CFD modelling and simulation of industrial-scale copper electrorefining process

Both electrolyte flow and cupric ion concentration fields have been numerically calculated with the computational fluid dynamics (CFD) model in an industrial-scale copper electrorefining cell. In this CFD model, both of the natural convection induced by the electrochemical reactions and the forced convection caused by the electrolyte circulation are taken into account. In order to examine how the difference in the ways of the electrolyte circulation affects the electrolyte flow pattern associated with the concentration field, three different ways of the electrolyte circulation, “bottom inlet to top outlet”, “top inlet to bottom outlet”, and “side inlet to top outlet”, have been modeled.Calculation results have revealed that both “bottom inlet to top outlet” and “top inlet to bottom outlet” circulations have characteristic flow patterns that are locally formed near the inlet. On the other hand, “side inlet to top outlet” circulation forms the inherent two vortex tubes in the space below the electrodes. It is also found that the electrolyte flow patterns in the inter-electrode spaces are formed mainly by the natural convection, and they are insensitive to kinds of the electrolyte circulation way.     

Estimation of platinum flotation grades from froth image data

Features extracted online from froth images on flotation plants are potentially useful to the development of advanced control for flotation systems, provided that these features can be related to the key indicator variables of the plant, such as valuable metal loadings and recovery. Although such relationships have been established in a number of base metal plants in industry, this is not the case in the platinum industry. In this paper, estimation of flotation grades and recoveries from froth image data is therefore considered based on laboratory and industrial plant data. It is shown that grades and recoveries can be reliably estimated from a number of different features by use of linear and nonlinear models. This includes simple colour information that on the industrial plant showed a strong correlation with grade measurement.     

The effect of stirring speed and induction time on flotation

A computational fluid dynamic model has been developed for a modified Denver flotation cell used in laboratory batch tests. The model incorporates fundamental aspects of bubble-particle interactions including bubble-particle collision, attachment and detachment. Model predictions are compared against carefully planned laboratory experiments with narrowly-sized spherical ballotini. Flotation results for different impeller speeds have been obtained for a constant air flow into the cell. The particles have been made hydrophobic by methylation with trimethylchlorosilane. For a given particle size, the results from the model and experimental work indicate that there is an optimum stirring speed that produces a good compromise between attachment and detachment rates in the cell for flotation. For less hydrophobic particles, a lower stirring speed is beneficial in having a longer contact time because of the longer induction time required for attachment.     

The development of low volatile organic compound emission house—a case study

An aim in developing low volatile organic compound (VOCs) emission house is to reduce the level of VOCs in domestic housing. In this study, a case study for the reduction of exposure to VOCs from a newly constructed residential house was presented. Before application, the construction materials used in the house were tested in an environmental chamber and low VOC emission materials were then selected. Design of the house abided by the following principals: maximizing the ventilation rate and avoiding the use of high VOC emission materials in the house. By improved building design and proper construction materials selection, risk of personal exposure to VOCs in the house was significantly reduced. The total VOCs (TVOCs) concentrations measured in the house ranged from non-detectable to 43 μg/m³. These values were much lower than the published values (0.48–31.7 mg/m³) for new houses in Scandinavian countries and in the USA. The low TVOCs concentrations obtained in this study probably resulted from the high ventilation rates and the use of low VOCs emission materials. This study also combined the results with the three traditional ways in improvement of IAQ. The results obtained in this study confirmed that the most effective strategy for controlling IAQ was pollution prevention and the next most important was the design of ventilation rates to handle uncontrollable sources. The effectiveness of aging as a means of indoor pollution control was also reviewed.     

Heating,ventilation and air conditioning system modelling

Heating, ventilation and air conditioning modelling methods, for large scale, spatially dispersed systems are considered. Existing techniques are discussed and proposals for the application of novel analysis approaches are outlined. The use of distributed–lumped parameter procedures enabling the incorporation of the relatively concentrated and significantly dispersed, system element characteristics, is advocated. A dynamic model for a heating, ventilation and air conditioning system comprising inlet and exhaust fans, with air recirculation, heating/cooling and filtration units is presented. Pressure, airflow and temperature predictions within the system are computed following input, disturbance changes and purging operations. The generalised modelling advancements adopted and the applicability of the model for heating, ventilation and air conditioning system simulation, re-configuration and diagnostics is emphasised. The employment of the model for automatic, multivariable controller design purposes is commented upon.     

An integrated approach for tactical monitoring and data-driven spread forecasting of wildfires

In recent times there have been increasing efforts to integrate technology into wildfire management, especially in the fields of tactical monitoring and simulation. On the one hand, thermal infrared imaging (TIR) systems have been installed aboard surveillance aircraft including unmanned systems (UAS). On the other, there exists a variety of models and simulators able to forecast the fire spread. However, both fields currently present significant limitations. While relevant information is still extracted manually from aerial thermal imagery and is most times merely qualitative, simulators’ accuracy on fire spread prediction has proved insufficient. To solve these issues, this article presents a twofold methodology to couple meaningful automated wildfire monitoring with accurate fire spread forecasting. The main goals are to, firstly, automatically process aerial TIR imagery so that valuable information can be produced in real time during the event and, secondly, use this information to adjust a Rothermel-based simulator in order to improve its accuracy on-line. The fire perimeter location is tracked automatically through an unsupervised edge detector. Afterwards, an assimilation module uses the remotely sensed data to optimise the simulator's fuel and wind parameters, which are assumed to remain constant for a certain period of time. Subsequently, the optimum parameters’ values are used to issue a fire evolution forecast. All outputs are projected onto the corresponding Digital Terrain Model (DTM) and integrated into a Geographic Information System (GIS) for visualization. The global system was validated using two large-scale experiments. If these algorithms can be applied to a sufficiently rich and varied set of experimental data and further developed to cope with more complex scenarios, they could eventually be incorporated into a fire management decision support system.     

Performance of axially restrained concrete encased steel composite columns at elevated temperatures

The structural performance of axially restrained concrete encased steel composite columns at elevated temperatures is investigated in this study. An efficient nonlinear 3-D finite element model was presented for the analysis of the pin-ended axially loaded columns. The restraint ratios varied from 20% to 100% of the axial stiffness of the composite columns at ambient temperature. The finite element model was verified against published test results on axially restrained concrete encased steel composite columns at elevated temperatures. The columns investigated had different cross-sectional dimensions, different coarse aggregates and different load ratios during fire. The nonlinear material properties of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement at ambient and elevated temperatures were considered in the finite element model. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the column. The initial overall geometric imperfection was carefully included in the model. The time-temperature relationships, deformed shapes at failure, time-axial displacement relationships, failure modes and fire resistances of the columns were evaluated by the finite element model and compared well against test results. Furthermore, the variables that influence the fire resistance and behaviour of the axially restrained composite columns comprising different axial restraint ratios, different load ratios during fire, different coarse aggregates and different slenderness ratios were investigated in a parametric study. It is shown that axially restrained composite columns behave differently in fire compared to the unrestrained columns since the typical “runaway” failure was not predicted from the finite element analysis. The fire resistances of the composite columns obtained from the finite element analysis were compared with the design values obtained from the Eurocode 4 for composite columns at elevated temperatures. It is shown that the EC4 is generally conservative for all the axially restrained concrete encased steel composite columns, except for some columns with higher load and slenderness ratios.     

Incorporation of inorganic material in anoxic/aerobic-activated sludge system mixed liquor

In the bioreactor of the nitrification denitrification (ND)-activated sludge system, the mixed liquor is made up of organic and inorganic materials. In the current design procedures and simulation models, the influent wastewater characteristics and biological processes that influence the bioreactor mixed liquor organic solids (as volatile suspended solids, VSS, or COD) are explicitly included. However, the mixed liquor total suspended solids (TSS, i.e. organic+inorganic solids) are calculated simply from empirical ratios of VSS/TSS. The TSS concentration is fundamental in the design of secondary settling tanks and waste activated sludge disposal. Clearly, the empirical approach to obtaining an estimate for TSS is not satisfactory within the framework of a fundamentally based model. Accordingly, the incorporation of the inorganic material present in the influent wastewater into ND-activated sludge system mixed liquor was investigated. From an experimental investigation into the distribution of inorganics in the influent, mixed liquor and effluent of a laboratory-scale ND-activated sludge system, it was concluded inter alia that (i) of the total inorganic solids in the influent, only a small fraction (2.8–7.5%) is incorporated into the mixed liquor, (ii) most of the inorganics in the influent (mean 88%) and effluent (mean 98.5%) are in the dissolved form, the balance being particulate, and (iii) the influent and effluent inorganic dissolved solids concentrations are closely equal (mean effluent to influent ratio 100%). Further, a number of models were developed to quantify the mixed liquor inorganic, and, hence, total solids. From an evaluation of these models against the experimental data, it would appear that the best approach to model the incorporation of inorganics into the activated sludge mixed liquor is to follow the concepts and principles used to develop the existing models for organic materials. With this approach, reasonably close correlation between predicted and measured data for mixed liquor and effluent inorganic concentrations were obtained.     

Ratcheting behaviour of elasto-plastic thin-walled pipes under internal pressure and subjected to cyclic axial loading

The present paper is concerned with the analysis of the ratcheting behaviour of elasto-plastic thin-walled pipes under internal pressure and subjected to cyclic axial loading. Understanding the behaviour of this kind of structure at different load levels is of critical importance in a range of engineering applications such as in the design of structural components of power and chemical reactors. Depending on the kinematic hardening, the pipe may exhibit a ratcheting behaviour in the circumferential direction, which leads to a progressive accumulation of deformation. Many different constitutive theories have been proposed to model the kinematic hardening under such kind of loading history. The present paper presents a simple local criterion to indicate whether or not the pipe may exhibit a progressive accumulation of deformation. Such criterion is independent of the choice of the evolution law adopted for the backstress tensor. As an example, a semi-analytic approach using a mixed nonlinear kinematic/isotropic hardening model is proposed to be used in a preliminary analysis of this kind of structure.     

Eccentrically loaded concrete encased steel composite columns

This paper presents a nonlinear 3-D finite element model for eccentrically loaded concrete encased steel composite columns. The columns were pin-ended subjected to an eccentric load acting along the major axis, with eccentricity varied from 0.125 to 0.375 of the overall depth (D) of the column sections. The model accounted for the inelastic behaviour of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement of the concrete encased steel composite columns. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the column. The initial overall geometric imperfection was carefully incorporated in the model. The finite element model has been validated against existing test results. The concrete strengths varied from normal to high strength (30–110 MPa). The steel section yield stresses also varied from normal to high strength (275–690 MPa). Furthermore, the variables that influence the eccentrically loaded composite column behaviour and strength comprising different eccentricities, different column dimensions, different structural steel sizes, different concrete strengths, and different structural steel yield stresses were investigated in a parametric study. Generally, it is shown that the effect on the composite column strength owing to the increase in structural steel yield stress is significant for eccentrically loaded columns with small eccentricity of 0.125D. On the other hand, for columns with higher eccentricity 0.375D, the effect on the composite column strength due to the increase in structural steel yield stress is significant for columns with concrete strengths lower than 70 MPa. The strength of composite columns obtained from the finite element analysis were compared with the design strengths calculated using the Eurocode 4 for composite columns. Generally, it is shown that the EC4 accurately predicted the eccentrically loaded composite columns, while overestimated the moment.