Parametric study of mini-axial flow hydrocyclone through numerical simulation

This research article encompasses the parametric analysis of axial flow hydrocyclone with suitably designed numerical experiments at various operating conditions. The effect of inlet dimensions, vortex finder length, and vortex finder diameter on the performance and flow pattern has been computationally investigated using large eddy simulation (LES) for twelve hydrocyclone separators altogether. The result shows that the maximum tangential velocity and axial velocity profiles in the hydrocyclone decreases with increasing inlet dimensions, vortex finder length and diameter. A similar trend is found for turbulence fluctuation in tangential and axial directions, vorticity and helicity. Power spectral density is analysed to check the distribution of velocity fluctuation (Vin=2m/s) over the frequency component, and the results show the PSD magnitude is almost the same for the geometric parameter variations, which peaked at 105 Hz. To examine the effect on the performance of hydrocyclone, the separation efficiency, cut size (d50), sharpness of separation and pressure drop were evaluated. The separation efficiency of smaller diameter vortex finders is higher for the large particles than that of wider ones at the cost of high-pressure drop. Numerical results also show that prolonging the vortex finder length increases the separation efficiency, decreasing the cut size due to weakness of vortex strength. It elucidates a critical length for the vortex finder. According to the results, changing the vortex finder diameter and length is more significant than the inlet dimensions, especially for velocity profiles. This study also analyses the identification of vortex (iso-vortex surface) and decay through Q-criterion, which helps understand the vortex formation of hydrocyclone separator

Acid mist formation in the electrowinning of copper

The formation of acid mist in the electrowinning of copper can result in a health hazard if the concentrations of the acid mist is too high. A study was carried out in a model electrowinning bath where the gas generation in an electrowinning bath was simulated by controlled gas injection. The breakup of the bubbles at the free surface controlled the mechanism for acid mist formation. The results showed that the bubble size and concentration played an important part in determining the droplet size and density that formed the acid mist. The amount of acid mist formed for different bubble concentration showed that the acid mist concentration above a model of the electrowinning bath decreases exponentially with distance from the bath surface. However, fine bubbles resulted in fine acid mist gives rise to droplets that can be carried away by the gas generated. The study identified means of reducing the acid mist concentration without the need to install complex gas cleaning and isolation equipment

Sloshing of melts in a bath smelting process having a elliptic cross section

Recently, the use of the elliptic cross section cylinder for bath smelting operations was adopted by the Ausiron process. The high gas flow rates used have been found to generate wave motion in the bath that can enhance refractory wear. The standing wave modes were found for the bath. Two distinct sets of eigenvalues were obtained, one in the major axis and the other in the minor axis. The two sets converged when the ellipticity of the cylinder is zero, which is the shape of a circle. The calculated wave frequency was found to agree well with experimental data. A complete set of eigenvalues have been calculated for elliptic cylinders and fitted to Chebyshev polynomials, enabling quick estimation of the standing wave frequencies. The study showed that the ellipticity of the vessel for the Auslron process needs to be carefully chosen as the standing wave modes that can be generated may result in beat frequencies that can interact with the natural frequencies of the vessel support and auxilliary equipment

Numerical modelling of free surface flows in metallurgical vessels

A numerical model for simulating the transient behaviour of multi-fluid problems defined in 2D rectangular and cylindrical geometries is presented. The model uses a piecewise linear volume tracking scheme, and maintains sharp interfaces and captures fine-scale flow phenomena such as fragmentation and coalescence. The numerical model was applied to four problems of pyrometallurgical relevance - entrainment of matte in the flow of slag during skimming operations, splash resulting from a drop impinging on a bath, bubble rise in a liquid bath, and top-submerged gas injection. The numerical predictions are in good agreement with the published experimental results. The simulation of top-submerged gas injection showed, in detail, the phenomena of bubble formation, bubble rise, and splash drop formation and recoalescence with the bath. Data useful for engineering purposes such as pressure traces and time-averaged flow fields were obtained, allowing assessment of splash behaviour for given gas injection conditions. The numerical model has been shown to be versatile in being able to adapt to a wide range of multi-phase flow problems

CFD model development for sugar mill evaporators

A numerical model is presented for the single-phase fluid\ud flow inside a sugar mill evaporator vessel. The model\ud incorporates the effect of temperature and sugar\ud concentration on the fluid properties. The model is a\ud quarter wedge of the evaporator where the vertical heating\ud tubes III the calandria section are modelled through a\ud momentum source term in three directions. Although the\ud use of the momentum source term in the calandria section\ud did not result in fluid flow being completely restricted to\ud the vertical direction, the predictions show reasonable\ud agreement when compared with measurements taken from\ud the actual vessel. The model presented here is capable of\ud predicting trends in the fluid flow behaviour for\ud processing conditions normally experienced in the final\ud vessel of a multiple-effect evaporator set. The predictions\ud show that the design of the juice distribution system at the\ud inlet to the vessel has a major influence on the flow field\ud in the remainder of the vessel. A large amount of mixing\ud was found to occur at the inlet resulting in the calandria\ud region being exposed to juice with properties close to the\ud outlet stream, which is detrimental to performance

Effect of wood/binder ratio, slag/binder ratio, and alkaline dosage on the compressive strength of wood-geopolymer composites

The impact of building construction on the environment is significant. Occupying large land areas (urban footprint), buildings are one of the most important consumers of resources and raw materials. They are responsible for 38% of greenhouse gas (GHG) emissions in both developed and developing countries. Therefore, incorporating sustainability and resilience into all aspects of urban infrastructure has become necessary. To curb emissions, part of the answer lies in the use of construction and building materials made from recycled materials. Bio-sourced materials, like wood chips, combined with a cementitious matrix, offer an alternative to conventional materials. They are sustainable, lightweight, and have good thermal insulation. However, because of their inferior mechanical strength, they have limited use as load-bearing structural parts. Furthermore, the use of Portland cement as a binder still poses some challenges due to its high carbon footprint. This study investigates the potential of wood-geopolymer composites for better mechanical performance and environmental sustainability. A 6x2x2x2 fractional factorial-based experimental design was used to simultaneously study the effect of slag content, wood binder ratio, and alkaline on the compressive strength of the wood-geopolymer composite. The experiments showed encouraging results for developing ambient cured wood geopolymer composites. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG

Recycling timber waste into geopolymer cement bonded wood composites

Addressing critical societal challenges, such as climate change, resource depletion, and environmental protection, requires sustainable management of resources. This study reports on the results of an experimental program using waste wood, including chromium copper arsenic (CCA) treated wood, to produce ambiently cured geopolymer cement bonded wood composites (WGC), and the results are very encouraging. The composite exhibited a reasonable compressive strength, which ranged between 7 and 27 MPa inversely corresponding to the amount of wood per binder ratio ranging between 0.1 and 0.4, conferring it the possibility of being used as a building material. The compressive strength of the composite with 40% wood chips showed the lowest compressive strength with values of 9.79, 7.29, and 7.92 MPa for decontaminated, CCA-treated, and non-CCA-treated wood chips, respectively. The results indicated that for all the wood per binder ratios, the use of decontaminated wood chips significantly improves the compressive, flexural, and specific strength of the composites, as well as their ductility, compared to non-decontaminated CCA-treated and non-CCA-treated wood chips. This paves the way for using wood waste in sustainability oriented product development and manufacturing. © 2023 The Author(s

A 3D unsplit-advection volume tracking algorithm with planarity-preserving interface reconstruction

A new volume tracking method is introduced for tracking interfaces in three-dimensional (3D) geometries partitioned with orthogonal hexahedra. The method approximates interface geometries as piecewise planar, and advects volumes in a single unsplit step using fully multidimensional fluxes that have their definition based in backward-trajectory remapping. By using multidimensional unsplit advection, the expense of high-order interface reconstruction is incurred only once per timestep. Simple departures from strict backward-trajectory remapping remove any need for consideration of volume computations involving shapes consisting of non-planar ruled surfaces. Second-order accuracy of the method is demonstrated even for vigorous 3D deformations