Vertical Motion Of Particles Research Articles

Evaluation of airlift pump performance for vertical conveying of coal particles

AbstractOne of the crucial aspects of reducing air consumption when conveying particles with an airlift pump is to know the factors that affect the process of particle motion at an initial velocity of zero. To determine the influence of submergence ratio and physical properties of particles (such as size, shape, and mass) on the onset of vertical particle motion, the airlift pump was taken as the research object, and spherical glass together with irregular shaped coal were used as experimental test particles. The results show that unlike the water-solid environment, the start of particle motion in the water-air mixture does not always occur at a certain value of superficial water velocity and this value also increases with increasing submergence level. Among the parameters considered, the role of submergence ratio is much more effective than the dimensions and the shape of the particle, because by increasing submergence from 0.3 to 0.8, it is possible to reduce air consumption by up to 8 times. Based on this study the corresponding theoretical model derived by Fujimoto et al. is optimized, wherein the overall agreement between the modified theory and present experimental data is particularly good. Contrary to Fujimoto, the minimum superficial water velocity for lifting solids in the air-water mixture is not always smaller than water ambient which indicates on optimum submergence ratio higher than 0.7. Finally, a new criterion was introduced to describe the moment of onset of the particle motion as a function of the superficial fluid velocity ratio for each submergence value.

Flow characteristics and packing structures of dense granular flow around an immersed cylindrical tube

We perform discrete element simulations to investigate the influence of the flow velocity, the particle size, and the particle-particle sliding friction on flow patterns and packing structures of dense granular flow around an immersed cylindrical tube. Results indicate that varying the flow velocity and particle radius does not obviously affect the scaled velocity field. However, increasing the velocity enhances the vertical motion of particles near the void space and increasing the particle size reduces the particle flowability in the horizontal direction. Both effects result in the enlargement of the void space below the tube. Moreover, larger particle friction leads to a looser packing structure and a larger void region. The width and the depth of the void region increase with the friction in an exponential form. The simulation results in this work help to understand the origin of the complex flow structures in moving bed particle heat exchangers.

The Development of Volcanic Ash Cloud Layers over Hours to Days Due to Atmospheric Turbulence Layering

Volcanic ash clouds often become multilayered and thin with distance from the vent. We explore one mechanism for the development of this layered structure. We review data on the characteristics of turbulence layering in the free atmosphere, as well as examples of observations of layered clouds both near-vent and distally. We then explore dispersion models that explicitly use the observed layered structure of atmospheric turbulence. The results suggest that the alternation of turbulent and quiescent atmospheric layers provides one mechanism for the development of multilayered ash clouds by modulating vertical particle motion. The largest particles, generally μ>100 μm, are little affected by turbulence. For particles in which both settling and turbulent diffusion are important to vertical motion, mostly in the range of 10–100 μμm, the greater turbulence intensity and more rapid turbulent diffusion in some layers causes these particles to spend greater time in the more turbulent layers, leading to a layering of concentration. The results may have important implications for ash cloud forecasting and aviation safety.

Tsunami-generated magnetic fields have primary and secondary arrivals like seismic waves

A seafloor geomagnetic observatory in the northwest Pacific has provided very long vector geomagnetic time-series. It was found that the time-series include significant magnetic signals generated by a few giant tsunami events including the 2011 Tohoku Tsunami. Here we report that the tsunami-generated magnetic fields consist of the weak but first arriving field, and the strong but second arriving field—similar to the P- and S-waves in seismology. The latter field is a result of coupling between horizontal particle motions of the conductive seawater and the vertical component of the background geomagnetic main field, which have been studied well so far. On the other hand, the former field stems from coupling between vertical particle motions and the horizontal component of the geomagnetic main field parallel to tsunami propagation direction. The former field has been paid less attention because horizontal particle motions are dominant in the Earth’s oceans. It, however, was shown that not only the latter but also the former field is significant especially around the magnetic equator where the vertical component of the background magnetic field vanishes. This implies that global tsunami early warning using tsunami-generated magnetic fields is possible even in the absence of the background vertical geomagnetic component.

VOF-DEM study of solid distribution characteristics in slurry Taylor flow-based multiphase microreactors

Solid particle distribution determines the reactor internal phases placement and the contact mode between catalyst particles and the liquid phase, thus plays a key role in dictating the overall performance of slurry Taylor flow-based microreactors. This study numerically investigates the distribution characteristics of particles within liquid slugs (reactors) in a vertical capillary tube, with the aim to describe the corresponding underlying mechanisms.The Volume of Fluid (VOF) method was deployed to solve the evolution of transient gas-liquid interfaces, whilst the motion of individual particles was directly tracked using the Discrete Element Method (DEM). Various fluid forces were considered based on the fully resolved Taylor flow field. Different body-fixed frames of reference were introduced to aid the analysis of the results.The particle distribution was found strongly dependent on the liquid flow field and particle physical properties, described in this study using the slurry Reynolds number (Re') and particle Stokes number (Stp), respectively. As Re' increased, the liquid flow experienced three distinctly different circulation patterns. Accordingly, three different particle distribution patterns were observed: I, particles distributed in the slug central region when Re'≤47; II, particles were trapped inside the liquid circulations for Re'∈95,190; and III, particles distributed at the edges of the liquid circulations when Re'≥379. III was the predominant particle distribution pattern in slurry Taylor flow systems. The drag force was found to be the main force governing the vertical particle motion, whilst shear lift force and horizontal drag force were the main forces driving the lateral particle motion. Generally, as Re' or Stp increased, particles tended to migrate from the core to the edge of the liquid circulations, leading to a more nonuniform particle distribution. The solid volume fraction variance (σ2) of 0.0025 could be viewed as the threshold less than which the particle distribution in the liquid slugs was considered uniform. The relatively uniform particle distribution (with σ2≤0.0025) was achievable forRe'<550 and Stp<0.1.

Parametric Resonance and Energy Transfer in Dusty Plasma

Model allowing analytical and numerical studies of a dusty plasma system is used to describe the dynamics of a monolayer of dusty particles. The mechanism of energy transfer between horizontal and vertical particle motion based on parametric resonance is described by the extended Mathieu equation. The resonance regions and growth rates of dust particles energy are obtained. The conditions for the occurrence of resonance and the initial stage of energy transfer are described more precisely based on the analysis of the obtained data. It is shown that a wide spectrum of dust particle oscillations participates in the system heating. The harmonics contributing the most to this process are determined.

Kinetics of Low Field Gradient Magnetophoresis in the Presence of Magnetically Induced Convection

Previous work (Leong et al. Soft Matter 2015, 11, 6968) has demonstrated, by using both experiments and simulations, that a magnetic field gradient can induce substantial convective currents during magnetophoresis of superparamagnetic nanoparticles in the solution. This effect substantially enhances the efficiency of low gradient magnetic separation (LGMS) processes. Throughout the LGMS process, this circulating flow plays a dominant role in homogenizing the nanoparticle solution and enhancing the vertical motion of particles. Here we perform a detailed quantitative study of the factors affecting the kinetics of LGMS in the presence of magnetically induced convection. In particular, we have found that the magnetophoretic collection rate of magnetic nanoparticles in LGMS is solely determined by the magnetic field gradient at the surface of contact of the dispersion cuvette with the magnet (denoted as the “collection plane of particles” in this work) and the area of this surface. Surprisingly, the kinetics ...

Vertical motion of particles in vibration-induced granular capillarity

When a narrow tube inserted into a static container filled with particles is subjected to vertical vibration, the particles rise in the tube, much resembling the ascending motion of a liquid column in a capillary tube. To gain insights on the particle dynamics dictating this phenomenon – which we term granular capillarity – we numerically investigate the system using the Discrete Element Method (DEM). We reproduce the dynamical process of the granular capillarity and analyze the vertical motion of the individual particles in the tube, as well as the average vertical velocities of the particles. Our simulations show that the height of the granular column fluctuates in a periodic or period-doubling manner as the tube vibrates, until a steady-state (capillary) height is reached. Moreover, our results for the average vertical velocity of the particles in the tube at different radial positions suggest that granular convection is one major factor underlying the particle-based dynamics that lead to the granular capillarity phenomenon.

Experimental study on the motions of prolate spheroidal particles under electric field

This paper presents a study on the electromechanics of prolate spheroidal conducting particles on a conducting plane. The objective of the study is to clarify the fundamental role of the non-spherical shape of particles on their behavior under electric field. We used two sizes of particles having the same major axial length but different diameter (minor axes) for the experiments. The electric field EM initiating particle motion was measured, and we found that EM was slightly higher than the theoretical field strength of the particle for rotation. The lift-off behavior of the particles at EM was different from the theoretical prediction as the particles departed from the conducting plane at significantly larger angles than the theoretical prediction. The discrepancy of the departing angle was possibly due to the predominant rotating motion of particles. With higher electric field than EM, the experimental results showed that the linear vertical motion of particles became dominant, resulting in virtually parallel lift-off of the particles. However, re-contact might occur after lift-off between the particles and the lower electrode, and increase the particle charge as a result. Charge estimation based on the lying cylindrical model is found appropriate only when a particle has a small aspect (length-to-diameter) ratio or when the field is much higher than the critical field for particle rotation.

Transverse Dynamics for Super-Rapid Acceleration in Circular High-Energy Particle Accelerators

A new particle acceleration concept had been presented to realize a short acceleration time of µs to produce high-energy muons in circular accelerators. The acceleration method is also expected to accelerate heavy-mass particles with large momentum spread: protons, deuterons, and various heavy ions. It is most important to develop a beam injection method into a main accelerator and to investigate the vertical motion of particles, especially for heavy ion acceleration. The outlines of beam injection method and beam focusing method to solve the vertical divergence problem, which causes the beam loss, are shown in this paper. In addition, a new compact magnet system, which produces magnetic field like a quadrupole field for beam focusing especially in wide aperture accelerators, is also described here.

Thickness of Saturn’s B ring as derived from seasonal temperature variations measured by Cassini CIRS

Structural and thermal properties of Saturn’s B ring and its particles are derived from orbital and seasonal temperatures variations observed by the Cassini CIRS spectrometer between 2004 and 2009 equinox. Our multiscale thermal model (Ferrari, C., Reffet, E. [2013]. Icarus 223, 28–39), which assumes negligible heat transfer by vertical motion of particles in dense rings, is adjusted to the data. Most observations were focused on the center of the B ring, at 105,000km from Saturn. A very good fit is obtained for conductive particles embedded in a moderately conductive ring medium. Assuming a bulk composition of water ice, the thermal inertia of particles is found to be Γ1=160–200J/m2/K/s1/2 and to vary with seasons as part of the heat transfer is radiative, then temperature-dependent. For the same reason, the thermal inertia of the ring, Γ0, varies with seasons, between 30 and 35J/m2/K/s1/2. It is very comparable to the thermal inertia of icy satellite surfaces. The porosity of particles p1 found to fit this thermal inertia is very high (0.93) and may emphasize an inappropriate modeling of particles by an effective porous medium. The ring filling factor is fairly high, D=0.34±0.01, but stays typical of a compact medium and compatible with the output of numerical simulations of dense ring dynamics. The thickness of the B ring at 105,000km from Saturn is estimated at HS=2.2±0.2m. The observed correlation of its optical depth with the thermal gradient between lit and unlit sides is easily reproduced by the model if the radial variations in optical depth are due to varying thickness HS(a) with constant filling factor. This thickness varies between 1 and 3m across theB2,B3 and B4 regions. It is thinner than the neighboring C ring and Cassini Division. This can be understood as a consequence of self-gravity. The ring surface mass density Σ=(1-p1)ρ0DHS(a) derived from these structural parameters is too low for a self-gravitating ring, due to the high porosity found. But its radial variations, if deduced from coupling HS(a) with known aspect-ratios H/λ of self-gravity wakes, range between 300 in the inner B ring and most certainly exceed 1000kg/m2 in the B3 ring, values compatible with a self-gravitating ring. The inferred minimum total mass of Saturn's rings is MR=1.4±0.2·1019kg, close to the mass expected for a viscous disk evolving over the age of the Solar System and compatible with current higher estimates.

Effect of vegetative canopy architecture on vertical transport of massless particles

Large-eddy simulations of approximately resolved heterogeneous vegetative canopies with repeating row structure were compared to ‘equivalent’ homogeneous simulations to explore how overall canopy density and horizontal heterogeneity influence the vertical transport of non-depositing massless fluid parcels. A Lagrangian approach was used to quantify particle dispersion. The subgrid component of particle motion was modeled with a Langevin equation that was integrated with a new semi-implicit scheme that successfully minimized rogue trajectories. With rogue trajectories controlled, the subgrid model had a negligible impact on average statistics. Analysis suggested that above the canopy top, canopy density and heterogeneity had a minor effect on mean profiles of particle concentration and vertical flux. However, increasing canopy density resulted in a linear increase in particle residence time, and increased the importance of release height on canopy escape. The average time of persistent vertical particle motions did not follow this monotonic trend. For sufficiently dense canopies, the time scale of persistent vertical motions increased with decreasing canopy density in agreement with mixing-layer scaling. As wall shear became significant, a transition was observed in which persistence decreased with decreasing canopy density. The effect of canopy heterogeneity on residence time and persistence was well correlated with the strength of dispersive fluxes. Canopy heterogeneity decreased the average time for a particle to escape the canopy, and also reduced the coherence of vertical particle motions.

A preliminary study to understand the transport process for the eggs and larvae of Japanese Pacific walleye pollock Theragra chalcogramma using particle-tracking experiments based on a high-resolution ocean model

We developed a realistic 1/50° high-resolution ocean model capable of resolving submesoscale variability, and performed particle-tracking experiments based on this ocean model to identify elements that significantly affect the transport of the eggs and larvae of the Japanese Pacific walleye pollock Theragra chalcogramma into Funka Bay. The high-resolution model reproduced representative features of the oceanographic conditions of the main spawning area and season. A comparison of particle-tracking experiments performed under the passive transport condition based on high-resolution (1/50°) and low-resolution (1/10°) ocean models showed that high-resolution modeling is essential in order to realistically simulate the transport process. In this regard, however, the vertical motion of particles cannot be explained by the passive transport condition, as it leads to unrealistically deep sinking of particles in the simulation. Turning our attention to feasible non-passive transport conditions, we then incorporated the buoyancy motion of particles and conducted additional experiments that mainly differed in the particle density adopted. We clarified that buoyancy is an important factor in the retention of particles near the sea surface, and that the ratio of the particles that remain in Funka Bay to the number of particles released is sensitive to the vertical motions/positions of the particles, implying that it is necessary to model this vertical motion more accurately by incorporating more realistic biological processes or a statistical distribution into the particle-tracking model.

Joint inversion of spatial autocorrelation curves with HVSR for site characterization in Newcastle, Australia

In order to investigate site characterization of Newcastle affected by the 1989 Newcastle Earthquake (ML = 5.6), we conducted microtremor array measurements. The spatial autocorrelation (SPAC) method was applied to estimate the S-wave velocity structure from observed microtremor data. Although the inversion of spatial autocorrelation curves is effective for estimating shallow S-wave velocity structures within the sedimentary layer, it is usually difficult to estimate the boundary between the sedimentary layer and bedrock due to a lack of amplitude of vertical components of microtremors at low frequencies. On the other hands, it is well known that horizontal to vertical particle motion spectral ratios (HVSR) have information which assists in resolving the bedrock depth and velocity. Thus, we have applied joint inversion of the spatial autocorrelation curves with HVSR to observed microtremors. Since observed HVSR curves are subject to fluctuations due to unknown Love and body wave contributions or other noise effects, there is difficulty in fitting absolute values of observed HVSR. Therefore, we evaluate observed HVSR and theoretical H/V spectra by zero-lag cross-correlation to fit the shapes of HVSR. The observed HVSR curve has accurate information for the deeper velocity structure and therefore, the estimated velocity model by joint inversion differs in velocity estimations at depth. It is concluded that the joint inversion of the spatial autocorrelation curves with HVSR is useful in practice for obtaining improved estimates of S-wave velocity models down to bedrock.

Euler–Lagrange model for scour in front of vertical breakwater

A two-dimensional Euler–Lagrange model was developed to study the scour in front of a vertical breakwater. The fluid phase was described via the Reynolds Averaged Navier–Stokes equations in conjunction with the k– ɛ turbulence closure model. The sediment phase was treated as an assembly of discrete sand grains and the scour was introduced as the motion of a granular media from the Lagrangian point of view. Motion of the sand grains was traced with a numerical code based on the so-called MBS model, in which the frequent interparticle collision described with a spring and dashpot system. Comparison between the numerical result and experimental measurement confirms that the numerical model successfully predicts the scour profile and steady streaming field. The results reveal that during the scour process sediment transport rate decrease and the scour/deposition pattern reaches to a semi-equilibrium shape. The sand grains were transported in three different modes; namely the hyper-concentrated flow, saltation and suspension mode. The concept of vertical momentum transfer is exploited to describe features of concurrently present of these different modes. It is evident that the vertical momentum transfers between upper recirculating cells of steady streaming moves the bed sediment into the upper layer; whereas the vertical motion of particles is not significantly active in the hyper-concentrated layer and the sediment grains momentum is preserved.

A three-dimensional distinct element model for bed-load transport

A three-dimensional model is developed to simulate bed-load transport using Distinct Element Method (DEM). The model describes the bed-load transport as dynamically interdependent motions of individual sediment particles under the flow action. A steady logarithmic velocity distribution over the flow depth is considered to represent fluid motion, while turbulent intensities are also included within the closure model. The present model accounts for both fluid–particle and particle–particle interactions, which are the predominant micro-mechanisms of bed-load transport under low and high tractive forces, respectively. Characteristic features of bed-load transport, previously reported by experimental observations, are numerically reproduced. The concept of vertical momentum transfer is exploited to describe features of concurrently present of saltation and sheet-flow layers. It is concluded that the vertical motion of particles is not significantly active in sheet-flow layer and the particle momentum is preserved. Consequently the interparticle collisions is the predominant mechanism of bed-load transport at high fluid tractive forces.

Effects of Multiple Modes on Rayleigh Wave Dispersion Characteristics

The effects of multiple modes on Rayleigh wave dispersion are discussed to reduce the ambiguity of uniqueness of shear wave velocity (Vs) profiles estimated by the surface wave method. Based on a review of previous studies, dispersion curves of multiple‐mode Rayleigh waves induced by harmonic vertical point loading are derived for both vertical and horizontal particle motions. Also presented is the variation with frequency of the amplitude ratio between horizontal and vertical particle motions. Numerical studies indicate that a stiff soil layer overlying a softer soil layer induces a higher mode or multiple modes, leading to an inversely dispersive characteristic. Consideration of the effects of higher modes is strongly recommended in the inverse process when the observed data show an inversely dispersive trend. The ambiguity of uniqueness of the inverted soil profiles may be reduced by using either the dispersion data of horizontal motion or the amplitude ratio of particle motions in addition to the disp...

Vapor-liquid equilibrium thermodynamics of N2 + CH4: Model and Titan applications

Calculations of the vapor-liquid equilibrium thermodynamics of the N2 + CH4 system show that the tropospheric clouds of Titan are not pure CH4, but solutions of CH4 containing substantial quantities of N2. The conditions for saturation, latent heat of condensation, and droplet composition all depend on this equilibrium. We present a thermodynamic model for vapor-liquid equilibrium in the N2 + CH4 system which, by its structure, places strong constraints on the consistency of experimental equilibrium data, and confidently embodies temperature effects by also including enthalpy (heat of mixing) data. Selected equilibrium and enthalpy data are used in a maximum likehood determination of model parameters. The model can be readily evaluated to compute the saturation criteria, composition of condensate, and latent heat in Titan's atmosphere for a given pressure-temperature (p-T) profile. For a nominal p-T profile, the partial pressure of CH4 required for formation of CH4 + N2 condensate is ∼20% lower than that required to saturate pure CH4, and ∼25% higher than that which would be computed by Raoult's law. N2 constitutes 16–30% of the cloud condensate, and higher altitude clouds are generally more N2-rich. The N2 content of condensate is ∼1/2 of that computed from Raoult's law and about 30% greater than that computed from Henry's law. Heats of condensation are ∼10% lower than for pure CH4. Above 14 km altitude, the liquid solution becomes metastable with respect to a solid solution containing less N2: freezing of liquid droplets will be accompanied by the exsolution of about 30% of the dissolved N2, probably leading to an underdense, porous texture. The refractive index, single-scattering albedo, and density of CH4 + N2 cloud droplets of the appropriate composition and phase should be used in modeling and spacecraft planning studies for Titan. Cassini investigations with sufficient altitude resolution (primarily Huygens probe experiments) can potentially detect vertical motion of particles by determining whether condensate and gas are in local thermodynamic equilibrium.

Hot-film anemometry measurement of hydroacoustic particle motion

Hydroacoustic particle motion may be detected by hot-film anemometry. Free convection causes a vertical flow that acts as a bias for vertical particle motion, resulting in a linear dependence of output voltage on the displacement. For horizontal particle motion, the output frequency is twice that of the acoustic field, and the output depends quadratically on the motion. An imposed bias flow increases the sensitivity and provides independence of the direction of gravity. The measurements are performed for water and ethylene glycol with sensors of diameters 25, 50, and 150 μm and temperature differences between sensor and medium of 15°, 30°, and 45 °C. The frequency range for horizontal motion is 20–160 Hz and for vertical motion is 20–500 Hz. The results are presented in terms of dependence of the ac Nusselt number as a function of relative displacement, Fourier number, and Rayleigh or Grashof number. At constant intensity, the output is inversely proportional to frequency to the 3/2 power for the horizontal case, and inversely proportional to the frequency for the vertical case.

Analysis of the Phase Difference Between Particle Motion Components of Sound By Teleosts

ABSTRACT The hypothesis that fish may remove 180° ambiguities concerning the sound source direction by a timing analysis between particle motion components is addressed. Analysis of the phase difference ψ (w, v) between the horizontal (v) and the vertical (w) components of the particle velocity of sound signals by teleost fish is investigated by cardiac conditioning. Standing wave sound stimuli (90 Hz) are used with ψ (w, v) = + or – 90° and equal amplitudes of v and w. The water particles move along circular trajectories for such stimuli: however, the direction of revolution is reversed in the two stimuli. These stimuli were discriminated by one whiting, one catfish and several cod, indicating that these teleosts are able to discriminate signals on a pure timing cue. If the w/v ratio is lowered, the cod can discriminate the resulting elliptical motions on the direction of revolution down to a w/v ratio of –12 dB. Moreover, down to the same w/v ratio the cod discriminates an elliptical particle motion signal from a pure translatory particle motion signal. At this level, the threshold signal-to-noise ratio for the w component is exceeded by 9 dB. Apparently phase analysis can be limited by ‘cross talk’ between horizontal and vertical particle motion detectors. The results are discussed with respect to models of directional hearing by fish.