Hydrodynamic characteristics of gas–solid fluidization at high temperature

Effect of temperature on the hydrodynamics of bubbling gas–solid fluidized beds was investigated in this work. Experiments were carried out at different temperatures ranged of 25–600°C and different superficial gas velocities in the range of 0.17–0.78 m/s with sand particles. The time‐position trajectory of particles was obtained by the radioactive particle tracking technique at elevated temperature. These data were used for determination of some hydrodynamic parameters (mean velocity of upward and downward‐moving particles, jump frequency, cycle frequency, and axial/radial diffusivities) which are representative to solids mixing through the bed. It was shown that solids mixing and diffusivity of particles increases by increasing temperature up to around 300°C. However, these parameters decrease by further increasing the temperature to higher than 300°C. This could be attributed to the properties of bubble and emulsion phases. Results of this study indicated that the bubbles grow up to a maximum diameter by increasing the temperature up to 300°C, after which the bubbles become smaller. The results showed that due to the wall effect, there is no significant change in the mean velocity of downward‐moving clusters. In order to explain these trends, surface tension of emulsion between the rising bubble and the emulsion phase was introduced and evaluated in the bubbling fluidized bed. The results showed that surface tension between bubble and emulsion is increased by increasing temperature up to 300°C, however, after that it acts in oppositely.     

Comparison of the Calculated Drought Return Periods Using Tri-variate and Bivariate Copula Functions Under Climate Change Condition

Water Resources Management - Concerning the various effects of climate change on intensifying extreme weather phenomena all around the world, studying its possible consequences in the following...     

The Synthesis and Characterization of Hard-Soft Mn52Al45.7C2.3-α-Fe Nanocomposite Magnets

We report on the magnetic exchange coupling behavior in hard-soft Mn₅₂Al_45.7C_2.3-α-Fe nanocomposite magnets synthesized by high-energy ball milling at room temperature followed by post-annealing treatment at temperatures 300 to 600 °C. The analysis of hysteresis loops showed effective exchange coupling Mn₅₂Al_45.7C_2.3-α-Fe nanocomposite particles with smooth demagnetizing curves when annealed at 400 °C. But higher annealing temperatures pose kink in the hysteresis loop highlighting a weak exchange coupling with more magnetostatic interaction between hard and soft components. This trend was confirmed by the results on (BH)_max, which had the highest value for nanocomposite particles annealed at 400 °C. More detailed information on magnetic exchange coupling in nanocomposite particles was obtained by derivative magnetic curves and Henkel plots. Hard-soft Mn₅₂Al_45.7C_2.3-α-Fe magnets showed the sharpest high-field maximum in derivate magnetic curves when annealed at 400 °C as a signature of effective exchange coupling between Mn₅₂Al_45.7C_2.3 and α-Fe grains. In addition, Henkel plots display the dominance of positive peak for nanocomposite particles annealed at 300 and 400 °C, indicative of magnetic exchange-coupling. But the negative-peak dominated curves of those annealed at higher temperatures as well as single-phase Mn₅₂Al_45.7C_2.3 imply a significant magnetostatic interaction in the components owing to non-magnetic phases formed at elevated temperatures. Also, quantitative information obtained from recoil curve measurements assigned a higher degree of exchange coupling to nanocomposite magnets when annealed at 400 °C.

     

Examination the Grain Size Dependence of Exchange Coupling in Oxide-Based SrFe12O19/Ni0.7Zn0.3Fe2O4 Nanocomposites

Magnetic hard/soft SrFe₁₂O₁₉/Ni_0.7Zn_0.3Fe₂O₄ nanocomposites were fabricated by a two-step chemical procedure. Strontium hexaferrite NPs were synthesized via sol–gel self-propagation and then dispersed in nickel–zinc ferrite sol to prepare oxide nanocomposites by the glyoxilate precursor method. The initial product was annealed at different temperatures to study the effect of grain size on the magnetic properties of composite hard/soft ferrites. The magnetic nanoparticles (MNPs) were characterized by XRD, FTIR, TEM, and VSM techniques. Magnetic measurements indicated concave hysteresis loops for these two-phase nanocomposites due to non-complete exchange coupling at the interfaces of hard and soft ferrites. This phenomenon could be attributed to the overcritical size, 46 nm, of the hard phase, based on the critical limit of 22 nm predicted by theoretical calculation. At high annealing temperature with increasing the size of the soft phase as well as the hard phase, the dipolar interaction became dominant and the magnetic behavior of hard/soft nanocomposites approached two-phase uncoupled magnets.     

Modeling of mass transfer and thermal cracking during the coking of Athabasca residues

The kinetics of thermal cracking of films of vacuum residue from Athabasca bitumen in the temperature range of was modelled with liquid-phase mass transfer, reaction-dependent fluid properties, and coke formation by reaction of cracked products in the liquid phase. Previous investigations on the thermal cracking of vacuum residue in thin films showed that at low film thickness the coke yield was insensitive to the temperature and heating rate for thin films of bitumen. The coke yield increased with the thickness of the initial film, in the range from 20 to . At the same time, the viscosity of the reacting liquid increased rapidly with time, which would slow down the diffusion of products inside the film. This coupling of transport and reaction would enhance the formation of coke by increasing the rate of recombination reactions. The concept of intrinsic coke is used in a new kinetic model to account for the minimum observed coke formation in thin films. With increasing film thickness, the increasing yield of extrinsic coke is modelled through the change in fluid properties as a function of extent of reaction, which reduces the rate of diffusion in the reacting liquid phase. The model was able to properly account for the insensitivity of coke yield in thin films to reaction temperature and the dependence of coke yield on the thickness of the liquid film.     

Numerical analysis and computer simulation of magnetostatic wavepropagation in a YIG-loaded waveguide

Magnetostatic wave (MSW) propagation in a finite-width ferrite slab placed inside and along a rectangular waveguide is investigated theoretically and numerically. Using the integral equation method, the general solution to the problem of wave propagation is derived. Thin-slab approximation makes the derived solution more tractable and provided the dispersion relations in terms of an infinite determinant. From the results presented, it can be concluded that, in order to obtain a high value of group time delay over a large bandwidth, thin, narrow slabs placed in the center of the guide must be used. On the other hand, to maximize the device bandwidth, thin slabs placed at the top or bottom of the guide are most appropriate     

A unified lumped approach in kinetic modeling of biomass pyrolysis

Thermogravimetry analysis and gas chromatography techniques are used at different heating rates (from 5 to 50 K/min) to map all the products and to develop suitable kinetic models of biomass pyrolysis. A three-independent-parallel-reactions model is used to model kinetic of total devolatilization. This part accounts for the total char yield and devolatilization time. The evolutions of condensable vapors (tar and H₂O) and non-condensable gases (H₂, CH₄, CO and CO₂) are also studied using gas chromatography technique. It is shown that the final total yield of gases increases by increasing the heating rate, whereas those of tar decrease by increasing heating rate. A kinetic model was then proposed and the parameters for that were calculated, which can predict the change of the gases yields at different heating rates. The performance of the kinetic models was evaluated for other experimental works available in the literature or by exposing the biomass to different heating program.     

Investigation of Magnetic Interactions in Core/Shell Structured SrFe12O19/NiZnFe2O4 Nanocomposite

SrFe₁₂O₁₉ magnetic nanoparticles (MNPs) were synthesized by a sol-gel self-propagating method and subsequent heat treatment. The SrFe₁₂O₁₉/NiZnFe₂O₄ core/shell MNPs were obtained by coating the SrFe₁₂O₁₉ MNPs by glyoxilate precursor method using metallic nitrates and ethylene glycol. The core/shell was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM) techniques. Comparison of the observations with theoretical criteria indicated that the demagnetization behavior of composite NPs is in exchange spring mode. This phenomenon is attributed to the overcritical size, 46?nm, of the hard phase, which leads to partial exchange coupling between hard- and soft-magnetic phases.     

Video-Based Automatic Incident Detection for Smart Roads: The Outdoor Environmental Challenges Regarding False Alarms

Video-based automatic incident detection (AID) systems are increasingly being used in intelligent transportation systems (ITS). Video-based AID is a promising method of incident detection. However, the accuracy of video-based AID is heavily affected by environmental factors such as shadows, snow, rain, and glare. This paper presents a review of the different work done in the literature to detect outdoor environmental factors, namely, static shadows, snow, rain, and glare. Once these environmental conditions are detected, they can be compensated for, and hence, the accuracy of alarms detected by video-based AID systems will be enhanced. Based on the presented review, this paper will highlight potential research directions to address gaps that currently exist in detecting outdoor environmental conditions. This will lead to an overall enhancement in the reliability of video-based AID systems and, hence, pave the road for more usage of these systems in the future. Last, this paper suggests new contributions in the form of new suggested algorithmic ideas to detect environmental factors that affect AID systems accuracy.     

Effects of starch addition on the characteristics of CoAl2O4 nano pigments

Nanocrystalline cobalt aluminate spinel, CoAl₂O₄, was prepared via a microwave‐assisted solution combustion process applying various mixtures of urea, glycine, and starch as a novel mixed fuel. The effects of starch addition (0, 10, 20, and 30 wt%) on the physical characteristics (e.g. crystallite size and colour) of the blue nano pigments were also investigated. The resultant powders were characterised by means of X‐ray diffraction, scanning electron microscopy, electron dispersive X‐ray analysis, and CIE L*a*b* colour measurements. The presence of a CoAl₂O₄ spinel lattice after calcination of precursors at 600 °C was confirmed by X‐ray diffraction patterns, and the crystallite sizes were ca. 10–39 nm. Colorimetric data pointed to the formation of bright‐blue pigments at low levels of starch addition. Scanning electron microscope images showed that starch enrichment reduced the agglomeration and size of synthesised nanoparticles.