S. Joseph Antony

Modeling of agglomerate behavior under shear deformation: effect of velocity field of a high shear mixer granulator on the structure of agglomerates

Abstract -High shear mixer granulators are typically found in pharmaceutical and detergent industries, and are capable of reducing processing time and producing agglomerates with high strength and density. Generally, several granulation scaling-up stages are involved before reaching the production level. This is conducted to exert better understanding, control and optimization at the smaller scales before proceeding to the larger scales in terms of geometric, kinematic and/or dynamic similarities. During granulation scaling-up stages, the mechanics of particle interactions and the prevailing level of compressive stresses and strains within the granulator are affected by the variation in hydrodynamics of the granulator as a result of different scales. This in turn affects the final structure of the agglomerates. In this paper we analyze the effect of velocity field of two different scales of high shear mixer granulator (1 and 5 l) on the structure of the evolved agglomerates. The study is based on computer simulation using the discrete element method (DEM). A single agglomerate is generated using DEM computer code and is placed in a bed of primary particles. A velocity field is then superimposed on the surrounding particles. This velocity field corresponds to that obtained experimentally from a separate study using Positron Emission Particle Tracking analysis on 1- and 5-l granulators which were scaled up based on the condition of constant shear stress. The results show that when the velocity profile of the 1-l granulator is used the agglomerate becomes more elongated and it has a smaller packing fraction. Therefore the agglomerate would be weaker.

Imaging shear stress distribution and evaluating the stress concentration factor of the human eye.

Healthy eyes are vital for a better quality of human life. Historically, for man-made materials, scientists and engineers use stress concentration factors to characterise the effects of structural non-homogeneities on their mechanical strength. However, such information is scarce for the human eye. Here we present the shear stress distribution profiles of a healthy human cornea surface in vivo using photo-stress analysis tomography, which is a non-intrusive and non-X-ray based method. The corneal birefringent retardation measured here is comparable to that of previous studies. Using this, we derive eye stress concentration factors and the directional alignment of major principal stress on the surface of the cornea. Similar to thermometers being used for monitoring the general health in humans, this report provides a foundation to characterise the shear stress carrying capacity of the cornea, and a potential bench mark for validating theoretical modelling of stresses in the human eye in future.

Photonics and fracture toughness of heterogeneous composite materials

Fracture toughness measures the resistance of a material to fracture. This fundamental property is used in diverse engineering designs including mechanical, civil, materials, electronics and chemical engineering applications. In spite of the advancements made in the past 40 years, the evaluation of this remains challenging for extremely heterogeneous materials such as composite concretes. By taking advantage of the optical properties of a thin birefringent coating on the surface of opaque, notched composite concrete beams, here we sense the evolution of the maximum shear stress distribution on the beams under loading. The location of the maximum deviator stress is tracked ahead of the crack tip on the experimental concrete samples under the ultimate load, and hence the effective crack length is characterised. Using this, the fracture toughness of a number of heterogeneous composite beams is evaluated and the results compare favourably well with other conventional methods using combined experimental and numerical/analytical approaches. Finally a new model, correlating the optically measured shear stress concentration factor and flexural strength with the fracture toughness of concretes is proposed. The current photonics-based study could be vital in evaluating the fracture toughness of even opaque and complex heterogeneous materials more effectively in future.

Visualising Shear Stress Distribution inside Flow Geometries Containing Pharmaceutical Powder Excipients Using Photo Stress Analysis Tomography and DEM Simulations

For the first time, photo stress analysis tomography (PSAT) is applied to probe the distribution of maximum shear stress and direction of major principal stress field within ‘powder’ assemblies inside hopper geometries, and further supported by discrete element model (DEM) simulations. The results show that for decrease in hopper angle, the direction of major principle stress aligns with the direction of gravity which could promote flow rate under dynamic conditions. Conversely, the propensity of developing relatively more non-homogeneous distribution of shear resistance zones inside powder assemblies increases with the hopper angle, which could subsequently decrease their macroscopic flow rate.

Strength and Durability of Composite Concretes with Municipal Wastes

The influence of different types of polyethylene (PE) substitutions as partial aggregate replacement of micro-steel fiber reinforced self-consolidating concrete (SCC) incorporating incinerator fly ash was investigated. The study focuses on the workability and hardened properties including mechanical, permeability properties, sulfate resistance and microstructure. Regardless of the polyethylene type, PE substitutions slightly decreased the compressive and flexural strength of SSC initially, however, the difference was compensated at later ages. SEM analysis of the interfacial transition zone showed that there was chemical interaction between PE and the matrix. Although PE substitutions increased the permeable porosity and sorptivity, it significantly improved the sulfate resistance of SCC. The influence of PE shape and size on workability and strength was found to be more important than its type. When considering the disposal of PE wastes and saving embodied energy, consuming recycled PE as partial aggregate replacement was more advantageous over virgin PE aggregate replaced concrete.

Flow behaviour of grains through the dosing station of spacecraft under low gravity environments

AbstractFor the design of the grain-processing stations of spacecrafts, such as EXOMARS 2020, reliable estimates are required on the internal and bulk flow characteristics of granular media under l...

Molecular Dynamics Study of Anatase TiO2 Nanoparticles in Water and Vacuum Environments

Nanoparticles are nanometer sized metallic oxides which possess enhanced properties that are desirable to a wide range of industries. In this study, we investigate structural and surface properties of anatase TiO2 nanoparticles in vacuum and water environments using molecular dynamics simulations. The particle sizes ranged from 2 to 6 nm and simulations were performed at 300 K. Surface energy of the particles in vacuum was seen to be higher than that of the particles in water by about 100% for the smaller particles (i.e. 2 and 3nm) and about 60% for the larger particles (i.e. 4 to 6 nm). Surface energy of the particles in both environments, is seen to increase to a maximum (optimum value) as the particle size increases after which no further significant increase is observed. In vacuum, studies carried out at temperatures ranging from 300–2500 K showed a high dependence of surface energy on temperature. The estimated surface tension of water is seen to agree quite well with that of experiments.Copyright