Free-flowing Material Research Articles

Cohesional behaviours in pyroclastic material and the implications for deposit architecture

Pyroclastic density currents (PDCs) are hazardous, multiphase currents of heterogeneous volcanic material and gas. Moisture (as liquid or gas) can enter a PDC through external (e.g., interaction with bodies of water) or internal (e.g., initial eruptive activity style) processes, and the presence of moisture can be recorded within distinct deposit layers. We use analogue experiments to explore the behaviour of pyroclastic material with increasing addition of moisture from 0.00–10.00% wt. Our results show that (1) the cohesivity of pyroclastic material changes with the addition of small amounts of moisture, (2) small increases in moisture content change the material properties from a free-flowing material to a non-flowable material, (3) changes in moisture can affect the formation of gas escape structures and fluidisation profiles in pyroclastic material, (4) gas flow through a deposit can lead to a moisture profile and resulting mechanical heterogeneity within the deposit and (5) where gas escape structure growth is hindered by cohesivity driven by moisture, pressure can increase and release in an explosive fashion. This work highlights how a suite of varied gas escape morphologies can form within pyroclastic deposits resulting from moisture content heterogeneity, explaining variation in gas escape structures as well as providing a potential mechanism for secondary explosions.

Axially symmetric continuum mechanical model for the oscillon

The oscillon is a highly localized dynamical phenomenon occurring in a thin horizontal layer of granular material, which rests on a rigid plate oscillating in the vertical direction. The geometry is axially symmetric and physically resembles a splash of liquid due to a falling drop, except that it continually perpetuates itself and does not generate a spreading wave, as is the case for a liquid splash. The oscillon moves from “peak” to “crater” and “crater” to “peak” such that the time from “peak” to “peak” or “crater” to “crater” is twice the period of the oscillating plate. The physics of granular phenomena is not properly understood, and there is no continuum mechanical theory of granular materials which is widely accepted as accurately describing their behaviour. Here for a free-flowing (cohesion-less) granular material, under axially symmetric conditions, we present a partial continuum mechanical analysis assuming the Coulomb–Mohr yield function and non-dilatant double-shearing theory. We examine small perturbations superimposed upon a purely vertical vibration, and make the assumption that throughout the motion, the lower surface of the layer remains in contact with the rigid metal plate. We show how the temporal dependence, which decouples from the spatial structure, is governed by Mathieu’s equation for the physically relevant case of the rigid plate oscillating sinusoidally, and therefore stability is determined by certain key parameters. We explore a variety of possible forms for spatial dependence. The present axially symmetric analysis complements that presented by the authors for plane strain conditions, and we find, quite remarkably, that apart from constants, both flows are governed by similar fourth-order systems of ordinary differential equations. This means that for both plane strain and axially symmetry, analogous pattern forming conditions can operate.

New Procedure to Maintain Fecal Microbiota in a Dry Matrix Ready to Encapsulate.

Fecal microbiota transplantation (FMT) is one of the recommended treatments for recurrent Clostridioides difficile infection, but endoscopy and available oral formulations still have several limitations in their preparation, storage, and administration. The need for a viable oral formulation that facilitates the implementation of this highly effective therapy in different settings has led us to test the microcrystalline cellulose particles as an adsorbent of concentrated filtered fresh feces in comparison to lyophilized feces. This free-flowing material can provide protection to bacteria and results in a dried product able to maintain the viability of the microbiota for a long time. Adsorbate formulation showed a stabilizing effect in gut microbiota, maintaining bacteria viability and preserving its diversity, and is a competitive option for lyophilized capsules.

Technique for accelerated tests of samples for wear resistance

A review of the existing methods of accelerated abrasive wear tests is presented. The shortcomings of the technique implemented on an IM-01 installation of the VISKHOM design, as well as the Brinell-Howarth technique for laboratory studies, in which a powder abrasive is used are discussed, e.g., a problem of a uniform distribution of a free-flowing abrasive material over the surface of the contact zone, as well as problems of ensuring the stability of the supply of the abrasive material during the experiment. The goal of the study is to develop a methodology for comparative assessment of the wear resistance, excluding noted shortcomings. The tests were carried out on an M-1 installation using plate specimens 60 × 40 × 3 mm. The abrasive material used was a radial flap wheel 150 – 220 mm in diameter (width 30 mm, bore diameter 30 – 40 mm). The degree of wear was determined by a decrease in the mass of the sample by weighing on a balance with an accuracy of 0.1 mg before and after testing. The test results were considered as a relative wear resistance ε equal to the ratio of the wear resistance of the test specimen to the wear resistance of the reference one. The use of relative wear resistance makes it possible to increase the accuracy of the results obtained due to elimination of the influence of natural changes in external parameters that determine the intensity of wear during the test. The developed installation provides significant shortening of the accelerated comparative test (8 min) compared to 40 min on an IM-1, the structure and grain size of the working fluid, the constancy of the load in the contact zone and the speed of interaction between the sample and the tool being the same. Flap wheels of various grain sizes provide application of the device to a wide range of tasks without preliminary grinding of the samples and necessitate only their preliminary cleaning from slags and large particles after applying wear-resistant coatings.

Development of a computed tomography system capable of tracking high-velocity unbounded material through a reconstruction volume

The U.S. Army Research Laboratory (ARL) and Lawrence Livermore National Laboratory have developed a high speed computed tomography system that is capable of tracking unbounded material flux through a reconstruction volume at ballistic rates. It achieves this feat by creating three individual time-registered volume reconstructions throughout the duration of a single dynamic event. Each individual volume reconstruction is computed from five attenuation projections, which are collected using five flash X-ray sources and five digital imaging plate detectors. This work summarizes the numerous complexities in combining the 15 sources and 15 detectors into a single diagnostic, the complexities of analyzing multiple reconstruction volumes from a limited number of views, and complications associated with designing an experiment to fit within the bounding conditions of the diagnostic. It continues to demonstrate an example of how free-flowing material propagates through a reconstruction volume during a bullet/target interaction.

Теоретичне дослідження руху сипкого матеріалу в постачальному пристрої установок безперервної дії

Теоретичне дослідження руху сипкого матеріалу в постачальному пристрої установок безперервної дії

Characterization of bulk and shear properties of basmati and non-basmati rice flour.

Flours are often unstable in relation to their flow performance, which is evident when a free-flowing material ceases to flow and the processing, handling, and production parameters depend on the inherent powder characteristics and their bulk behaviour. The present study was conducted to compare the flowability of basmati and non-basmati rice flour affecting bulk handling, which could be related to its particle size, shape and surface roughness (measured by atomic force microscopy) as well as bulk and shear properties, depending upon the processing conditions. Particle size (171.1-171.9 μm) of both samples was not significantly different. However, the flowability of the non-basmati rice flour was significantly affected by its particle shape (circularity 0.487), surface roughness (124.23 nm) and compressibility (25.32%) in comparison to basmati rice flour (circularity 0.653, surface roughness 113.59 nm and compressibility 21.09%), making it more cohesive than basmati rice flour. Also, basic flow energy was significantly higher in non-basmati flour, thus requiring more energy (147.54 mJ) to flow than basmati rice flour (130.15 mJ). Overall, flowability was analysed by applying three different pressures (3, 6 and 9 kPa), among which non-basmati rice flour was found to be less flowable (flow function coefficient (FFC) 2.33 at 9 kPa) in comparison to basmati (FFC 3.35 at 9 kPa), making bulk handling difficult. This study could be useful in designing processing equipment, hoppers and silos for rice flour handling. © 2017 Society of Chemical Industry.

A comparison between powder flow property testers

In this work, three different shear testers—the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester—were compared in terms of the raw shear stress time series, yield loci points, angle of internal friction, cohesion, and unconfined yield strength. The three different powders of dolomitic lime, calcium lactate, and calcium carbonate were used for these comparisons. These three powders were characterized into different flowability classes using the Jenike classification, wherein dolomitic lime falls into the cohesive range, calcium lactate falls into the free-flowing range, and calcium carbonate falls into the very cohesive range. Results showed that the best agreement between the testers was found with moderately cohesive powders such as dolomitic lime. Furthermore, the free-flowing material tends to produce more consistent data between the three testers in terms of shear stresses and yield loci. It should be noted that the pre-shear data of free-flowing powder obtained by the Jenike shear cell must be appropriately interpreted. The largest differences between the testers are found with calcium carbonate, which is a highly compressible powder. The ways in which a high powder compressibility can differently affect the results obtained with the different testers were discussed.

The Problems of Dynamics of Wheeled Vehicles with Flow Able Building Cargo

The issues of the dynamics of the wheeled vehicles transporting free-flowing construction materials (concrete, mortar, bitumen and other construction mixes) are considered. It is proved that for the purpose of safety, the oscillations of free-flowing construction materials during the vehicle movement should be taken into account. So, in general, free-flowing construction materials are non-Newtonian fluids, i.e. their flow rheograms are non-linear. If, however, we take into account the fact that during the oscillations the deformations of non-Newtonian fluids do not occur in one plane but they do in all four coordinate planes, then the hysteresis behaviour of these rheograms is natural, which is confirmed experimentally. Then the area of ​​the hysteresis loop allows us to perform the linearization of the problem when calculating the oscillations of the dynamic system "road-vehicle-free-flowing construction materials". The oscillation analysis methods of the wheeled vehicles with free-flowing construction materials both in transversal and longitudinal planes have been developed, as well as the recommendations for increasing the stability of the wheeled vehicles against rollover and for reducing structural loads in transient motion mode of the vehicle have been given. The research allows us to consider the dynamics of the wheeled vehicles both with free flowing and solid construction materials in general. What is more, the case with a free-flowing construction material is comprehensive and the one with a solid material is specific. The developed methodology made it possible to implement a number of design solutions which improve the structural safety of the wheeled vehicles transporting free-flowing construction materials.

Reducing the Power Consumption of Ventilation Systems Through Forced Recirculation

A method of reducing dust emission and the power consumption of a ventilation system by improving the management of forced delivery of recirculated air to the charging trough is proposed. A portion of the ventilated air is fed to the charging trough, which tends to reduce the volumes of ejected air entrained by the stream of free-flowing material. The influence of the geometric parameters and the flow rate of the recirculated jet on the volume of discharged air are investigated by means of computer modeling.

The effect of operating conditions on the residence time distribution and axial dispersion coefficient of a cohesive powder in a rotary kiln

While continuous rotary calcination is a widely used thermal treatment in large-scale catalyst manufacturing, the process's heat and mass transfer mechanisms remain a challenge to characterize and to predict. Thus, the goal of this research is to improve fundamental understanding of rotary calcination to aid in the creation of a scientific methodology for process design and scale-up. For successful calcination to occur, the residence time of the particles must exceed the time required for heating and calcination at a set temperature. The optimal residence time therefore depends on both of these competing time scales, each of which is function of feed material properties, kiln geometry and kiln operating conditions. For uniform treatment of the feed, the particles must also exhibit low axial dispersion. In this work, the residence time distribution and axial dispersion coefficient for a dry cohesive fluid cracking catalyst powder were measured in a pilot plant kiln using a tracer study developed by Danckwerts. Results were successfully matched to the Taylor fit of the axial dispersion model and the Sullivan prediction for mean residence time. It was found that an increase in feed rate, kiln incline and rotary speed decreased mean residence time and overall axial dispersion. Such results have been established previously for free-flowing material like millimeter-sized extrudates, but have not been previously reported for the cohesive powders such as the one used in our work. As in free-flowing material, the axial dispersion coefficient was found to vary with kiln conditions. The values of the axial dispersion coefficients were lower for the powder than for free-flowing material, showing a dependency of axial dispersion on material properties as well as bulk flow behavior.

Heat transfer in a hybrid boiler for batch heating and radiant cooling of coke

Heat transfer within hybrid boilers for preliminary batch heating and radiant cooling of coke is considered. On the basis of experiments on an industrial prototype and model calculations, reliable values are obtained for the heat-transfer coefficients between the free-flowing material and thermal tubes. From the heat balance, the final temperature of the batch and coke is determined. In a flow-through heat exchanger, the excess heat from the coke is transmitted to water (steam) that is sent to a steam turbine for power generation. Recommendations are made regarding the heat-exchanger structure.

Improving iodine homogeneity in NIST SRM 1548a Typical Diet by cryogenic grinding

NIST SRM 1548a Typical Diet has a certified iodine mass fraction value of 0.759 mg kg−1, with a rather large expanded uncertainty (relative value 13.6 %). This might be due to the iodine inhomogeneous distribution in the pooled food material. We have proven that cryogenic grinding of NIST SRM 1548a (at the temperature of liquid nitrogen) yields a free-flowing material, with the standard deviation due to a random inhomogeneity that is lower (by a factor of 3) compared with the original material. We have also proven that no change in the certified iodine value and no contamination with other elements present (even at the sub-µg kg−1 level) occurred during the cryogenic grinding process. Thus, we have obtained a quality control material that sets up more stringent requirements on the validation and quality control procedures of the measurement of iodine mass fraction in complex food matrices.

Physical Modeling of Overall and Local Scouring of Channels Beyond Spillways of Ravine HPP

The possibility of using a finely disperse free-flowing material, the density of the substance of which is approximately that of the density of water for physical modeling of overall and local channel scouring beyond the spillway of a ravine HPP is demonstrated. The material employed for modeling of overall channel scouring should have an angle of repose in the submerged state equal to the angle in fine- and medium-grain sands.

Methods of Reducing the Power Requirements of Ventilation Systems. Part 1. Derivation of Hydrodynamic Equations of Air Ejection by a Stream of Free-Flowing Material in a Perforated Trough with Bypass Chamber

Hydrodynamic equations for the study of air recirculation in a vertical perforated tube situated in a bypass chamber as a stream of free-flowing material and ejected air travels through the chamber are obtained. The case in which recirculation of air ascending in the bypass chamber is realized both through holes in the uniform perforation of the walls of the trough as well as through the end holes at the ends of the bypass chamber is considered.

Isolation of Pharmaceutical Intermediates through Solid Supported Evaporation. Semicontinuous Operation Mode

Solid supported evaporation (SSE) is a simple, nonselective method for isolating nonvolatile compounds from a solution. The solution is put in contact with porous polymer beads onto which the compound deposits upon evaporation of the solvent. This brings some advantages over direct evaporation to dryness in terms of safety, thermal decomposition, and solid handling, as the loaded beads form a free-flowing granular material that is easily recovered. In this paper, SSE in a semicontinuous operating mode is investigated where the solution is continuously fed to (respectively sprayed over) an agitated bed of dry beads put under vacuum. It is found that under conditions where the solvent evaporation rate is high with respect to the feed rate, high bead loadings can be achieved before extensive sticking of beads and compound to the vessel walls occurs. The type of compound and solvent had little influence on the process performance, and, in cases where this was explored, the bead loading was found to be homogeneous. Based on a balance equation for the solvent fed to the system, a model is developed that results in a simple scale up criterion. The latter was successfully applied for transferring SSE from lab to the kilo lab scale.

Preparation of mixture of free-flowing materials in double-shaft paddle mixers

Results are presented for investigation of the movement of free-flowing materials in double-shaft paddle mixers. A method of reducing the mixing times of these free-flowing materials, and the design of the doubleshaft paddle mixer for this reduction, which provides for intensification of mixing due to an additional loop for particle movement are examined. Paddle mixers are widely used in various branches of industry. A number of investigations relative to mixing of freeflowing materials have been conducted in these mixers for the purpose of shortening the time required for preparation of the mixture, and improvement of its quality [1, 2]. Let us isolate two basic types of double-shaft paddle mixers: without intersection of the rotational trajectories of the paddles of the parallel shafts (Fig. 1a); and, with intersecting rotational trajectories of the paddles of the parallel shafts (Fig. 2a). It is proposed to shorten the preparation time of the mixture in the mixers with allowance for charging rules by rapid equalization of the initial components along the tiers of the effective members, intensification of convective and diffusion mixing [3, 4], and organization of large-flow discharge of the mixture without loss of its uniformity due to variation in the rotational direction of the shafts and variation of the position of the paddles on these shafts. Two methods of charging the initial components into the mixer are: uniform charging in order of decreasing sizes (the concentration of initial components in each tier of effective members is essentially the same); and, simultaneous charging via different devices (positioning of the initial components is strictly isolated with respect to the tiers of effective members) [4]. Let us examine a mixer (see Fig. 1a) in the housing of which paddles 2 are located on shafts 1 such that the material is mixed from one terminal section of the mixer in one direction, and to the other terminal section in the other direction, while at the end, one or two pairs of paddles are mounted at the opposite angle for agitation of the mixture in the opposite direction. The rotational trajectory of paddles 2 on shafts 1 do not intersect. The interaxial distance between the shafts a 1 > 2R (R is the radius of the rotational trajectory of the paddles). For the method of simultaneous loading of the initial components, a largeflow counter-movement of particles 3 is formed from one terminal section to the other in the initial stage to equalize their concentration along the shafts in each tier of effective members, and intensify convective mixing (see Fig. 1b). Shafts 1 rotate in opposite directions, displacing the free-flowing material from the center of the mixer toward the lateral walls of the housing. Formation of zones of material slip (A) is possible near the terminal walls of the housing in the mixer, resulting in a nonuniform load over the length of the shaft, and slowing of the process of uniform movement of the material. Movement of material is insignificant between the effective zones of the shafts; this renders equalization of the concentration of initial components difficult within the entire reaction space (see Fig. 1b). Charging requires organization within the central zone along the mixer. The charging consumes from 0.1 to 0.3 of the total time required for mixing. To intensify diffusion mixing, the direction of rotation of the shafts is reversed, mixing the material from the lateral walls of the housing toward the center of the mixer. Active exchange of particles occurs between the opposing flows in the central portion of the mixer (see Fig. 1c).

Subcuticular Urate Accumulation in an American Lobster (Homarus americanus)

An unusually "lumpy" lobster, Homarus americanus, was presented to the Atlantic Veterinary College Lobster Science Centre for evaluation. The lobster was weak with numerous pale, raised, and flat areas (diameter, 3-15 mm) on the exoskeleton, some of which were ulcerated. On postmortem examination, the pale areas corresponded to accumulations of viscous to free-flowing white material, which was found in only the subcuticular connective tissues. No internal organs were affected. Direct light examination of nonstained impression smears of the material showed abundant crystals resembling uric acid, amorphous urates, and sodium urate, which were readily soluble in 1 M potassium hydroxide. Wright-Giemsa stained imprints showed numerous fine, rounded, nonstaining granules free in the background and within individual round cells. Fourier-transformed infrared spectroscopy confirmed the presence of urates or mixed urate salts. Hemolymph plasma urea (1.7 mmol/liter) and uric acid (287 μmol/liter) concentrations were slightly higher than those seen with 36-hour emersion. Histologic sections showed aggregates of vacuolated mononuclear cells in the loose subcuticular connective tissue occasionally infiltrating between underlying muscle fibers. Grossly visible urate deposits are occasionally documented in land crabs and rarely reported in the blue crab; none, however, are associated with deformation of the cuticle. Possible etiologies include increased uric acid intake or production or decreased excretion. Anecdotal reports of similarly affected lobsters have been received but are intermittent and undocumented.

Fractal theory of dome formation

This study presents a theoretical model of dome formation during nonsteady flow of polydisperse cohesive free-flowing materials using fractal structures simulating deterministic relationships. A procedure is proposed for analysis of dome shapes based on fractal theory of nonsteady flow. Experimental data on determination of dome shape for a model free-flowing material, which have demonstrated higher accuracy of the proposed method as compared with existing ones, are cited.

Molding of powder materials with a laminar internal structure

A scheme for layer-by-layer molding of composition materials using a pressing tool is examined for the production of cylindrical articles (pressings). A characteristic compression curve of a free-flowing material is presented. The variation in the dilatational strain of the powder due to the molding pressure is analyzed. The problem involving determination of the stress distribution and densities of free-flowing materials on the basis of the volume of a pressing consisting of n layers is solved analytically. Computational diagrams of the molding and equations for determination of the height of the pressing are given.