A review on aluminothermic reaction of Al/ZnO system

Aluminothermic reaction between aluminum and a metallic oxide is worth noting, because it is applicable in some applications such as in-situ aluminum/alumina composites synthesis, welding, etc. All the metallic oxides with Gibbs free energy of formation higher than Al₂O₃ can be used as the reactant oxide. Among them, the aluminothermic reaction between Al and ZnO is thermodynamically possible, because its free energy change is negative, even at room temperature. Depending on the processing method, part of the reduced Zn can be vaporized during the procedure, while the rest remains in the Al matrix. This paper attempts to review the published research works on Al/ZnO aluminothermic reaction by different processing routes giving an overview of the reactions in the liquid and solid state processes. Highlighting the technical barriers against the aluminothermic reaction propagation in Al/ZnO system, discussing the effects of different approaches on the ignition temperature as well as demonstrating how the reaction is kinetically possible even at ambient temperature are the main aspects of the present review paper. Moreover, the mechanism of the reaction and microstructural properties of the products are discussed in details. It was shown that aluminothermic reaction in the liquid state processes might be hindered kinetically due to poor wettability between aluminum and zinc oxide particles. Moreover, the results revealed that the combined mechanical and thermal treatments and mechanochemical methods facilitate the aluminothermic reaction compared to exothermic dispersion (XD). Changing the diffusion mode from bulk diffusion to grain boundary diffusion was considered as the main reason.     

Heat Transfer Analysis of a Microspherical Particle in the Slip Flow Regime by Considering Variable Properties

In order to investigate how far the temperature-dependent fluid properties and characteristic length influence the drag coefficient and the heat flux, a three-dimensional simulation study for a slip flow around an unconfined microspherical particle has been performed. Gas properties such as density, viscosity, conductivity, and mean free path were assumed to vary with temperature. Slip velocity and temperature jump at the gas particle interface were both treated numerically by imposition of the slip boundary conditions. The effects of variable gas properties and Knudsen number on momentum and heat transfer were also taken into account. It was concluded that for microflows with high heat transfer rates, the constant fluid properties approximation is very crude. In addition, the slip velocity and temperature jump affect the heat transfer in opposite ways: a large slip on the wall increases the convection along the surface, whereas a large temperature jump decreases the heat transfer by reducing the temperature gradient at the wall. Therefore, neglecting temperature jump will result in the overestimation of the heat transfer coefficient.     

Water detection framework for industrial electric arc furnaces: Boundary modelling and formulation

This paper describes the development of a boundary model for the off-gas water vapour in an industrial steelmaking electric arc furnace (EAF). The solution addresses the mechanistic components of a complete EAF water detection framework. The boundary model has been implemented on an industrial alternating current (AC) EAF. The model specifies upper and lower limits in real-time of the expected EAF off-gas water vapour leaving the furnace, and it provides a valuable on-line monitoring tool to the operator on what boundary to expect for the off-gas water vapour in different circumstances. An essential data required for the framework is the EAF off-gas composition. So, in this work, an off-gas analyzer with a human machine interface (HMI) and a supervisory control and data acquisition (SCADA) system was installed in the first step. Then, in order to evaluate the developed water leak detection framework and verify the obtained results, industrial trials were designed in which a certain amount of water was intentionally added into the furnace by increasing the electrode spray water flow rate. Moreover, we have shown how the presented framework can be used to appropriately adjust the alarm setting values in control/emergency shutdown systems of industrial EAF to enhance the safety and availability of the plant.     

Heat Transfer Enhancement Using Rectangular and Triangular Shaped Baffles with and without Nanofluid: New Insight into Optimization of Flow Geometric Parameters

Protection of Metals and Physical Chemistry of Surfaces - In this paper, the optimization of geometric parameters that affect heat transfer and pressure drop of water-Al2O3 nanofluid were carried...     

Elimination of solidification shrinkage defects in the casting of aluminum alloy

Journal of Mechanical Science and Technology - In this study, the analysis is carried out to optimize in-gate position and size of riser for casting mold. The baseline size of riser for the casting...     

Ballistic Ejection of Microdroplets from Overpacked Interfacial Assemblies

Spontaneous emulsification, resulting from the assembly and accumulation of surfactants at liquid–liquid interfaces, is an interfacial instability where microdroplets are generated and diffusively spread from the interface until complete emulsification. Here, it is shown that an external magnetic field can modulate the assembly of paramagnetic nanoparticle surfactants (NPSs) at liquid–liquid interfaces to trigger an oversaturation in the areal density of the NPSs at the interface, as evidenced by a marked reduction in the interfacial tension, γ, and corroborated with a magnetostatic continuum theory. Despite the significant reduction in γ, the presence of the magnetic field does not cause stable interfaces to become unstable. Upon rapid removal of the field, however, an explosive ejection of a plume of microdroplets from the surface occurs, a dynamical interfacial instability which is termed explosive emulsification. This explosive event rapidly reduces the areal density of the NPSs to its pre-field level, stabilizing the interface. The ability to externally suppress or trigger the explosive emulsification and controlled generation of tens of thousands of microdroplets, uncovers an efficient energy storage and release process, that has potential applications for controlled and directed delivery of chemicals and remotely controlled soft microrobots, taking advantage of the ferromagnetic nature of the microdroplets.     

Keys to improve the efficiency of nanoparticle-stabilized foam injection based on influential mechanisms

The effect of the existence of nanoparticles on foam stability, foamability, and the oil recovery factor (RF) has been studied experimentally, and influential phenomena and mechanisms have been examined. A sequence of experiments, including, ‘foam bulk-static experiments’, ‘surface tension (ST) measurements,’ and ‘micromodel foam flood,’ were designed and then implemented to study the foam behaviour in two foam systems: (1) anionic-nanoparticles + cationic-surfactant and (2) anionic-nanoparticles + anionic-surfactant. This study provides a comprehensive insight into the mechanisms affecting the stability of nanoparticle-stabilized foam. Also, despite previous studies, the effect of Marangoni flow on nanoparticle-stabilized foam has been discussed briefly. Results show that the interactions of effective mechanisms work differently in the two series. In the like-charge system, surfactant molecules accumulate in the interface of lamellas due to repulsive forces; therefore, stability and foamability improve as surface tension and molecular diffusion reduce. Additionally, Marangoni flow restitutes the negative impact of gravity drainage. In the unlike-charge system, observations illustrate that nanoparticles reach the interface. The presence of nanoparticles at the interface increases detachment energy significantly, and as a result, the stability is boosted. The accumulation of nanoparticles in the interface changes it to a solid-like surface with limited diffusibility and viscosity. Although Marangoni flow is lost, reducing molecular diffusion improves foam stability. Flooding tests show that foam stability increment improves sweep efficiency at near-wellbore areas even when foamability is weak. Finally, it can be claimed that in the unlike-charge system, the sweep efficiency and foam stability increase to a greater extent.