CFD model simulation of bubble surface area flux in flotation column reactor in presence of minerals

Bubble surface area flux(S_b) is one of the main design parameter in flotation column that typically employed to describe the gas dispersion properties, and it has a strong correlation with the flotation rate constant. There is a limited information available in the literature regarding the effect of particle type,density, wettability and concentration on Sb. In this paper, computational fluid dynamics(CFD) simulations are performed to study the gas–liquid–solid three-phase flow dynamics in flotation column by employing the Eulerian–Eulerian formulation with k-e turbulence model. The model is developed by writing Fortran subroutine and incorporating then into the commercial CFD code AVL FIRE, v.2014.This paper studies the effects of superficial gas velocities and particle type, density, wettability and concentration on Sband bubble concentration in the flotation column. The model has been validated against published experimental data. It was found that the CFD model was able to predict, where the response variable as indicated by R-Square value of 0.98. These results suggest that the developed CFD model is reasonable to describe the flotation column reactor. From the CFD results, it is also found that Sb decreased with increasing solid concentration and hydrophobicity, but increased with increasing superficial gas velocity. For example, approximately 28% reduction in the surface area flux is observed when coal concentration is increased from 0 to 10%, by volume. While for the same solid concentration and gas flow rate, the bubble surface area flux is approximately increased by 7% in the presences of sphalerite.A possible explanation for this might be that increasing solid concentration and hydrophobicity promotes the bubble coalescence rate leading to the increase in bubble size. Also, it was found that the bubble concentration would decrease with addition of hydrophobic particle(i.e., coal). For instance, under the same operating conditions, approximately 23% reduction in the bubble concentration is predicted when the system was working with hydrophobic particles. The results presented are useful for understanding flow dynamics of three-phase system and provide a basis for further development of CFD model for flotation column.

Additively manufactured fiber-reinforced composites:A review of mechanical behavior and opportunities

Recent developments in additive manufacturing techniques have facilitated the fabrication of fiberreinforced composite materials.In this paper,the mechanical properties and deformation mechanisms of discontinuous and continuous fiber-reinforced composites fabricated by various additive manufacturing techniques are comprehensively reviewed.The effects of fiber type,orientation and weight/volume fraction,printing path,and stacking sequence on the mechanical properties of additively manufactured composites are discussed.In addition,the applications of additively manufactured composites,the main challenges of the current additive manufacturing techniques,and recommendations for future work are also presented.

Modeling, analysis, and optimization of dimensional accuracy of FDM-fabricated parts using definitive screening design and deep learning feedforward artificial neural network

Additive manufacturing(AM)technologies such as fused deposition modeling(FDM)rely on the quality of manufactured products and the process capability.Currently,the dimensional accuracy and stability of any AM process is essential for ensuring that customer specifications are satisfied at the highest standard,and variations are controlled without significantly affecting the functioning of processes,machines,and product structures.This study aims to investigate the effects of FDM fabrication conditions on the dimensional accuracy of cylindrical parts.In this study,a new class of experimental design techniques for integrated second-order definitive screening design(DSD)and an artificial neural network(ANN)are proposed for designing experiments to evaluate and predict the effects of six important operating variables.By determining the optimum fabrication conditions to obtain better dimensional accuracies for cylindrical parts,the time consumption and number of complex experiments are reduced considerably in this study.The optimum fabrication conditions generated through a second-order DSD are verified with experimental measurements.The results indicate that the slice thickness,part print direction,and number of perimeters significantly affect the percentage of length difference,whereas the percentage of diameter difference is significantly affected by the raster-to-raster air gap,bead width,number of perimeters,and part print direction.Furthermore,the results demonstrate that a second-order DSD integrated with an ANN is a more attractive and promising methodology for AM applications.

Deposition processes and properties of coatings on steel fasteners——A review

Mechanical fastening is widely used in joining metals, particularly in automotive, aerospace, building and construction industries. However, the main concern on mechanical fastening is the issue of corrosion. An effective way to prolong the service life of steel fasteners is to apply protective coatings onto these components. This paper reviews and compares a few common coating deposition techniques, i.e., electroplating, hot-dip galvanizing, ion vapour deposition and mechanical plating, in terms of their characteristics. Compositional and microstructural properties including morphology and porosity, corrosion resistance performance and frictional performance of the coatings formed by each process are discussed in details. Hydrogen embrittlement, a premature failure often occurred on high strength steel fasteners, is also reviewed. The key results of recent studies of various metallic coatings on fasteners are presented to provide a fundamental understanding of the evolving topics, and the research gaps have been identified for further investigation.

Effects of particle size and concentration on bubble coalescence and froth formation in a slurry bubble column

A new approach for simulating the formation of a froth layer in a slurry bubble column is proposed. Froth is considered a separate phase, comprised of a mixture of gas, liquid, and solid. The simulation was carried out using commercial flow simulation software （FIRE v2014） for particle sizes of 60-150 μm at solid concentrations of 0-40vol%, and superficial gas velocities of 0.02-0.034m/s in a slurry bubble column with a hydraulic diameter of 0.2 m and height of 1.2 m. Modelling calculations were conducted using a Eulerian-Eulerian multiphase approach with k-ε turbulence. The population balance equations for bubble breakup, bubble coalescence rate, and the interfacial exchange of mass and momentum were included in the computational fluid dynamics code by writing subroutines in Fortran to track the number density of different bubble sizes. Flow structure, radial gas holdup, and Sauter mean bubble diameter distributions at different column heights were predicted in the pulp zone, while froth volume fraction and density were predicted in the froth zone. The model was validated using available experimental data, and the predicted and experimental results showed reasonable agreement. To demonstrate the effect of increasing solid concentration on the coalescence rate, a solid-effect multiplier in the coalescence effi- ciency equation was used. The solid-effect multiplier decreased with increasing slurry concentration, causing an increase in bubble coalescence efficiency. A slight decrease in the coalescence efficiency was also observed owing to increasing particle size, which led to a decrease in Sauter mean bubble diam- eter. The froth volume fraction increased with solid concentration. These results provide an improved understanding of the dynamics of slurry bubble reactors in the presence of hydrophilic particles.

Optimization of fused deposition modeling process parameters:a review of current research and future prospects

Fused deposition modeling （FDM） is one of the most popuIar additive manufacturing technologies for various engineering applications. FDM process has been introduced commercially in early 1990s by Stratasys Inc., USA. The quality of FDM processed parts mainly depends on careful selection of process variables. Thus, identifica- tion of the FDM process parameters that significantly affect the quality of FDM processed parts is important. In recent years, researchers have explored a number of ways to improve the mechanical properties and part quality using various experimental design techniques and concepts. This article aims to review the research carried out so far in determining and optimizing the process parameters of the FDM process. Several statistical designs of experiments and optimization techniques used for the determination of optimum process parameters have been examined. The trends for future FDM research in this area are described.

Dynamic compressive behaviour of Ti-6Al-4V alloy processed by electron beam melting under high strain rate loading

This paper documents an investigation into the compressive deformation behaviour of electron beam melting （EBM） processing titanium alloy （Ti-6A1-4V） parts under high strain loading conditions. The dynamic compression tests were carried out at a high strain rate of over 1 × 10^3/S using the split Hopkinson pressure bar （SHPB） test system and for comparison the quasi-static tests were performed at a low strain rate of 1×10^-3/s using a numerically controlled hydraulic materials test system （MTS） testing machine at an ambient temperature. Furthermore, microstructure analysis was carried out to study the failure mechanisms on the deformed samples. The Vickers micro-hardness values of the samples were measured before and after the compression tests. The microstructures of the compressed samples were also characterized using optical microscopy. The particle size distribution and chemical composition of powder material, which might affect the mechanical properties of the specimens, were investigated. In addition, the numerical simulation using commercial explicit finite element software was employed to verify the experimental results from SHPB test system.

Nickel-titanium shape memory alloys made by selective laser melting:a review on process optimisation

Selective laser melting(SLM)is a mainstream powder-bed fusion additive manufacturing(AM)process that creates a three-dimensional(3D)object using a high power laser to fuse fine particles of various metallic powders such as copper,tool steel,cobalt chrome,titanium,tungsten,aluminium and stainless steel.Over the past decade,SLM has received significant attention due to its capability in producing dense parts with superior mechanical properties.As a premier shape memory alloy,the nickel-titanium(NiTi)shape memory alloy is attractive for a variety of biomedical applications due to its superior mechanical properties,superelasticity,corrosion resistance and biocompatibility.This paper presents a comprehensive review of the recent progress in NiTi alloys produced by the SLM process,with a particular focus on the relationship between processing parameters,resultant microstructures and properties.Current research gaps,challenges and suggestions for future research are also addressed.

General heat balance for oxygen steelmaking

Energy balances are a general fundamental approach for analyzing the heat requirements for metallurgical processes.The formulation of heat balance equations was involved by computing the various components of heat going in and coming out of the oxygen steelmaking furnace.The developed model was validated against the calculations of Healy and McBride.The overall heat losses that have not been analyzed in previous studies were quantified by back-calculating heat loss from 35 industrial data provided by Tata Steel.The results from the model infer that the heat losses range from 1.3%to 5.9%of the total heat input and it can be controlled by optimizing the silicon in hot metal,the amount of scrap added and the postcombustion ratio.The model prediction shows that sensible heat available from the hot metal accounts for around 66%of total heat input and the rest from the exothermic oxidation reactions.Out of 34%of the heat from exothermic reactions,between 20%and 25%of heat is evolved from the oxidation of carbon to carbon monoxide and carbon dioxide.This model can be applied to predict the heat balance of any top blown oxygen steelmaking technology but needs further validation for a range of oxygen steelmaking operations and conditions.