments in terrestrial conditions and microgravity

Electrohydrodyamic (EHD) heat transfer enhancement and flow control methods are becoming increasingly popular in engineering science and applications both in terrestrial and low gravity applications. The correct choice of the working fluid is essential for the design and performance of EHD hardware and can pose challenge because some working fluids with favorable EHD properties can be unstable or hazardous. In this paper key properties and criteria for the selection of working fluids for single-phase (liquid) as well as gas–liquid and vapor–liquid two-phase electrohydrodynamic experiments and applications are discussed. Key physical and electrical properties as well as environmental and safety issues are reviewed for the sample fluids PF-5052, FC-72, R141b, cyclohexane and pure water. Microgravity experiments impose additional demands on the selection of the working fluids. Some of these demands are addressed by contrasting bubble dimensions and shapes at detachment, estimated using a simple thermodynamic model, in terrestrial and microgravity conditions with and without electric fields. Data are obtained using a simplified analytical model and verified experimentally.     

Geometry of the melting interface in cylindrical metal rods under microgravity conditions

The melting interface geometries present within cylindrical iron rods in microgravity are examined. Melting samples are quenched in microgravity by immersion in a water bath. Samples are sectioned on multiple planes and photo microscopy analysis is used to determine the shape of the melting interface on each plane. Images from multiple cross-sections are assembled to produce a three-dimensional representation of the melting interface present in microgravity. Iron rods are shown to have an asymmetric, convex melting interface in microgravity, with a significantly different (increased) heat transfer area compared to the planar normal-gravity case. The change in surface area of the melting interface between normal gravity and microgravity is shown to provide excellent agreement with the observed change in melting rate, as predicted by simple one-dimensional heat transfer analysis. To cite this article: N.R. Ward, T.A. Steinberg, C. R. Mecanique 335 (2007).     

Suspension of solid particles in a newtonian fluid

We consider the motion of a Newtonian fluid containing solid particles in the case of high concentration (the partial volume of solid is comparable to that of fluid) by using a homogeniztion technique associated with the small parameter ? (the ratio of the particle length to the characteristic macroscopical length). The limit behaviour as ? → 0 is that of fluid with anisotropy properties associated with a microstructure. The evolution equations for the limit flow and for the microstructure are given.     

Motion of solid particles in an oscillating liquid

The problem of motion of two “free” solid particles in a uniformly oscillating liquid is formulated and solved. In particular, it is found that the particles are capable of performing (side by side with oscillations) an average, monotonous displacement in the liquid as a whole.     

Dynamics of large solid particles in bioconvective sedimentation

Settling of one or two large solid particles in a bioconvection flow induced by gyrotactic motile microorganisms is investigated using a 2D numerical model. The results of varying the initial positions of large particles on the bioconvection flow pattern are investigated. The Chimera method is utilized to generate subgrids around the moving particles. It is demonstrated that the introduction of a single large particle displaces bioconvection plume and changes its shape. The introduction of two particles on the same side of the bioconvection plume further displaces the plume while the introduction of two particles on opposite sides reduces this displacement. The influence of the bioconvection plume on the particles' settling paths and particles' settling velocities is investigated. Copyright © 2006 John Wiley & Sons, Ltd.     

Fluidization of a bed of solid particles

As is known, fluidization of a bed of solid particles by liquid or gas filtration takes place for certain critical values of the parameters of the filtration regime. The determination of these critical values and the nature of the transition is of interest in connection with the development of fluidization technology in many branches of industry, and also in connection with certain other questions, among which we note the problem of the suspension of a sand plug in an oil well.The two-dimensional fluidization problem has been examined previously [1] as the problem of the limiting equilibrium of a medium which cannot withstand arbitrarily small tensile stresses. This model describes well the behavior of many types of bulk media encountered in practice. However, many cases lie beyond the limits of this model because of the presence of bonding forces between the particles. Bonding may be due to the adhesive forces which arise during the fluidization of fine powders [2, 3], and/or to magnetic and electrostatic forces [3, 4]. Another example is the agglomeration of particles during gas fluidization when small amounts of liquid are injected [5]; still another is the case in which sand particles are surrounded by thin films of oil when a sand plug is suspended in an oil well.In the present paper an extension of the results obtained in [1] is used to examine fluidization of a bed with account taken of the bonding forces between the particles. The two- and three-dimensional problems are studied.     

Characteristics of developing vertical bubbly flow under normal and microgravity conditions

The axial development of the void fraction profile, interfacial area concentration and Sauter mean bubble diameter of adiabatic nitrogen-water bubbly flows in a 9 mm-diameter pipe were measured using stereo image processing under normal and microgravity conditions. The flow measurements were performed at four axial locations (axial distance from the inlet, z normalized by the pipe diameter, D, z/D = 5, 20, 40 and 60) and with various flows: superficial gas velocity of 0.00840-0.0298 m/s, and superficial liquid velocity of 0.138-0.914 m/s. The effect of gravity on radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail based on the obtained database and visual observation. Following Serizawa-Kataoka’s phase distribution pattern criteria under normal gravity conditions, the phase distribution pattern map was developed. Similar to normal gravity two-phase flows, wall, core and intermediate void peak patterns are observed under microgravity conditions but a transition void distribution pattern is not observed in the current experimental conditions. The data obtained in the current experiment are expected to contribute to the benchmarking of CFD simulation of phase distribution pattern and interfacial area concentration in forced convective pipe flow under microgravity conditions.     

Propagation of waves in a suspension of solid particles

A theory is developed for the propagation of waves in a suspension of elastic or rigid solid particles in a viscous or inviscid compressible fluid, using a homogenization process. We study the case where the characteristic length of the particles is small compared with the wave length. In the case of a viscous fluid, a law similar to Darcy's law for the average velocity of the suspension is established, and in the case of macroscopic homogeneity and isotropy, the propagation of a plane wave displays one dilatational, damped and dispersive wave. In the case of a barotropic inviscid fluid, the average acceleration of the suspension depends, in a linear way, on the mean pressure gradient and in the case of macroscopic homogeneity and isotropy, the propagation of a plane wave displays one dilatational, undamped and non dispersive wave.     

Pipe flow with solid particles fixed in space

A group of solid particles were hung by slender rods in a pipe to make a model of two-phase flow of coarse particles. Pressure gradient and velocities were measured for different types of the models. The drag on the particles (spheres) were obtained from measurements of pressure gradient with some assumptions. The results are summarized as follows. (1) Mean velocities of fluid are lower in the central part of the pipe than in the circumferential part. Turbulence is remarkably increased by particles. The spectrum distribution of turbulent velocity becomes flatter. These results are similar to the gas-solid flow of coarse particles in a vertical pipe. (2) At a large Reynolds number, the drag coefficient per one sphere in the group is larger than that of a single isolated sphere in a uniform flow. When the spheres are arranged along the same line in the longitudinal direction, the drag coefficient becomes smaller as the longitudinal distance between the spheres is shortened.     

Settling motion of interacting solid particles in the vicinity of a plane solid boundary

The sedimentation of $N?1$ small arbitrarily-shaped solid bodies near a solid plane is addressed by discarding inertial effects and using 6N boundary-integral equations. Numerical results for 2 or 3 identical spheres reveal that combined wall–particle and particle–particle interactions deeply depend on the cluster's geometry and distance to the wall and may even cancel for a sphere which then moves as it were isolated. To cite this article: A. Sellier, C. R. Mecanique 333 (2005).     

Clustering behavior of solid particles in two-dimensional liquid-solid fluidized-beds

In this paper, the clustering behavior of solid particles in a two-dimensional （2D） liquid-solid fluidized-bed was studied by using the charge coupled devices （CCD） imaging measuring and processing technique and was characterized by fractal analysis. CCD images show that the distribution of solid particles in the 2D liquid-solid fluidised-bed is not uniform and self-organization behavior of solid particles was observed under the present experimental conditions. The solid particles move up in the 2D fluidized-bed in groups or clusters whose configurations are often in the form of horizontal strands. The box fractal dimension of the cluster images in the 2D liquid-solid fluidized-bed increases with the rising of solid holdup and reduces with the increment of solid particle diameter and superficial liquid velocity. At given solid holdup and solid particle size, the lighter particles show smaller fractal dimensions.