Preparation of o/w emulsions stabilized by solid particles and their characterization by oscillatory rheology

The purpose of this investigation was to examine the preparation and characterisation of hexane-in-water emulsions stabilised by clay particles. These emulsions, called Pickering emulsions, are characterised by the adsorption of solid particles at the oil/water (o/w) interface. The development of an elastic film at the o/w interface following the adsorption of colloidal particles helps to promote emulsion stability. Three different solid materials were used: silica sand, kaolin, and bentonite. Particles were added to the liquid mixtures in the range of 0.5–10 g dm−3. Emulsions were prepared using o/w ratios of 0.1, 0.2, 0.3, and 0.4. The effect of sodium chloride, on the stability of the prepared emulsions, was assessed in the range of 0–0.5 mol dm−3. In addition the use of a cationic surfactant hexadecyl-trimethylammonium bromide (CTAB) as an aid to improving emulsion stability was assessed in the concentration range of 0–0.05% (w/v). Characterisation of emulsion stability was realised through measurements of rheological properties including non-Newtonian viscosity, the elastic modulus, G', the loss modulus, G", and complex modulus, G*. The stability of the emulsions was evaluated immediately after preparation and 4 weeks later. Using the stability criteria, that for highly stable emulsions: G' > G" and both G' and G" are independent of frequency (varpi) it was concluded that highly stable emulsions could be prepared using a bentonite concentration of 2% (or more); an o/w ratio greater than 0.2; a CTAB concentration of 0.01%; and a salt concentration of 0.05 M or less—though salt was required.

Computational modelling of bubbles, droplets and particles in metals reduction and refining

The CFD modelling of metals reduction processes particularly always seems to involve the interaction of liquid metals, a gas (often air) top space, liquid droplets in the top space and injection of both solid particles and gaseous bubbles into the bath. These phases all interact and exhange mass, momentum and energy. Often it is the extent to which these multi-phase phemomena can be effectively captured within the CFD model which determines whether or not a tool of genuine use to the target industry sector can constructed. In this paper we discuss these issues in the context of two problems - one involving the injection of sparging gases into a steel continuous caster and the other based on the development of a novel process for aluminium electrolysis.

Computational modelling of bubbles, droplets and particles in metals reduction and refining

A multi-phase framework is typically required for the CFD modelling of metals reduction processes. Such processes typically involve the interaction of liquid metals, a gas (often air) top space, liquid droplets in the top space and injection of both solid particles and gaseous bubbles into the bath. The exchange of mass, momentum and energy between the phases is fundamental to these processes. Multi-phase algorithms are complex and can be unreliable in terms of either or both convergence behaviour or in the extent to which the physics is captured. In this contribution, we discuss these multi-phase flow issues and describe an example of each of the main “single phase” approaches to modelling this class of problems (i.e., Eulerian–Lagrangian and Eulerian–Eulerian). Their utility is illustrated in the context of two problems – one involving the injection of sparging gases into a steel continuous slab caster and the other based on the development of a novel process for aluminium electrolysis. In the steel caster, the coupling of the Lagrangian tracking of the gas phase with the continuum enables the simulation of the transient motion of the metal–flux interface. The model of the electrolysis process employs a novel method for the calculation of slip velocities of oxygen bubbles, resulting from the dissolution of alumina, which allows the efficiency of the process to be predicted.

Characterising noise signals in 2-phase solid gas flows

Pneumatic conveying of powder and granular material involve the mixed flow of solid particles in air. Characterisation of solid/gas flow regimes is important for the design, operation and control of plants involving such two-phase processes. This paper describes preliminary studies directed at identifying flow regimes in solid/gas flows by analysis of the process `noise' signals from a flow transmitter which has a relatively wide frequency response.

Electrostatic modelling and measurement of airborne particles concentration

Granular air-borne particles generally carry very small amounts of electric charge as a consequence of charging by the triboelectric effect. The presence of such particles induces charge of opposite polarity on a stationary conducting electrode. The amount of charge carried by the particles and the trajectories of the particles have significant random components and the signals produced are of very low level. The signal processing is further complicated by the random variation in the concentration of particles, i.e. the solid/gas ratio. This paper compares the results obtained from the electrostatic modelling of such sensors with those obtained from experiments.