Numerical study of the motion behaviour of three-dimensional cubic particle in a thin drum

The motion of three-dimensional cubic particles in a thin rotating drum is simulated by the SIPHPM method. The drums with frictional or smooth front and rear walls, and the particles of cubic and spherical shapes, and different particle numbers are considered to study the effect of cubic particle shape, end-wall frictions and filling levels. Different flow patterns of cubic particles are observed, which are significantly dominated by the friction from the end-walls. The probability density function of velocity components, the flatness factors are used to analyze the motion behaviour of cubic particle. The Froude number, ensemble mean and time averaged particle velocities are also analyzed. A primary and secondary mode of driving from the end-wall frictions are indicated and the mechanisms on the influences of wall friction, particle shape and filling levels are fully explained.     

Sensitivity of numerical parameters on DEM predictions of sediment transport

The current work presents a sensitivity study of selected numerical parameters on the large-eddy simulation–discrete element method predictions of sediment transport in a unidirectional open turbulent channel. The sensitivity of the particle friction factor, restitution coefficient, and spring stiffness used in the soft sphere collision model is tested in the three regimes of sediment transport comprising of essentially no motion, bed load, and suspended load flow regimes. The simulations are run for 10?s using base values of the parameters of interest (reference calculation), then one parameter is changed at a time and the corresponding change in quantitative result is observed for the following 15?s where averaged results in the last 10?s are compared to the reference calculation. The sensitivity analysis shows that the underpredicted sediment transport in the suspended load regime can be bridged by moderately decreasing the friction factor of the particles from 0.6 to 0.25. The impact of the same change in bed load regime is not as significant. Both the coefficient of restitution and the particle stiffness show less significant to negligible impact as compared to the friction factor.     

Centrifugal atomization of stainless-steel rotating rods melted by a high-power LASER beam

316L grade stainless steel powders were produced by centrifugal atomization during the melting of a rotating rod heated by a high-power LASER beam. The feasibility has been demonstrated by atomizing a range of stainless steel rods. The atomization process has been observed via high-speed imaging and fragmentation regimes have been identified according to a literature review on the rotating electrode process (REP). Results were compared with literature data and an existing prediction model for such a process. High-speed observation can monitor the present process and it is shown that a solidified layer of metal is formed at the edge of the rod during the process inducing metal flake ejection due to the centrifugal stresses. Effects of incident LASER beam power density, ejection speed and oxygen content of the surrounding atmosphere on the particle size distribution and the sample surface have been studied and compared with literature data on classical REP atomizers. The study focuses on the production of irregular particles during the atomization process and highlights the influence of the oxygen content in the surrounding atmosphere on the fragmentation regime and the resulting particle size distribution.     

Theoretical study of a novel refrigeration compressor – Part II: Performance of a rotating discharge valve in the revolving vane (RV) compressor

A new refrigeration compressor, named ‘Revolving Vane (RV) compressor’, has been introduced in Part I of this paper series. For a first time in refrigeration compressors, a rotating discharge valve is employed in the RV compressor mainly due to the rotation of the entire cylinder. This paper presents a theoretical investigation on the dynamic behavior of a reed-type discharge valve undergoing rotatory motion, with the primary objective of elucidating the applicability of such valves in refrigeration compressors. Under the application of the Euler–Bernoulli beam theory, a mathematical model of the rotating valve is formulated and the transient response of the valve under centrifugal loads in addition to pressure forces is analyzed. Results have shown that under careful design considerations, the performance as well as the reliability of the rotating discharge valve can be enhanced as compared to a non-rotating valve that has been used in all refrigeration compressors currently.     

Prediction of powder particle size during centrifugal atomisation using a rotating disk

The centrifugal atomisation of metallic melts using a rotating disk is an important process for powder production and spray deposition. The theoretical prediction of powder particle size is desirable for the design of atomisers. In this paper, wave theory was applied to analyse the disintegration of metallic melts in the film disintegration regime during centrifugal atomisation using a rotating disk. A mathematical model was proposed to predict the spray parameters. The governing equation for the fastest-growing wave number was developed and solved numerically. The effect of the variation in film thickness during film extension was taken into account. Film length and powder particle size were calculated and compared with available experimental data in the literature, and a good agreement was achieved. The influence of the break-up parameter was studied, and it is shown that the break-up parameter is not sensitive to the predicted powder particle size. Both simulated results and experimental data showed that fine powders can be produced by increasing disk speed.     

Prediction of powder particle size during centrifugal atomisation using a rotating disk

The centrifugal atomisation of metallic melts using a rotating disk is an important process for powder production and spray deposition. The theoretical prediction of powder particle size is desirable for the design of atomisers. In this paper, wave theory was applied to analyse the disintegration of metallic melts in the film disintegration regime during centrifugal atomisation using a rotating disk. A mathematical model was proposed to predict the spray parameters. The governing equation for the fastest-growing wave number was developed and solved numerically. The effect of the variation in film thickness during film extension was taken into account. Film length and powder particle size were calculated and compared with available experimental data in the literature, and a good agreement was achieved. The influence of the break-up parameter was studied, and it is shown that the break-up parameter is not sensitive to the predicted powder particle size. Both simulated results and experimental data showed that fine powders can be produced by increasing disk speed.     

Influence of particle elasticity in shear testers

Two dimensional simulations of non-cohesive granular matter in a biaxial shear tester are discussed. The effect of particle elasticity on the mechanical behavior is investigated using two complementary distinct element methods (DEM): Soft particle molecular dynamics simulations (Particle Flow Code, PFC) for elastic particles and contact dynamics simulations (CD) for the limit of perfectly rigid particles. As soon as the system dilates to form shear bands, it relaxes the elastic strains so that one finds the same stresses for rigid respectively elastic particles in steady state flow. The principal stresses in steady state flow are determined. They are proportional to each other, giving rise to an effective macroscopic friction coefficient which is about 10% smaller than the microscopic friction coefficient between the grains.     

Radial patterns and velocity field of non-Brownian suspensions in a fully filled horizontal rotating cylinder

This work reports radial patterns and velocity profiles of fluid-particle suspensions rotating in a fully filled horizontal cylinder using the technique of Particle Image Velocimetry. Dilute and mono-dispersed suspensions of non-Brownian settling as well as floating particles were considered. An analysis of the effect of particle shape on the flow patterns is provided. This was carried out by comparing the suspensions of spherical and cylindrical particles. Impact of particle shape on the particle-fluid interaction in determining the flow structure is more pronounced at lower speeds. Analysis of the velocity profiles showed a resemblance of the buoyant and settling suspensions phases. Despite the similar features observed, a difference was noted when the centrifugal forces dominate. Our experimental results are in good qualitative agreement with the previous experiments and simulations. Through a detailed investigation of velocity field we have established the strong relationship between the phase transition and rotational speed.     

Order formation of colloidal nanoparticles adsorbed on a substrate with friction

We examine the adsorption process and order formation of colloidal nanoparticles on a planar surface with friction. We perform Brownian dynamics simulations with a three-dimensional cell model in which the particle–particle and particle–substrate interactions are modeled on the DLVO theory, and examine the effects of the friction acting between the adsorbed particles and the substrate on the adsorbed structure formed on the substrate. The results obtained are as follows: when the friction is so strong that the adsorbed particles are stuck to the substrate, ordered structures never form, which seems to be quite natural. However, when the magnitude of the frictional force is moderate, an ordered structure can form even with low coverage because the frictional force aids order formation. This is because the friction counterbalances the particles’ Brownian motion, which would otherwise disturb the ordered structure. Furthermore, through a detailed examination of the distribution of the Brownian motion, it is demonstrated that an increase in the friction has a similar effect as a decrease in temperature.     

Theory of centrifugal sedimentation of large particles

The motion of particles of finite size in rotating viscous liquids is investigated. On the basis of the properties of centrifugal sedimentation described, its possible technical applications are discussed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 5, pp. 865–869, May, 1977.     

Particle screening phenomena in an oblique multi-level tumbling reservoir: a numerical study using discrete element simulation

Due to their wide usage in industrial and technological processes, granular materials have captured great interest in recent research. The related studies are often based on numerical simulations and it is challenging to investigate computational phenomena of granular systems. Particle screening is an essential technology of particle separation in many industrial fields. This paper presents a numerical model for studying the particle screening process using the discrete element method that considers the motion of each particle individually. Dynamical quantities like particle positions, velocities and orientations are tracked at each time step of the simulation. The particular problem of interest is the separation of round shape particles of different sizes using a rotating tumbling vertical cylinder while the particulate material is continuously fed into its interior. This rotating cylinder can be designed as a uniform or stepped multi level obliqued vertical vessel and is considered as a big reservoir for the mixture of particulate material. The finer particles usually fall through the sieve openings while the oversized particles are rebounded and ejected through outlets located around the machine body. Particle–particle and particle–boundary collisions will appear under the tumbling motion of the rotating structure. A penalty method, which employs spring-damper models, will be applied to calculate the normal and frictional forces. As a result of collisions, the particles will dissipate kinetic energy due to the normal and frictional contact losses. The particle distribution, sifting rate of the separated particles and the efficiency of the segregation process have been studied. It is recognized that the screening phenomenon is very sensitive to the machines geometrical parameters, i.e. plate inclinations, shaft eccentricities and aperture sizes in the sieving plates at different levels of the structure. The rotational speed of the machine and the feeding rate of the particles flow have also a great influence on the transportation and segregation rates of the particles. In an attempt to better understand the mechanism of the particle transport between the different layers of the sifting system, different computational studies for achieving optimal operation have been performed.     

DEM analysis of powder deaggregation and discharge from the capsule of a carrier-based Dry Powder Inhaler

In carrier-based Dry Powder Inhalers (DPI), fine API powder covers the surface of bigger carrier particles giving rise to dry coated particles, such that their flow properties are improved. In the hard-shell capsule of Cyclohaler DPI, powder deaggregation and discharge occurs as a result of the centrifugal motion and the subsequent aerodispersion to the mouthpiece induced by the patient’s inhalation. In this work, the crucial initial transient of this dispersion process was analysed through DEM (Discrete Element Method) simulations, by considering the solid phase only. The accelerated rotational motion of the capsule was simulated in the frame of reference of an observer rotating with the capsule, appropriately considering fictitious forces. The effect of the vibrations due to collisions between the capsule and the inhaler on powder discharge was evaluated as well for carrier particle systems. The results provide a punctual mapping of the particle-wall collisions within the capsule, allowing the path of the solids to be tracked until discharge. Simulations were carried out on drug-carrier blends with extreme size difference, considering adhesive interactions, elucidating the early-stage dynamics of the detachment process that occurs inside the capsule due to the interactions between particles and between particles and walls.     

Transfer of discrete inclusions by fluxes with concentrated vorticity

Problems related to modeling of the motion of discrete inclusions (solid particles, drops or bubbles) in flows with concentrated vorticity are considered. A comparative evaluation of the force factors in the equation of motion of a test particle is made. The results of numerical modeling of the motion of discrete inclusions in the gap between concentric rotating cylinders and a vortex flow formed by the liquid rotating with a constant angular velocity over a fixed base are discussed. The coordinates of the points of equilibrium of the test particle in the vortex flow are found. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 2, pp. 36–45, March–April, 2007.     

Segregation pattern of binary-size mixtures in a double-walled rotating drum

Size-induced granular segregation was performed systematically and experimentally in an almost fully filled double-walled rotating drum at 10 different rotation speeds and two different side wall types. The motion of the granular materials was recorded using a high-speed camera for image analysis of particle segregation development in the drum. With continual tracking of the particle movements, the velocity, fluctuations, and granular temperatures were measured. The experimental results indicate that both rotation speeds and friction coefficient of side walls significantly affect segregation phenomena in binary-size mixture granular flows. The results demonstrate similar situations to the Brazil-nut effect and its reverse in the radial direction at either high or a low rotational speed (where the Froude number (Fr) is far from 1). At these instances, the maximum granular temperature occurs near the side walls. Specifically, a double segregation effect (DSE) is found at Froude number (Fr) close to 1. These results can be used in many industrial processes, for example, size grading of materials, screening of impurities, and different structures of functionally graded materials. Moreover, the maximum granular temperature occurs in the middle of the ring space. It causes small particles to move toward both side walls as it pushes bigger particles to accumulate in the middle of the ring space of rotating drum.     

A Novel Control Unit for a Friction Welding Machine Based on Computer

Typical friction welds are made by holding a non-rotating sample in contact with a rotating sample under constant or gradually increasing pressure until the interface reaches the welding temperature and then stopping pressure rotating to complete the weld. This process requires additional time and is labor intensive. Recently, several control systems have been introduced to the industry for improving the welding process such as conventional automatic control, microcontroller control, and Programmable Logic Controller (PLC). However, these processes have limitations either on materials selection or on visualization. In this study, continuous monitoring, control and recording are implemented. Computer-controlled platform for the simulation and control of mechanisms is based on a Microsoft Visual Basic environment. Welding parameters such as friction time, forge time and breaking time are entered with a keyboard and can be saved and used again. To show the feasibility and versatility of the study, the evaluation is used for sample joining. It has been observed that this system works successfully and gives good performance.     

Investigation of Fe2O3–Al and Cr2O3–Al reactions using a high speed video camera

Abstract

Self propagating high temperature synthesis is a simple, fast and energy efficient process with a wide range of applications, one of which is the coating of the internal surfaces of steel pipes using a centrifugal thermit process. The process involves a highly exothermic reaction between powder reactants distributed around a steel tube rotating at high speed. Although the process has been widely studied, important features, particularly how the reaction propagates, have not been completely revealed due to extremely high reaction rates and temperatures. In the present work, Fe₂O₃–Al and, to a lesser degree, Cr₂O₃–Al reactions were studied under stationary (non-rotating) and rotating conditions using a high speed video camera by which the centrifugal thermit process was, for the first time, recorded optically. Video recordings clearly demonstrate that, in contradiction to current belief, the reaction does not always propagate in a well ordered (spiral) pattern, but involves multiple, randomly distributed ignition sites.     

Characteristics and atomization behavior of Ti-6Al-4V powder produced by plasma rotating electrode process

In the present research, the characteristics and atomization behavior of Ti-6Al-4V powders produced by plasma rotating electrode process (PREP) with different rotation speeds were investigated. Three kinds of particles in the as-PREPed powders are observed: spherical particles, satellite particles and irregular particles. The mean particle size of the PREP powder decreases and its distribution becomes narrower gradually with increasing rotation speed. PREP powder at higher rotation speed demonstrates lower fractions of both satellite particles and irregular particles. By observing the residual electrode tip, it is considered that the irregular particles with corner or flat shape are possibly caused by the tearing of liquid film under the action of centrifugal force and shear force during the atomization process.     

Anomalies in multiple scattering of charged particles in a thick crystal

The dynamics of charged particle channeling in a crystal consisting of atomic chains is considered. The multiple scattering of charged particles, introduced by the trajectory integral method, leads to transitions between dynamical modes of the axial channeling, whereby double channeling is a sink for the normal channeling. Volume rechanneling takes place under the conditions of random motion. In this case, up to ∼20% of incident charged particles move in the channeling regime over a depth equal to the normal range, and a considerable fraction of these particles are involved in the double channeling regime.     

Compressive and tribological properties of Al2O3 fibre and hexagonal BN particle hybrid reinforced Al-Si alloys

Al₂O₃ fibre-hexagonal BN particle hybrid reinforced aluminium-silicon alloys were fabricated by centrifugal force infiltration route. Hardness test and ultimate compressive test results are reported. The wear and friction properties of hybrid MMCs was investigated by means of a block-on-ring (bearing steel) type wear rig in a dry sliding condition. It is shown that the hardness and ultimate compressive strength of hybrid MMCs was evidently decreased with the addition of hexagonal BN particles, however, the wear rate and coefficient of friction of hybrid MMCs was improved simultaneously with increase of BN particle volume fraction, especially for the higher applied loads in the test.