Flow Behavior Of Mixtures Research Articles

Flow Behavior of Complex-Shaped Particle Mixtures in Rotary Drums: A DEM Study

Metal matrix composites hold great potential as functional materials for energy conservation applications. These composites are manufactured using powder metallurgy, which involves the incorporation of fine particles with diverse shapes. Understanding the flowability of particle mixtures with varying shapes is crucial for optimizing industrial processes. This study focuses on analyzing the flowability and flow behavior of mixtures composed of alumina and aluminum alloy particles using the discrete element method. The particle shapes are modeled to closely resemble actual particles, and their flow behavior in a rotating drum is simulated. The upper and lower dynamic angles of repose, outlines of particle bed surface, particle displacements, and particle velocity distributions were analyzed to understand the flow characteristics of complex-shaped particles. The results reveal the influence of particle shape on the flow behavior of powder mixtures, providing valuable insights for process optimization and design.

Shape-dependent calculation of specific surface area of aggregates versus X-ray microtomography

The specific surface area (SSA) of constituents in a concrete mixture has a significant effect on its workability in fresh state. Excess layer theories relate the SSA to the flow behaviour of mixtures and can be used as part of an approach to mix design. However, measurement of SSA is complex and includes several issues, and thus is commonly replaced by mathematical estimation of the parameter. The mathematical approximation of surface area is based on the assumption of a spherical shape for the particles, which leads to failure of taking into account the effect of shape and the square–cube law. The article explores the possibility of replacing the assumption of a spherical shape with that of Platonic solids as the representative shape to account for the angularity of aggregates. The calculation was conducted based on information on the particle size distribution (PSD) obtained from dry sieving method. A calculated surface area on the assumption of a dodecahedron shape for natural aggregates and a cubical shape for crushed aggregates showed good agreement with SSA measurements conducted by X-ray microtomography. Furthermore, the effect of changes in PSD on the accuracy of the approach was also studied. It was found that the estimated value of SSA was improved in comparison with the traditional way of calculation on the assumption of a spherical shape.

Rheology of cubic particles in a concentrated colloidal dispersion suspending medium

The flow behavior of mixtures of micron‐sized cubic particles suspended in a concentrated colloidal dispersion is investigated across a broad range of cubic particle concentrations. In the semi‐dilute regime, the qualitative shape of the dynamic moduli and flow curves reflect those of the underlying colloidal dispersion medium. These curves are superimposed with the underlying colloidal dispersion using shift factors that are found to be larger than those obtained in a recent study of suspensions of non‐colloidal spherical particles in the same colloidal dispersion medium. At higher concentrations of cubic particles, deviations from this shifting procedure are apparent. Scaling calculations suggest depletion interactions are responsible for the increase in the low shear viscosity and confinement of the underlying colloidal dispersion can be expected to enhance the shear thickening behavior at high shear stresses. The results of this study provide guidance for formulating suspensions through control of particle shape and mixture concentration. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1091–1101, 2017

Relationship between the cohesion of guest particles on the flow behaviour of interactive mixtures

In this study, we aimed to investigate the effects cohesion of small surface-engineered guest binder particles on the flow behaviour of interactive mixtures. Polyvinylpyrrolidone (PVP) – a model pharmaceutical binder – was spray-dried with varying l-leucine feed concentrations to create small surface-engineered binder particles with varying cohesion. These spray-dried formulations were characterised by their particle size distribution, morphology and cohesion. Interactive mixtures were produced by blending these spray-dried formulations with paracetamol. The resultant blends were visualised under scanning electron microscope to confirm formation of interactive mixtures. Surface coverage of paracetamol by guest particles as well as the flow behaviour of these mixtures were examined. The flow performance of interactive mixtures was evaluated using measurements of conditioned bulk density, basic flowability energy, aeration energy and compressibility. With higher feed l-leucine concentrations, the surface roughness of small binder particles increased, while their cohesion decreased. Visual inspection of the SEM images of the blends indicated that the guest particles adhered to the surface of paracetamol resulting in effective formation of interactive mixtures. These images also showed that the low-cohesion guest particles were better de-agglomerated that consequently formed a more homogeneous interactive mixture with paracetamol compared with high-cohesion formulations. The flow performance of interactive mixtures changed as a function of the cohesion of the guest particles. Interactive mixtures with low-cohesion guest binder particles showed notably improved bulk flow performance compared with those containing high-cohesion guest binder particles. Thus, our study suggests that the cohesion of guest particles dictates the flow performance of interactive mixtures.

Coarse particle support in turbulent flow of visco-plastic carrier

The paper deals with a flow behaviour of mixture composed of coarse glass-bead particles and non-Newtonian carrying liquid of Herschel-Bulkley type in a pressurized pipe. Essentially, there are two mechanisms governing support of particles in the flowing carrier: mutual inter-particle collisions and interaction of particles with carrier turbulent eddies. The turbulent support is quantified by a turbulent-diffusion model, which predicts a distribution of concentration of particles in the flow. In the model, the particle turbulent diffusivity is an important parameter dependent on a number of flow quantities, e.g. the carrier rheological parameters. In case of Newtonian carrier, the viscosity is the only rheological parameter and it is constant throughout the flow. In the non-Newtonian carrier, however, local values of the viscosity vary with the shear strain and so affect the particle diffusivity. The paper discusses experimental and analytical results for non-Newtonian mixture flows of measured rheological parameters and flow characteristics. Based on measured concentration profiles, a suitable method is used to determine the local particle diffusivity experimentally.

Analysis of extrusion of some wet powder masses used in extrusion/spheronisation

The extrusion flow behaviour of mixtures of lactose, microcrystalline cellulose (MCC) and water in the ratio 5:5:6 by weight has been analysed from data previously obtained by a ram extruder for powder and colloidal grades of MCC. The analysis followed a recent approach of examining the viscous and elastic behaviour of polymers. Results suggest that at low flow rates, mixtures containing colloidal grades of MCC have significantly higher shear viscosities than powder grades. The present analysis also shows that shear thickening of some mixtures occurs. Elongational flow was also examined together with entry flow to the die. The results of the analysis indicate that: (a) particle size of the MCC is not important, (b) the greatest extrudate distortions occur for systems having relatively low shear viscosities at low flow rates. There appears to be an optimal elasticity for the formation of satisfactory spheres in the spheronisation stage, i.e. they must neither be too elastic nor have low elasticity.

Extrusion Stresses, Die Swell, and Viscous Heating Effects in Double‐Base Propellants

A capillary extrusion rheometer was used to evaluate the flow behavior of mixtures of nitrocellulose (12.2% nitrogen) and nitroglycerine when processed using solvent blends of different strengths. The aim of the work was to quantify the effects on flow behavior of “gelatinization,” that is, the degree of breakdown of the fibrous structure of the nitrocellulose. The flow behavior was measured over a range of extrusion temperatures. The results indicate that the materials behave as Herschel‐Bulkley fluids, that the shear stress decreases as gelatinization increases, and that viscous heating is more apparent in poorly gelatinized doughs. Surface temperatures of the extrudate determined experimentally are compared with computer‐modelled values. Die swell measurements decreased with decreasing degree of gelatinization and with increasing extrusion temperature.

Void Fraction and Flow Pattrn during Two-Phase Flow of Pseudoplastic Fluids

Void fraction and flow pattern studies have been carried in order to clarify the role of turbulence promotors and the effect of pipe diameter on the flow behaviour of mixtures of power-law fluids and air in circular pipes. Void fraction data are analysed using the information available for Newtonian fluids. It is interesting to note that turbulence promoters do not affect the void fraction. Marked discrepancies in the void fraction data can be explained in terms of the different flow patterns present. High speed photographic techniques were used to analyse the behaviour of the flow in 21.7 mm diameter pipes. Visual studies of the flow patterns are described for pipes of 36.5 mm diameter.

Rheological behaviour of mixtures of rubber and crumb from scrap pneumatic tyres

In continuation of earlier studies the flow behaviour of mixtures of rubber (SBR, EPDM) and crumb from scrap tyre treads was estimated at 120°C with the aid of a high-pressure capillary rheometer. The influence of the capillary dimension on the flow curves was studied. With narrow and short capillaries the flow behaviour proved to be independent of the filler concentration. At low shear rates a discrimination of the flow characteristics according to the filler loading was observed only with capillaries above a certain width and length. At high shear rates with such a capillary an inversion of the rating of the flow curves was found.