The penetration behaviour of impacting particles into glycerol solutions has been studied. A high-speed video technique has been used to observe the particle motion during penetration and to measure the transient displacement of the particle. The experimental range is 10 less than or equal to Re-0 less than or equal to 61 000, 410 less than or equal to Fr-0 less than or equal to 70 000 and 0.287 less than or equal to rho' less than or equal to 0.953, where Re-0, Fr-0 and rho' are the particle Reynolds number (nu(0)d(p) rho/mu), the particle Froude number (nu(0)(2)/d(p)g) and the solid to liquid density ratio (rho(p)/rho) respectively. Comparing a solution of an equation of motion for a particle penetrating a liquid interface with the corresponding experimental results revealed that the standard drag coefficients are inappropriate to represent particle impacts owing to the dynamic nature of the flow, This effect was more pronounced with increasing rho', The critical condition for particle penetration is Re-0 approximate to 250.

The aluminium flyash metal matrix composite (flyash MMC) of A380 alloy was produced by a low cost full liquid route. The tensile strength and hardness properties of up to 20% (vol.) flyash particles (microspheres) in flyash MMC were measured. The volume fraction and the distribution of flyash microspheres in the flyash MMC were determined by an image processing technique. The results show that both the tensile strength and the hardness of the flyash MMC decrease with increasing microsphere volume fraction in the flyash MMC which is likely due to the presence of porosity and debonding. The microstructure of the fracture surface of the tensile test specimens suggests that debonding between the microspheres and aluminium matrix is the main reason for this lowering of the mechanical properties. However, strength to weight ratio of the flyash MMC is similar or marginally better than the pure alloy. The measured density of the flyash MMC was found to be 15% to 20% lower than the matrix alloy.

A fundamental aspect of submerged powder injection into melts which is not well understood is the extent to which the particles separate from the carrier gas upon injection, particularly under high solids loading conditions. In this study, the injection of nonwettable powders was investigated using a cold-model system at solids loadings from 1 to 25. Polyethylene powder was injected through a top-submerged lance into a cylindrical water bath under bubbling conditions. Air was used as the carrier gas. The apparatus was designed so that the particles remaining with the gas phase could be collected separately from those which escaped from the bubbles. The gas velocity (5.15 to 10.3 m/s), surface tension (0.03 to 0.072 N/m), lance diameter (4.7 to 7.4 mm), and particle size (< 500 μm) were independently varied. The separation of the powder from the primary gas bubbles was found to increase with increasing solids loading when the gas velocity, surface tension, and lance diameter were held constant. At constant solids loading, the separation increased with increasing gas velocity, increased with increasing lance diameter, and decreased with increasing surface tension. The separation was found to be independent of the particle size of the powder in the range of solids loadings tested. A theoretical relationship between the penetration efficiency and the particle jet Weber number successfully correlated with the experimental data.

Alloys of nickel and zinc are used for the hot dip galvanizing of reactive steels containing around 0.1 pct Si. The production of these alloys is hindered by the low solubility of nickel in molten zinc at normal zinc alloying temperatures (450 °C to 550 °C). The kinetics of the dissolution of nickel in molten zinc were investigated in the temperature range 450 °C to 550 °C to show that the dissolution rate is controlled by mass transfer in the liquid boundary layer. The experiments involved dipping nickel plates into a crucible of zinc, which could be rotated to provide controlled convection around the stationary nickel plates. The dissolution rate of nickel plates immersed vertically in a static zinc melt was measured to determine the diffusion coefficient of nickel in zinc as a function of temperature and the activation energy of diffusion. A mathematical model was formulated to predict the dissolution time of nickel particles suspended in molten zinc. The dissolution times observed during plant-scale alloying tests to produce 0.15 wt pct Ni alloys using powder injection to introduce the nickel into the zinc melt agreed with the predictions of the mathematical model. The plant tests demonstrated that alloying times of less than 10 minutes can be achieved at normal alloying temperatures if the nickel is added as a powder.

Many slag treatment processes use injection of solid reductants into slag baths to recover metal values. In the present laboratory study, the effect of selected injection parameters such as lance diameter, gas flowrate, coal particle size and slag bath temperature have been investigated, and the behaviour of different types of reductant in slag fuming has also been considered. Coal laden gas discharge through a lance into a slag bath has been monitored by a pressure transducer. The pressure traces have revealed that the slag bath viscosity changes as fuming progresses. High momentum coal injection, a thin wall lance, intense bath agitation and increasing temperature all improve the fuming rates. Natural gas was found to be a better reductant than coal and brown coal char.

Factors affecting bubble overlap (interaction) in multipoint (multituyere/lance) gas-injection systems such as the Pierce-Smith converter and the zinc-fuming furnace have been investigated in laboratory room-temperature modeling experiments and at the industrial scale. Pressure changes have been recorded simultaneously from adjacent tuyeres both in the laboratory and in plant trials. It has been found that the factors which influence bubble overlap include the tuyere separation to tuyere diameter ratio, gas injection velocity, gas and liquid properties, and position and orientation of the tuyeres.

Submerged injection is a unit operation in which solids are injected through a lance (pipe) or a tuyere using a conveying gas into a metallurgical bath for refining and smelting of metals. A critical aspect of solids injection is the behaviour of gas and particles in the injector prior to their entry into the melt. The influence that gas velocity, particle density, particle size, lance length, and solids loading has on the exit velocity of the solids at the lance tip were investigated. The exit solids velocities were measured using an infra-red velocity probe. Comparison of these results with a mathematical model developed from a force balance on an accelerating single particle showed that the model predicted the exit solids velocity reasonably accurately (+ 2.5%) for conditions of low solids loadings. The ratio Us /Ug at the lance tip is not constant as reported by previous workers, but determined by the particle density, particle size and the injector length.

The injection of nonwettable powders into melts in the bubbling regime was studied experimentally using a cold-model system. Polyethylene powder was injected into a cylindrical vessel containing water, through a vertical top-submerged lance, with insoluble (air) and soluble (ammonia) carrier gases. The concentration of particles in the liquid and the penetration length of the particle-liquid jet into the bath were measured, as the carrier gas composition, the gas and solids flow rates, and the particle size were varied. It was found that the concentration of particles retained in the liquid was up: to 1.0 times higher, and the penetration length of the jet was up to three times higher when the soluble carrier gas was used instead of the insoluble carrier gas. For both carrier gases, the dispersed particle concentration increased with increasing gas flow rate and increasing particle size, whereas the penetration length of the jet increased with increasing gas and solids flow rates.

Smelting and refining operations commonly employ submerged gas injection with and without solid powder reactants to obtain efficient gas/liquid and liquid/solid contacting. However, a number of ferrous and nonferrous operations continue to be troubled by such problems as tuyere blockage, low refractory life, variable gas efficiency and uncontrolled and inefficient solid injection leading to environmental problems. In this paper recent development work involving physical and mathematical modelling and plant trials on the process engineering aspects of some conventional and new processes are presented. Modifications to plant practice to overcome current problems are discussed.

The throughput of casting plants in the metallurgical industry is limited by the slow rate of dissolution of some high melting point alloying agents in alloying ladles or holding furnaces prior to casting. In this paper, a mathematical model of the dissolution of high melting point additives is presented, and a convenient graphical method for estimating the dissolution time is described. An operating region diagram for alloying is developed from which optimum conditions for a specified system can be selected.

A novel experimental technique which can physically model the powder injection process to determine the recoveries of injected powders has been described here. At low solids loading powder recovery depends on particle loading, velocity, density and size. However, at high loadings a strong dependence of recovery on these variables was not observed.

The behavior of gas discharging into melts at high velocities but still in the bubbling regime has been investigated in a laboratory modeling study for constant flow conditions. Air or helium was injected through a vertical tuyere into water, zinc-chloride, and aqueous glycerol solutions. High speed cinematography and pressure measurements in the tuyere have been carried out simultaneously. Pressure fluctuations at the injection point were monitored and correlated to the mode of bubble formation. The effects of high gas flow rates and high liquid viscosities have been examined in particular. Flow rates were employed up to 10-3 m3/s and viscosity to 0.5 Ns/m2. In order to attain a high gas momentum, the tuyere diameter was only 3 x 10-3 m. The experimental conditions and modeling liquids were chosen with special reference to the established practice of submerged gas injection to treat nonferrous slags. Such slags can be highly viscous. Bubble volume is smaller than that calculated from existing models such as those given by Davidson and Schüler10,11 due to the effect of gas momentum elongating the bubbles. On the other hand, viscosity tends to retard the bubble rise velocity, thus increasing volumes. To take elongation into account, a mathematical model is presented that assumes a prolate ellipsoidal shape of the bubbles. The unsteady potential flow equations for the liquid are solved for this case. Viscous effects are taken into account by noting that flow deviates from irrotational motion only in a thin boundary layer along the surface of the bubble. Thus, drag on the bubble can be obtained by calculating the viscous energy dissipation for potential flow past an ellipse. The time-dependent inertia coefficient for the ellipsoid is found by equating the vertical pressure increase inside and outside the bubble. This pressure change in the bubble is obtained by assuming that gas enters as a homogeneous jet and then calculating the stagnation pressure at the apex of the bubble.