Experimental Simulation of Particulate dispersion in Sand-Water Slurry System in Mechanically Agitated Metallurgical Vessel

Simulation by dispersion of sand particles in water in an impeller stirred vessel has been carried out with a view to establish parameters for effective dispersion of dispersoids in Mg- Metal Matrix Composites by liquid metallurgy route. The effect of z-distance (height of the impeller from the base of the vessel) and rotational speed on the degree of dispersion has been studied and the results are reported in this paper

Physical modelling of particle distribution for stir cast metal matrix composite using sand-water and sand - aqueous CaCl2 slurry system

Suspension characteristics of particle is a very important aspect in many industrial processes such as waste water treatment, composite making by stir cast technique, mineral and chemical engineering processes. In some cases, homogeneous mixing is desirable, in other cases,either floatation or sedimentationis desimble. Although apparently the phenomenon seems to be very simple, but tailoring the particle movement as desired is not easy.The complexityarises becausethe particlesuspension chamcteristics depends upon a number of factors viz. particle shape, size and size distribution, specific gravity, its concentmtion; nature of liquid i.e. its specific gravity, viscosity and surface tension; vessel and stirrer geometry and also the design and process variables. Moreover various forces such as gravity, buoyancy, centrifugal, viscous drag and frictional forces due to collision of particles jointly act on a particle under dynamic rotating motion of the fluid. There is a tendency of hindered settling of particles when its amount is relatively higher than a critical value. In the present study, sand-water slurry system was taken and stirred by a propeller type of stirrer in a cylindrical shaped perspex vessel of diameter 0.1Omx 0.15m height, the average particle size being 200 microns of mostly sub-angular to rounded shape. Some studies were also done using a bigger vessel of diameter 0.20 m x 0.30 mheight with sand-water and sand-aqueous CaCI2(density 1330 KglmJ)systems. Various factors such as particle size and distribution, its amount, speed of rotation and power input to stirrer, its location in the vessel, direction of rotation of stirrer were varied and their influences on air-entrainment, piping, layering (single phase zones of particles), sedimentation and overall particle distributionwere investigated which is a difterent approach in comparison with the earlier investigations. The distribution was assessed qualitatively (visually and photogmphically through perspex)and quantitatively by measuring the concentration and sieve analysis of the samples drawn from different locations along the height of the slurry column. Finally a suspension model in terms of particle size distributio~ was made under various conditions studied. The degree of uniformity of particle distribution is found to be strongly dependent upon stirrer speed as well as the distance between the vessel bottom and the stirrer base. Particle distribution was found to be better in sand-aqueous CaCI2 slurry thanin sand-water system. This suspension model can be extended to metallic system considering non-dimensional pammeters such as Reynolds Number, Archemides Number, Lyaschenko Number, Froude Number. Up-scaling is also possible using various similitude criteria

Effect of some design parameters on the suspension characteristics of a mechanically agitated sand–water slurry system

Suspension characteristics of a slurry system depends, to a large extent, upon the design parameters apart from the process parameters. Lack of data for application in the metallic system prompted the authors to study this transparent modeling using a sand–water slurry system stirred in a cylindrical vessel of 10 cm diameter×20 cm height. In this study, the effect of some important design parameters such as the type of stirrer, angle and shape of blades, direction of rotation of stirrer, number of stages of impeller, baffle condition and the process parameters, namely, power input, rev./min and location of stirrer, etc., were investigated and optimised. This study is expected to help in understanding the suspension characteristics of the solid liquid slurry system used in metallurgical processes such as composite making by the liquid metallurgy technique

A simple technique for measurement of apparent viscosity of slurries: sand-water system

Measurement of apparent viscosity for rheological fluids is extremely important for a variety of industrial processes such as transportation of slurries in mineral processing, petrochemical and chemical processing, rheocasting of metal matrix composite, etc. In the present work, a sand-water slurry system of varying sand concentration was taken up as a model rheological fluid. The apparent viscosity was measured under dynamic flow conditions and varying shear strain rate using a simple technique of impeller viscometry. From the measurement of impeller speed, impeller and vessel configuration and power input data, a correlation was developed for the apparent viscosity of the non-Newtonian sand-water slurry system employing Reynolds number and power number. The values of apparent viscosity obtained from the above correlation compared reasonably well with the experimental observations by the same authors and also the literature data for a similar slurry system. The technique reported in this paper can be effectively used to measure apparent viscosities of slurries which do not exhibit any flocculating, coagulating or degenerating behaviour under shear within the laminar and transition regime of fluid flow. (C) 2002 Elsevier Science Ltd. All rights reserved