Computational modelling and analysis of the flow and performance in hydrocyclones

Hydrocyclones have been widely used to separate particles by size in many industries. Their flows are complicated and involve multiple phases: liquid, gas, and particles of different sizes and densities. A two fluid model, facilitated with the mixture model, has been used to study the flow in hydrocyclones under wide range of conditions and used here to study the effects of geometrical configuration and material properties of cyclones operated at different feed solids concentrations. The variables considered include geometrical configurations such as dimensions and shape of body, cone and vortex finder as well as particle density. The outcome shows a smaller cyclone results in an increased cut size, decreased pressure drop, sharper separation and higher water split. Both large and small spigot diameters lead to poor separation performances. Accordingly, an optimum spigot diameter can be identified depending on feed solids concentration. It is also shown that for all considered hydrocyclones, a better separation performance can be achieved by the operation at lower feed solid concentration. Further research shows that cyclone performance is sensitive to both length and shape of conical section. A longer conical section leads to decreased inlet pressure drop, d50, and Ep, and an increased water split. When cone shape varies from concave to convex, a compromise optimum performance for the cyclone with a convex cone is observed with a minimum Ep and relatively small pressure drop and water split. A new hydrocyclone featured with a long convex cone is then proposed which can improve the performance of the conventional cyclone. The keycharacteristics of flow in a hydrocyclone are then investigated when vortex finder geometry including diameter length and shape varies. It has been shown that a compromise optimum performance can be identified with relatively small inlet pressure drop, Ep, and water split. Discussion is then extended to flow behaviour analysis under the effect of different density fractions. The origin of flow pattern and the motion of coal particles have been predicted and discussed. The effect of coal density variation on operational conditions and performance of the large diameter hydrocyclones are also studied in this work

Decision Support Systems

The current decision-making problems is more complex than it was in the past, prompting the need for decision support. Most real-world decision-making situations are subject to bounded rationality; whereby the technical and economic evaluation of all solution alternatives (branches) is bounded by the consideration of dominant subjective constraints. The early definition of DSS introduced it as a system that intended to support decision makers in semi-structured problems that could not be completely supported by algorithms. DSSs were planned to be an accessory for managers to expand their capabilities but not to replace them. Decision support systems could provide the means to complement decision makers by quantitatively supporting managerial decisions that could otherwise be based on personal intuition and experience. In addition to the traditional DSS characteristics (i.e., data and model orientation, interactivity), the inclusion of an intelligent knowledge base would be required to quantify the impacts of both technical (hard) and subjective (soft) constraints

Towards eco-flowable concrete production

Environmental concerns have increased due to the amount of unused/expired plastic medical waste generated in hospitals, laboratories, and other healthcare facilities, in addition to the fact that disposing of such wastes with extremely low degradation levels causes them to remain in the environment for extended periods of time. These issues have led researchers to develop more environmentally friendly alternatives for disposing of plastic medical waste in Australia. This study is an attempt to assess the impacts of using expired plastic syringes as fine aggregate on fresh and hardened characteristics of flowable concrete, which might provide a solution to environmental concerns. Six mixtures of flowable concrete with water-to-cement ratios of 0.38 were studied. It was found that using recycled aggregate in up to 20% can improve the workability and increase the V-funnel values of flowable concrete mixtures. However, using waste aggregates in more than 30% caused an inapt flowability. Adding waste aggregate at the 30%–50% replacement level led to a decrease in the L-box ratio. To verify the utility and the efficacy of this experiment, the connections between different rheological test measurements were also compared by implementing the Pearson correlation function. The mechanical properties of the mixes containing recycled aggregates were decreased at the age of seven days; however, at later ages, waste aggregates increased the strength at the 10%–30% replacement levels

Modelling the moisture effect on the rate of spread of fire in a leaf-like fuel element

In this study, the effect of fuel moisture content (FMC) on the pyrolysis, ignition, and rate of drying processes of a leaf-like fuel element is numerically investigated. To start the ignition, an upward hot airflow is placed under the leaf-like fuel source. The dry fuel was considered as cellulose. The current study is validated against published experimental data, using the time history of fuel mass loss measurement. The effect of FMC on the mass fraction of oxygen is also investigated. The transient solver of FireFOAM, which uses the Large Eddy Simulation (LES), is used to perform the numerical simulations. The results confirm that an increase in the amount of fuel moisture content leads to a decrease in the rate of spread of the fire and an increase in the drying process time. It is also found that during both drying and pyrolysis process, different parts of a selected fuel element have different temperatures. This is mainly due to the decrease of moisture concentration near the ignition point. Results showed that at t= 6.5 s the volumetric average temperature of the solid fuel for the case with FMC 26%, is 642 K while for FMC of 34%, this temperature is 605 K

Developed Brinkman Model into a Porous Collector for Solar Energy Applications with a Single-Phase Flow

In this paper, the effects of the fluid-thermal parameters of a porous medium with different values of porosity and permeability on the fluid flow, heat, and concentration parameters were investigated for solar energy applications. The characteristics of the boundary layer, velocity profiles, pressure drop, and thermal and high heat concentration distribution have been analyzed. A developed Brinkman equation for fluid flow and a power law model for thermal conductivity (considering the porosity and permeability factors) were calculated with constant solar heat flux. The numerical model was developed based on the finite element method by the LU algorithm using the MUMPS solver. The Brinkman equations were solved under steady and unsteady states for velocity, pressure, thermal, and concentration distribution effects, respectively. In a porous medium, the normalized temperature of the presented model had an acceptable agreement with the experimental data, with a maximum error of 3%. At constant permeability, by decreasing the porosity, the velocity profile was extended. This was mainly due to the presence of pores in the collector. With an accelerated flow, the maximum velocity of 2.5 m/s occurred at a porosity of 0.2. It was also found that in the porous collector, the Nusselt number increased where the maximum difference between the porous and the nonporous collectors occurred at the beginning of the collector, with a value of 32%, and the minimum difference was 27%. The results also indicate that in the porous collector, solar energy absorbance was higher and the heat transfer was improved. However, an increase in the pressure drop was noted in the porous collectors

Numerical Simulation of the Influence of Hydrogen Concentration on Detonation Diffraction Mechanism

In this study, the impact of hydrogen concentration on deflagration to detonation transition (DDT) and detonation diffraction mechanisms was investigated. The combustion chamber was an ENACCEF facility, with nine obstacles at a blockage ratio of 0.63 and three mixtures with hydrogen concentrations of 13%, 20%, and 30%. Detonation diffraction mechanisms were numerically investigated by a density-based solver of OpenFOAM CFD toolbox named ddtFoam. In this simulation, for the low Mach numbers, the pddtFoam solver was applied, and for high speeds, the pddtFoam solver switched to the ddtFoam solver to simulate flame propagation without resolving all microscopic details in the flow in the CFD grid, and to provide a basis for simulating flame acceleration (FA) and the onset of detonation in large three-dimensional geometries. The results showed that, for the lean H2–air mixture with 13% hydrogen concentration, intense interaction between propagating flame and turbulent flow led to a rapid transition from slow to fast deflagration. However, the onset of detonation did not occur inside the tube. For the H2–air mixture with 20% hydrogen concentration, the detonation initiation appeared in the acceleration tube. It was also found that following the diffraction of detonation, the collision of transverse waves with the wall of the tube and the reflection of transverse waves were the most essential and effective parameters in the re-initiation of the detonation. For the H2–air mixture with 30% hydrogen concentration, the detonation initiation occurred while passing through the obstacles. Subsequently, at detonation diffraction, the direct initiation mechanism was observed

Thermodynamic analysis of incineration treatment of waste disposable syringes in an EAF steelmaking process

Disposal of waste syringes in a safe and eco-friendly way has been an issue of considerable scale for decades. The generated amount of waste syringes has escalated with the rapid growth in population and wide acceptance towards single-use medical devices. Some hospitals have their own on-site incinerators, but recent tightening of air quality regulations and landfill levies led to the closure of many on-site incinerators. The solution to this problem implicates the development of an environmentally-sound method that would employ these waste materials. This work investigates a thermodynamic modelling approach for incineration treatment of waste plastic syringes in Electric Arc Furnace (EAF) steelmaking. Mass balance was obtained from HSC Chemistry thermochemical package. The results indicate that the rate of iron oxide reduction in the slag is higher when coke is partially replaced by waste plastic syringes. Furthermore, the amount of dust and stack gas emission was reduced by around 0.4% and 1.25% respectively by replacing 20%-weight of pure coke with waste plastic syringes. The study demonstrates part of the coke can be successfully replaced by waste plastic syringes in electric arc furnace to provide additional energy from combustion without affecting the main process

Techno-economic analysis of energy recovery from plastic waste

Treatment of polymer-based wastes has a tremendous potential for generating alternative energy, reducing greenhouse gas emissions, creating economic and environmental benefits, and achieving a sustainable development of the energy sector. During the past few decades, plastic waste generation increased at a greater rate than the population, with the move towards single-use products. Also with raising the cost of oil-based products, greater emphasis should be placed upon the usage of plastic/polymer in the waste stream as a supplementary source of fuel. This study presents a techno-economic analysis of the recycling potential of plastic waste in Australia by evaluating the possible use of these wastes as a reductant in steel making incinerators. The study tries to shed light on a possible cost effective alternative route in the smart treatment of waste plastic in Australia

Numerical Simulation of the Influence of Hydrogen Concentration on Detonation Diffraction Mechanism

In this study, the impact of hydrogen concentration on deflagration to detonation transition (DDT) and detonation diffraction mechanisms was investigated. The combustion chamber was an ENACCEF facility, with nine obstacles at a blockage ratio of 0.63 and three mixtures with hydrogen concentrations of 13%, 20%, and 30%. Detonation diffraction mechanisms were numerically investigated by a density-based solver of OpenFOAM CFD toolbox named ddtFoam. In this simulation, for the low Mach numbers, the pddtFoam solver was applied, and for high speeds, the pddtFoam solver switched to the ddtFoam solver to simulate flame propagation without resolving all microscopic details in the flow in the CFD grid, and to provide a basis for simulating flame acceleration (FA) and the onset of detonation in large three-dimensional geometries. The results showed that, for the lean H2–air mixture with 13% hydrogen concentration, intense interaction between propagating flame and turbulent flow led to a rapid transition from slow to fast deflagration. However, the onset of detonation did not occur inside the tube. For the H2–air mixture with 20% hydrogen concentration, the detonation initiation appeared in the acceleration tube. It was also found that following the diffraction of detonation, the collision of transverse waves with the wall of the tube and the reflection of transverse waves were the most essential and effective parameters in the re-initiation of the detonation. For the H2–air mixture with 30% hydrogen concentration, the detonation initiation occurred while passing through the obstacles. Subsequently, at detonation diffraction, the direct initiation mechanism was observed