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This study investigates the impact of buoyancy on the mixing and flame structure of hydrogen jet diffusion flames. A validated Computational Fluid Dynamics (CFD) model for hydrogen diffusion flames is developed, employing the k − ω turbulence model and a steady flamelet combustion model. By accounting for the buoyancy term, the model accurately predicts the stoichiometric hydrogen flame length within a mere 0.2% deviation from the experimental value. In contrast, excluding the buoyancy term leads to a prediction divergence of around 5%. Deeper analysis of the mixture fraction field indicates that buoyancy enhances mixing in the flame's far-field region, facilitating a more rapid dilution of the fuel stream within the air. This, in turn, results in a shorter flame. The scope of the modelling is expanded to encompass buoyancy effects on hydrogen flames with jet Reynolds numbers (R e J ) up to 15,000. While the buoyancy's influence on flame control weakens as R e J increases, a noticeable ∼ 4% variation in stoichiometric flame length persists between scenarios with and without buoyancy. • Accounting for buoyancy enhances H 2 flame prediction accuracy in CFD simulations. • Buoyancy boosts fuel-air mixing; its impact on reaction kinetics is negligible. • Buoyancy effect weakens with increasing jet velocity, but remains noticeable. [ABSTRACT FROM AUTHOR]

Abstract: This study reports on numerical predictions of velocity and pressure fields, and dust particles trajectories in steady and unsteady flows around a full-scale paraboloidal solar dish. Calculations are performed for three wind speeds of 4.16, 9.72, and 15.2 m s−1, and dish pitch angles from 0° to 180°. The flow field structure, lift and drag coefficients are calculated for each flow configuration. Using the predicted mean flow velocity field, analytical expressions for the aerodynamic coefficients, as a function of the pitch angle, are developed. The unsteady-state flow is characterised by formation of stable vortices behind the dish for most flow configurations, except at 60° and 150° pitch angles. At these angles vortex-shedding occurred with a strong flow oscillation extending downstream the dish. The calculations of dust particles trajectories provide a qualitative assessment of the deposition rate, dish orientation, and surface locations where dust accumulation is most likely to occur. The study also presents an initial assessment of the effectiveness of various windbreaks installed upstream of the dish in reducing aerodynamics drag. [Copyright &y& Elsevier]

Experimental testing and validated CFD models have been used to evaluate the performance of the FC4GT flameless gas turbine (GT) combustor operating at a global equivalence ratio of 0.44. The methane-fuelled combustor was tested at atmospheric pressure, modelled at elevated pressures up to 25 bar, and optimised for a combustor pressure of 15 bar. The combustor was analysed for firing rates between 15 kW and 16 MW, which correspond to heat density range between 0.15 MW/m3.bar and 150 MW/m3.bar, respectively. The performance of the combustor was also evaluated with pure hydrogen. Overall, the flow fields while using both fuels, are found to be similar; exhibiting highly uniform spatial (temperature and oxygen) distributions, and low exhaust NO x emissions. Volumetric histograms of temperature and oxygen in the combustor are identified as a powerful analysis tool for quantifying the level of uniformity of the scalar mixing and combustion field, NO x emission, and for determining the combustion regime. The momentum flux of the primary air jet has been identified as a key parameter in controlling NO x emission. Across the power generation mode for GT operation with a heat density of 5–150 MW/m3.bar, the predicted NO x emission (15% O 2 dry) for methane was 34–6 ppm v , respectively, and for hydrogen 353–33 ppm v , respectively. At 50 MW/m3.bar, the predicted NO x emission for methane was 17 ppm v , and 146 ppm v for pure hydrogen. This is a significant outcome for a non-premixed combustor considering that the NO x emission of the GE6FA GT engine using partially premixed combustion at 50 MW/m3.bar, is 15 ppm v for methane, and 200 ppm v for 85% hydrogen. Overall, the low NO x emission, for methane and hydrogen, combined with the highly uniform spatial temperature and oxygen distributions, and supported by experimental visualisation provide irrefutable proof that a flameless combustion regime has been achieved. It also demonstrates the plausibility of a non-premixed flameless combustor achieving comparable NO x emission to premixed flames. [ABSTRACT FROM AUTHOR]

Fertilizers have been given significant attention due to their critical need for agriculture yield to meet the demand for food growth arising from population growth. The demand for potassium fertilizer (metric tons of K 2 O) has increased by 12% between 2015 and 2020. Therefore, the concern about the limited availability of soluble potassium resources in the southern hemisphere has become a key research focus for identifying alternative resources and technologies. This study presents a review of the fundamental knowledge of alternative technologies, such as acid leaching, hydrothermal and molten salt technology, as well as different alternative K-bearing silicate resources (ultrapotassic syenite, nepheline syenite, glauconitic sandstone and mica). Studies on fluxing agents proposed for the extraction of K+ based on different methods were analysed and compared. This paper offers a detailed overview of experimental kinetic analysis, kinetic and mechanism reactions, aims to improve the extraction technology and address relevant industry challenges. This review also reports on thermodynamic analysis of the mineral-salt/acid/alkaline systems, providing insights into the basis of industrial applications. Finally, the review provides opportunities and challenges of each technique and has shown that further techno-economic and process analysis are required to better identify the viability of each technique for large-scale industrial demonstration. [ABSTRACT FROM AUTHOR]

[Display omitted] The blood-brain barrier (BBB) is a strong barrier against the entrance of drugs, which has made brain cancer treatment a major challenge. We have previously shown that targeting transferrin receptors using aptamers increased brain drug delivery. To get a better understanding of this phenomenon, in the present article, a mathematical model based on the finite element method was developed accounting for the fluid flow and mass transport of the aptamer molecule inside an 8 µm capillary vessel across a 14 µm blood-brain barrier domain. The fluid flow and mass transport equations were coupled to calculate the blood velocity and aptamer concentration profiles across the BBB. It was identified that the thickness of the astrocyte and endothelial cell layers are key parameters affecting the concentration of the aptamer delivered to the last neuron dendrites in the BBB. The predicted efficacy of the drug delivery (C apt /C in) of 10.9% to 13.8% was calculated at a porosity of 0.5 to 0.9, respectively, at a blood velocity of 0.38 mm/s, which was independent of the inlet concentration of the aptamer. This low efficacy was attributed to the mass transfer resistance across endothelial cells, astrocyte and pericyte layers, which decreased the concentration by 6.7%. It was also identified that the main mechanism of drug delivery is switched from convective mass transport in the capillary layer (with Peclet number > 50) to mixed convection mass transport (1 < Peclet number < 5) in the porous layers and to diffusion only once aptamer reached the brain parenchyma (Peclet number < 1). [ABSTRACT FROM AUTHOR]

Face masks and respirators are used to filter inhaled air, which may contain airborne droplets and high particulate matter (PM) concentrations. The respirators act as a barrier to the inhaled and exhaled air, which may change the nasal airflow characteristics and air-conditioning function of the nose. This study aims to investigate the nasal airflow dynamics during respiration with and without an N95 respirator driven by airflow through the nasal cavity to assess the effect of the respirator on breathing conditions during respiration. To achieve the objective of this study, transient computational fluid dynamics simulations have been utilized. The nasal geometry was reconstructed from high-resolution Computed Tomography scans of a healthy 25-year-old female subject. The species transport method was used to analyze the airflow, temperature, carbon dioxide (CO2), moisture content (H2O), and temperature distribution within the nasal cavity with and without an N95 respirator during eight consecutive respiration cycles with a tidal volume of 500 ml. The results demonstrated that a respirator caused excessive CO2 inhalation by approximately 7 × greater per breath compared with normal breathing. Furthermore, heat and mass transfer in the nasal cavity was reduced, which influences the perception of nasal patency. It is suggested that wearers of high-efficiency masks that have minimal porosity and low air exchange for CO2 regulation should consider the amount of time they wear the mask. [ABSTRACT FROM AUTHOR]

Despite its long history of technological development, much charcoal production still relies on polluting and inefficient technologies utilizing traditional kiln designs. In addition to the need for improved charcoal production systems, the growing interest globally in pyrolysis of biomass to generate biochar as a soil fertility improver and for climate change mitigation may drive an increasing demand for such technologies. Accordingly, there is a clear need in developing countries for access to safe, affordable, and efficient open-source designs and technology that can be fabricated locally. The design described here includes computational fluid dynamics modeling which demonstrated that the design exhibits a stable flow and combustion pattern. A hazard and operability (HAZOP) study, mass and energy modeling, and costing of all components and fabrication were also conducted for a prototype kiln that will accept up to 250 kg biomass h-1. Fabrication and installation costs were estimated using actual commercial quotations based on detailed engineering drawings and design, and were found to be $580 000 for a 250 kg h-1 unit. We therefore find that this pyrolysis system promises to be economical on a small scale. It can utilize waste lignocellulosic materials for feedstock, thus alleviating demand pressure on woodlands to provide feedstocks. It was, therefore, concluded that the pyrolysis unit described here promises to provide an affordable and efficient open-source design that can be fabricated locally in developing countries without licensing restrictions or royalties. © 2017 The Authors Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd [ABSTRACT FROM AUTHOR]

The capture and activation of individual T cells on functionalised surfaces enables real-time analyses of the magnitude and rhythm of intracellular calcium release. Application of Haarlet transformations generate a calcium flux 'threshold', with the frequency of the 'threshold crossings' correlating with the strength of the original T cell stimulus. These findings represent a new method to evaluate graduations in T cell activation in real time, and at a single-cell level. [ABSTRACT FROM AUTHOR]

The cover image, by Dominic Woolf et al., is based on the In the Field An open-source biomass pyrolysis reactor, DOI: . [ABSTRACT FROM AUTHOR]