Summary
Acute pulmonary oedema in pregnant women is an uncommon but life‐threatening event. The aims of this review are to address why pulmonary oedema occurs in pregnant women and to discuss ...immediate management. We performed a systematic literature search of electronic databases including MEDLINE, EMBASE and the Cochrane Library, using the key words obstetrics, pregnancy, acute pulmonary oedema, pregnancy complications, maternal, cardiac function and haemodynamics. We present a simple clinical classification of acute pulmonary oedema in pregnancy into pulmonary oedema occurring in normotensive or hypotensive women (i.e. without hypertension), and acute pulmonary oedema occurring in hypertensive women, which allows focused management. Pre‐eclampsia remains an important cause of hypertensive acute pulmonary oedema in pregnancy and preventive strategies include close clinical monitoring and restricted fluid administration. Immediate management of acute pulmonary oedema includes oxygenation, ventilation and circulation control with venodilators. Pregnancy‐specific issues include consideration of the physiological changes of pregnancy, the risk of aspiration and difficult airway, reduced respiratory and metabolic reserve, avoidance of aortocaval compression and delivery of the fetus.
As the expectations for more consistent and higher density thickened and paste tailings in the minerals industry increase, so do the demands on flocculation performance within gravity thickeners. Low ...solids feed suspensions are delivered at a high velocity to center feedwells, which not only serve to dissipate the feed's momentum and evenly distribute the solids, but are also the primary means by which polymer flocculant solutions are distributed across the fine particle to form fast settling (but fragile) aggregates. Computational fluid dynamics (CFD) is a powerful tool for optimizing the design and performance of unit operations used to achieve particle aggregation and sedimentation. Early CFD feedwell modeling gave predictions on the solids and fluid flows, which were useful for identifying discharge asymmetry and short-circuiting currents, but did not give major insights into aggregation states. Incorporating a population balance (PB) model of aggregate growth and breakage made it possible to capture the critical impacts of shear, residence time and solids concentration that characterize polymer-bridging flocculation, in particular the potential for prolonged higher shear conditions to give excessive breakage. This created a unique capability for understanding the complex balance between the hydrodynamic and physical chemistry requirements for flocculation, enabling systematic CFD studies of different design and operation elements. Some of the main conclusions on feedwell design optimization are outlined. Potential future applications of CFD outputs in feed-forward thickener control are also discussed.
A CFD (computational fluid dynamics) model of a solvent extraction pulsed column has been developed and run with a single water phase. The results are compared with experimental measurements taken on ...a pilot scale column using PIV (particle image velocimetry).
The pulsed column investigated had disk–doughnut internals and was operated under pulsing intensities ranging from 10 to 32.5
mm/s. PIV measurements of velocity were used to validate the CFD model and to characterise the pulsing flow of a single phase through the column. The CFD modelling was performed for the same geometry and operating conditions using a 2D computational grid and a low Reynolds Number
k
–
ε
turbulence model. An improved velocity prediction was achieved by adding a gap between the doughnut internal and the pulsed column wall. The combined measurements and predictions give insight into the effect of the geometry internals on the flow hydrodynamics in the pulsed column.
•This paper presents an experimental investigation of the effect of jet velocity ratio.•Experiments for both single and two-phase flow were performed.•Both the primary jet and the lower secondary jet ...deviated from their geometric axes.•In a real furnace a large quantity of fuel will be directed close to the wall.•Such characteristics may contribute to substantial wall fouling.
The power generation industry throughout the world stands to gain significantly from process improvements and optimization which can potentially lead to cleaner production of cost effective electricity. The efficient operation of lignite-based tangentially-fired combustion systems, as commonly used in Victoria, Australia, depends on critical issues such as ignition and combustion of the fuel, which are largely controlled by burner aerodynamics. The geometry of the burner and the ratio of velocities between the primary and secondary jets play an important role in achieving stable combustion, high burnout of fuel, low production of pollutants and control of fouling. Slot-burners are vertically aligned stacks of rectangular nozzles delivering primary fuel and secondary air jets, and are commonly used in tangentially-fired boilers. To obtain a better understanding of the overall combustion process, it is important to understand the aerodynamics of jet development from these burners. This paper reports an experimental investigation into the aerodynamics of a recessed rectangular slot-burner of the type used in the Yallourn stage-2 tangentially-fired furnace. The 1:15 scale model burner consisted of a central (primary) rectangular fuel nozzle with two secondary rectangular air jets positioned above and below it. The burner jets were at an angle of 60° to the wall and were diffused and mixed in a recess before entering into the measurement vessel. A cross-flow jet was attached to the wall of the vessel to simulate the recirculation similar to tangentially-fired furnaces. Experiments for both single and two-phase flow were performed. For single-phase flow, the air flow was seeded with a fine mist of sugar particles (mean diameter 1μm) introduced into the primary, secondary and cross-flow ducts. For two-phase flow, solid glass spheres (mean diameter 66μm, density 2450kg/m3) were used as the representative of the coal particles and were introduced only at the centre of the primary duct from a bubbling fluidized bed. Experiments were conducted using a primary to cross-flow jet velocity ratio (φ) of 1.0 and secondary to primary jet velocity ratios (ϕ) of 1.0 and 3.0 as found in real furnaces. Laser Doppler Anemometry (LDA) was used to measure mean and turbulent velocity components in the near field and downstream regions of the jets. The flow pattern inside the recess was very complex and greatly influenced the flow where it entered the measurement vessel. For single-phase flow and ϕ=1.0, the jets diverged completely from the geometric axis of the burner and attached to the wall. The degree of deflection of the lower secondary jet was slightly more than the primary jet. For ϕ=3.0, after exiting from the nozzle, the primary jet diffused outwards and mixed with the higher momentum secondary jets in the recess and came out with the secondary jets. For two-phase flow and ϕ=1.0, in the mixing region between the primary and cross-flow jet, the gas-phase velocities were higher than the particle-phase. Further downstream the peak velocities of the particle-phase slightly deviated and occurred farther from the wall. For ϕ=3.0, downstream of the nozzle there was a tendency of separation for the gas-phase near the wall while the particle-phase was attached to the wall.
In a typical coal-fired power station boiler the ignition and the combustion of the fuel is largely controlled by burner aerodynamics. An experimental and numerical study of the rectangular ...slot-burners widely used on power stations in Victoria, Australia has been conducted to improve understanding of jet development within the boiler. The 1:15 scale model burner consisted of a central (primary) rectangular fuel nozzle with two (secondary) rectangular air jets positioned above and below it. The burner jets entered the measurement vessel at an angle of 60° to the wall. A cross-flow jet was attached to the wall of the vessel to simulate the recirculation prevalent in power station boilers. Experiments were conducted using a primary to cross-flow jet velocity ratio (
φ) of 1.0 and secondary to primary jet velocity ratios (
ϕ) of 1.0 and 3.0. Laser Doppler Anemometry (LDA) was used to measure mean and turbulent velocity components in the near field and downstream regions of the jets. Cross-flow significantly influenced the near field flow development from the slot-burner by deviating both primary and secondary jets from their geometric axes towards the wall. The degree of deviation was greater for
ϕ
=
1.0 since the higher velocity secondary jets increased the overall momentum of the primary jet for
ϕ
=
3.0. A numerical investigation of the rectangular slot-burner was also performed. First, the numerical results were validated against the experimental results and then visualization of the developing flow field was used to reveal the finer details of the cross-flow/burner jet interaction. Agreement between numerical and experimental jet features was good, although the numerical results predicted a primary jet that was marginally too narrow. Also the predicted downstream behaviour for
ϕ
=
3.0 deviated more significantly from experimental observation. Using the SST turbulence model, the numerical results suggested that a twin vortex was generated behind the initial region of the primary jet and this would aid in mixing of gas and fuel between primary and secondary jets.
The strength of agglomerates of nickel flash furnace concentrate and dust was determined from experimental observations of agglomerates forming under controlled conditions, combined with mathematical ...equations from the literature. It was found that the agglomerates had a tensile strength ranging from 0.01 Pa to 38.7 Pa, while inter-particle forces ranged from 2.2
×
10
−
12
N to 1.5
×
10
−
10
N. These values were compared to the expected magnitude of van der Waals, electrostatic, magnetic and capillary forces within the agglomerates, and it was found that both electrostatic and van der Waals forces are likely to contribute to the cohesion of agglomerates, although sub-micron particles and the presence of sufficiently large asperities on the surface of particles limit the magnitude of van der Waals forces. Magnetic forces are large enough to contribute to the cohesion of dust agglomerates, which is in keeping with the high magnetite content of the recycle dust. It is postulated that electrostatic forces, acting over a longer range than van der Waals forces, may be responsible for initially bringing particles together. The methodology for determining inter-particle forces can be applied to the computer modelling of flash smelting systems, as well as other gas/particle systems such as fluidized beds.
The strength of agglomerates of nickel flash furnace concentrate and dust was determined from experimental and mathematical analysis to be 0.01–38 Pa. Inter-particle forces ranged from 2.2
×
10
−
12
–1.5
×
10
−
10
N. Both electrostatic and van der Waals forces are likely to contribute to agglomerate cohesion, with electrostatic forces being responsible for initially bringing particles together.
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Fume and hygiene hoods are widely used to prevent fugitive emissions from charge ports, tap holes and many other openings in mineral processing and smelting vessels. The highly buoyant nature of the ...fume combined with often complex geometries make the design of these hoods difficult with traditional engineering tools. However, by combining the traditional engineering approach with computational fluid dynamics (CFD) techniques, a clear understanding of the shortfalls of an existing system can be obtained, and an optimised hood design can be achieved. This paper reports on a combined engineering and CFD analysis of a fume extraction system for a zinc slag fumer charge port. The engineering model revealed that the existing plant components (bag house and fan) were not capable of capturing the required amount of fume, and that the original hood design was flawed. The CFD model was then used to predict the fume capture and emission from the existing hood. CFD model predictions showed that increasing the draft flow rate by an order of magnitude would only give a marginal improvement in fume capture. Using findings of both the models enabled a new fume capture hood to be designed. CFD analysis of the new hood revealed that a significant improvement in fume capture is possible. Construction and installation of the hood has been performed and a 65% reduction in fume emission was achieved, thus significantly mitigating a long-standing emission problem.
Erosion damage caused by suspended particles in slurries leads to production loss and on-going maintenance costs. Such damage is common in flow equipment used in slurry transport, including ...processing equipment in alumina refineries.
CSIRO has been conducting research under AMIRA P931 “Multiphase Flow Erosion” projects from 2006 to 2013, under sponsorship funding support from Alcoa, BHP Billiton, Rio Tinto Alcan, Vale and Pentair Valves (Tyco Flow). CSIRO has a continuing focus on building knowledge and methods to improve prediction of the service life of flow equipment under erosion conditions, and to develop strategies to reduce erosion through altered flow design.
Interestingly, none of the case studies requested by the industry partners involved simple impingement erosion or sliding bed erosion. The emphasis has been on solving erosion problems using the principles of the underlying multiphase fluid dynamics, which called for an in-depth treatment of non-uniform flows. Consequently the current study was very different from the usual treatment of erosion (which focuses on direct impingement simply because it is easier to model and measure) and instead addressed the much more common industrial problem of localised erosion.
By using fluid dynamics modelling, experimental visualisation and quantitative measurements of erosion scars, several fluid dynamic mechanisms have previously been identified as causing severe erosion attacks. These included erosion by vortices, by flashing and by various non-uniform flows. Observations of accelerated wear have shown that vortex erosion is present in many flow geometries critically important in sponsors' plants, e.g. pipe work around a valve, protrusions in a pipe and many conventional engineering designs. This paper focuses on vortex erosion in a variety of flow situations and examines the fluid dynamics and consequent erosion.
•Flow disturbances in slurry flow result in damaging localised erosion.•Vortex erosion in slurry flows is significantly more damaging than impact.•Changes in fluid flow geometry offer a means of reducing vortex erosion.
The model results (Table III) indicate that the system has many routes for ambient air to enter it. and by eliminating all of the in-leakage into the flues (Run 2). a nearly equivalent increase in ...the infiltration occurred through the hoods. By eliminating in-leakage and also using hood gales and dampers (Run 10), it was possible to increase the hood draft and also decrease total flow by 9.7%, leading to an increase in SO^sub 2^ concentration from 1.23% to 1.38%.
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