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A general calculation for the distribution of non-uniform demagnetization fields in paramagnetic bulk solids is described and the fields for various sample geometries are calculated. Cones, ellipsoids, paraboloids, and hyperboloids with similar sample aspect ratios are considered. Significant differences in their demagnetization fields are observed. The calculation shows that the demagnetization field magnitudes decrease along the axis of symmetry (along z) where an externally applied magnetic field is aligned, and increase in the vicinity of the lateral surfaces with the largest field values found in the cone and the narrowest field distributions found in the hyperboloid. An application is made to the theoretical modeling of the 1H-NMR spectra of a single crystal of field-induced superconductor λ-(BETS)2 FeCl4 with a rectangular sample geometry, providing a good fit to the measured NMR spectra. [ABSTRACT FROM AUTHOR]

The photo-oxidation of water on the monoclinic P21/nWO3 (200, 020, and 002) surfaces is investigated using density functional theory calculations, employing the PW91-generalized gradient approximation, and the method developed by No\rskov et al. [J. Phys. Chem. B 108, 17886 (2004)] based on the free energy differences between the reaction intermediates. We first relax the bulk material unit cell and then investigate the relative stability of different surface terminations of WO3 and analyze the overpotential needed for the photoelectrolysis of water. We found that the rate limiting step is the transfer of a proton from the surface adsorbed OH to the electrolyte, and that the computed overpotential for O2 evolution (1.04 V) is available upon illumination of the surface with visible light. [ABSTRACT FROM AUTHOR]

The photo-oxidation of water on the monoclinic P21/nWO3 (200, 020, and 002) surfaces is investigated using density functional theory calculations, employing the PW91-generalized gradient approximation, and the method developed by No\rskov et al. [J. Phys. Chem. B 108, 17886 (2004)] based on the free energy differences between the reaction intermediates. We first relax the bulk material unit cell and then investigate the relative stability of different surface terminations of WO3 and analyze the overpotential needed for the photoelectrolysis of water. We found that the rate limiting step is the transfer of a proton from the surface adsorbed OH to the electrolyte, and that the computed overpotential for O2 evolution (1.04 V) is available upon illumination of the surface with visible light. [ABSTRACT FROM AUTHOR]

Using the random-phase approximation and self-consistent field calculations, we have investigated the effects of finite interaction range and compressibility on the order-disorder transition (ODT) and the lamellar structure of symmetric diblock copolymers. While the compressibility does not affect the ODT, both the values of χN and bulk lamellar period at the ODT increase with increasing interaction range. On the other hand, both the free-energy density and bulk period of the lamellae increase with either increasing interaction range or decreasing compressibility. Even with a finite compressibility, the mean-field ODT is still a second-order phase transition. The scaling exponent of bulk lamellar period with χN, however, decreases with increasing compressibility. Our mean-field analysis provides a well understood reference for the study of fluctuation effects in diblock copolymers with finite interaction range and compressibility. [ABSTRACT FROM AUTHOR]

Highlights • Hydrodynamics in upward and downward liquid-solid CFB are compared by CFD approach. • A good agreement is achieved between the numerical and experimental results. • Similarities and differences are presented between the upward and downward CFB. • The previous Sang and Zhu model is proven to be useful in predicting solids holdup. Abstract The flow behaviors of the particles in the upward and downward liquid-solid circulating fluidized beds were simulated by Eulerian-Eulerian approach incorporating the kinetic theory of granular flow. The Syamlal-O'Brien drag model was used to account for the interphase interaction between the liquid and solids phases. The numerical results agreed well with the experimental data obtained by other group members, successfully validating the numerical approach. The hydrodynamic characteristics of the particles with different densities and sizes in the upward and downward circulating fluidized beds were compared in detail under different liquid velocities and solids flow rates. The results indicated that there were many hydrodynamic similarities in the upward and downward circulating fluidized beds. However, due to the deviation of the standard drag curve, the drag force on the lighter particles in the downward liquid-solid circulating fluidized bed became different, leading to random and irregular particle flow behaviors. The predicted average solids holdups matched well with the results by an empirical model proposed by Sang and Zhu and the matching degree between the numerical results and the model was larger than 85%, further proving that the Sang and Zhu model is widely applicable. [ABSTRACT FROM AUTHOR]

Detailed understanding the particle mixing and segregation dynamic is essential in successfully designing and reasonably operating multicomponent fluidized bed. In this work, a novel fluorescent tracer technique combining image processing method has been used to investigate the mixing and segregation behavior in a binary fluidized bed with wide size distributions. The particle number percentage in each layer for different gas velocities is obtained by an image processing method. Fluidization, mixing and segregation behavior has been discussed in terms of bed pressure drop, gas velocity and mixing index. Different types of binary particle systems, including the jetsam and the flotsam-rich system, are analyzed and compared. The mixing indexes at different minimum fluidization velocities are also analyzed and compared with other work. The results show that the theoretical minimum fluidization velocity calculated from the bed pressure drop cannot represent the whole fluidization for a wide size distribution binary particle system. The effect of a wide size distribution is an inflection point in the mixing index curve. There is also a dead region in the bottom of the bed that consists of particles with large size and a low degree of sphericity. The particles in the dead region are extraordinarily difficult to fluidize and should be considered in the design of fluidized beds in industrial applications. [ABSTRACT FROM AUTHOR]

We present an improved minimal variance (MV) method for using a radial peculiar velocity sample to estimate the average of the three-dimensional velocity field over a spherical volume, which leads to an easily interpretable bulk flow measurement. The only assumption required for this interpretation is that the velocity field is irrotational. The resulting bulk flow estimate is particularly insensitive to smaller scale flows. We also introduce a new constraint into the MV method that ensures that bulk flow estimates are independent of the value of the Hubble constant H 0; this is important given the tension between the locally measured H 0 and that obtained from the cosmic background radiation observations. We apply our method to the Cosmicflows-3 catalogue and find that, while the bulk flows for shallower spheres are consistent with the standard cosmological model, there is some tension between the bulk flow in a spherical volume with radius 150  h −1 Mpc and its expectations; we find only a |${\sim } 2{{\, \rm per\, cent}}$| chance of obtaining a bulk flow as large or larger in the standard cosmological model with Planck parameters. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The flow of particulate materials is critical during processes such as mixing, compression and packing. Non-cohesive arching, a feature characteristic of coarse and free-flowing particles, has been studied extensively for silos and hoppers. However, the arching of powders during die fill has received much less attention. In this study, die fill performance of coarse and free-flowing nonpareils was evaluated using a specially designed die filling device in order to investigate the impact of non-cohesive arching during die fill under gravity flow. Through evaluating die fill performance, the arching phenomenon during dynamic conditions of die fill could be captured. Nonpareils with large particle size increased the likelihood of arching and caused poorer die fill performance for narrow orifices. In contrast, die fill in large orifices was generally better with larger particles due to reduced inter-particulate friction. Both particle size and size distribution influenced non-cohesive arching during die fill. Forced feeding did not appear to affect die fill performance and non-cohesive arching. A critical particle size range beyond which die fill performance would decrease, particularly for the narrow orifices, was identified. Findings from this study provided a better insight into non-cohesive arching during die fill. [ABSTRACT FROM AUTHOR]

The unsteady flow field and pressure fluctuations in double-suction centrifugal pumps are greatly affected by the wall roughness of internal surfaces. To determine the wall roughness effect, numerical and experimental investigations were carried out. Three impeller schemes for different wall roughness were solved using detached eddy simulation, and the performance and pressure fluctuations resolved by detached eddy simulation were compared with the experimental data. The results show that the effects of wall roughness on the static performance of a pump are remarkable. The head and efficiency of the tested double-suction centrifugal pump are raised by 2.53% and 6.60% respectively as the wall roughness is reduced by means of sand blasting and coating treatments. The detached eddy simulation method has been proven to be accurate for the prediction of the head and efficiency of the double-suction centrifugal pump with roughness effects. The influence of the roughness on pressure fluctuation is greatly dependent on the location relative to the volute tongue region. For locations close to the volute tongue, the peak-to-peak value of the pressure fluctuations of a wall roughness of Ra = 0.10 mm may be 23.27% larger than the case where Ra = 0.02 mm at design flow rate. [ABSTRACT FROM AUTHOR]

The article discusses the methods for measuring bulk solids flow properties in order to design bins, silos, and hoppers for reliable flow. Topics include methods for measuring internal friction, cohesive strength, and compressibility. It offers information on the value of wall friction angle and presents graphs representing permeability.

The Jenike flowability classification is designed to indicate the handleability of bulk solids in material handling processes. However, for moist, cohesive bulk solids, it may fail to represent the true flowability/handleability at high consolidation stresses. The study presented in this paper introduces a modified flowability classification model aiming to improve the flowability/handleability prediction across a wide range of consolidation pressures. The evolution of the flow function of bulk materials under increasing moistures is initially discussed, based on which the Jenike flowability classification is reviewed. The modified flowability classification is then derived by considering the flow/no flow condition for mass flow hopper designs under both low and high consolidation stress states. The influence of the bulk material type and general operational conditions are also taken in account in deriving the modified classification method. A suite of bulk solids with a wide range of material properties are selected in an experimental program to validate the modified flowability classification. Results suggested the modified flowability classification is able to more accurately indicate the overall flowability/handleability of the bulk solids independent of the applied major consolidation stress. [ABSTRACT FROM AUTHOR]

This present study analyses the effects of the concentration of solids in the over-elevation phenomenon in a canal with a 180° curvature and a constant trapezoidal transversal section, with a firm bed, the fluid has a non-colloidal, mono-disperse distribution of relatively spherical particles of 1mm in size, thus making the rheology of the flow describable by the Einstein-Roscoe equation (1). Two stages are proposed for the development of the research; the first corresponds to physical experimentation, achieved using an artificial canal, in which 420 tests were carried out using different concentration of solids and two slopes, in order to determine the behaviour of the bi-phased flow. All of this is carried out by using experimental results and results obtained from numerical models. The data collected from the experimental process is compared to the results obtained from the theoretical models that are reported in literature. An over-elevation equation was formulated from the analysis, which can be used for the bi-phased conditions described in this article. During the second phase, numerical modelling using the TITAN2F software was carried out, where laboratory conditions are replicated. Data found from numerical modelling is compared with experimental results, with the intention of validating the numerical model that TITAN2F uses. From what is mentioned above, it was deduced that TITAN2F effectively reproduces the hydraulic phenomenon. However, it is also observed that the program has a low susceptibility to changes in the concentration of solids, due to the scale being used. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) is a technology of CO 2 capture that can drastically reduce its cost. The solids circulation inside a 100-kW chemical looping combustor was investigated using a novel oxygen carrier called Sinaus by adding fuel batches to the fuel reactor. The decline and subsequent rise of oxygen concentration in the air reactor after each addition was used to determine the residence time of solids in the fuel reactor and adjacent vessels. The obtained residence time, in combination with the solids inventory, determined the solids circulation for a particular batch experiment. After performing a number of such experiments, the above circulation was correlated with other experimental data, revealing a good correlation between the solids flow at the top of the air reactor riser and the actual circulation obtained using batch tests. The relationship between global circulation, m ̇ , and the mass flow in the air reactor riser, m ̇ riser , was found to be linear within the investigated interval, being described as m ̇ = 6.6 + 0.057 m ̇ riser . Although this correlation was valid only for the investigated reactor system, the approach used to obtain the solids circulation could be used to derive a similar correlation for any dual fluidized bed system. [ABSTRACT FROM AUTHOR]

The microwave plasma torch (MPT) is an attractive plasma source in both industry and scientific research because of its advantages in electrodeless operation ability, high energy efficiency, and flexibility under different operational conditions. However, relatively few numerical studies have been carried out for the MPT fed by a rectangular waveguide in two or even three dimensions. Therefore, this paper presents a 2-D, axisymmetric, and stationary fluid models to characterize the MPT, with an emphasis on the mechanism of the surface wave formation and the sustentation of the plasma column. Nine partial differential equations are included in this research, coupling microwave radiation, heat transfer, plasma bulk flow, and transport of different species with each other. The obtained results reveal how the traveling surface wave occurs and elucidate the consequent influence of the surface wave formation. Furthermore, this paper demonstrates the extension of the plasma column length and the propagation of the surface wave with an increase in the total plasma-absorbed microwave power. The dependence of the plasma column length on the plasma-absorbed microwave power is found to be motivated by the surface wave propagation. The limitations of the model and the difficulties in its numerical implementation are also discussed in the paper. [ABSTRACT FROM PUBLISHER]

A bubbling fluidized bed (BFB) with a continuous feed/discharge of solids was used as a gasifier in a high-density triple-bed circulating fluidized bed (TBCFB). To carry the heat from the combustor to the pyrolyzer/gasifier effectively, a high-density and high solids-mass flux circulating system is necessary. In this study, the gas-solid flow behavior of a BFB with high solids continuous feeding/discharging mass flux was simulated by an Eulerian–Eulerian model incorporating the Lagrangian (discrete phase model) properties of particles as a tracer to analyze particle motion and determine the optimal feeding tube location and diameter. It was observed that a U-shaped track of particles from the inlet to the outlet and double vortices resulted in particle back-mixing and extended particle residence time. According to the results, some feeding-tube design principles were proposed to achieve smooth solids flow and improve the particle residence time in the BFB in solids mass circulating fluxes ranging from 800 to 1200 kg/m 2 s. [ABSTRACT FROM AUTHOR]

Three-dimensional full-loop simulation of a high-density circulating fluidized bed (HDCFB) is conducted using the multiphase particle-in-cell (MP-PIC) method. The computational results are in good agreement with the experimental data of pressure distribution and solids circulation rate under different aeration conditions of the standpipe. The main feature of gas-solid flow in the riser is qualitatively predicted, with coexistence of the developed flow in the upper region and the acceleration flow in the lower region. The flow regime in the standpipe is mainly concurrent downward gas-solid flow in the close packing region. Due to the influence of the aeration gas, the pressure gradient presents a wave variation along the height of standpipe. The predicted solids residence time distribution in the standpipe exhibits a feature of early peak with an extended tail, indicating that the solids flow is not uniform in the standpipe. [ABSTRACT FROM AUTHOR]

This work assesses the solids circulation rate in a circulating fluidized bed cold model based on measuring the particles mean residence time ( τ ). The tracking method detects fluid-dynamically similar ferromagnetic tracer particles, and is based on inductance changes of a coil due to changes in the concentration of ferromagnetic particles in its core. A section of the model was selected to perform the tracer measurement, such that the variations in the solids volumetric fraction and the solids velocity were negligible, and a correlation between the circulation rate and the mean residence time of solids could be established. The circulation rate was calculated in this manner for a range of operation conditions, variations of riser fluidization velocity and total inventory were performed. The results were validated measuring the circulation rate by the accumulation method as well, the results show a satisfactory correlation between the tracer and the accumulation methods. The magnetic tracer method appears thus to be suitable for the measurement of solids circulation rates in low temperature applications. This method offers as advantages the possibility for on-line measurement, good sensitivity, non-intrusiveness, cost efficiency, and does not require a calibration. [ABSTRACT FROM AUTHOR]

Fluidization of particles with a high moisture content and wide size distribution is difficult. In this study, pulsation-assisted flow (PAF) was used to enhance the fluidization of wet particles with a wide size distribution. The combination of pulsed and steady flow increased the particle-mixing rate and broke the liquid bridge between solid particles, which prevented particle agglomeration. PAF enhanced the fluidization performance by increasing the separation rate of large particles, thus narrowing the size distribution in the fluidized bed. The effect of PAF on the fluidization performance was also investigated using a newly developed fluidization model, which was verified by comparison with experimental results. The model was used to investigate the relationship between bubble size and pulsed flow frequency, as well as the effect of pulsed flow frequency on particle agglomeration. The model could also predict the optimal pulsed flow frequency for fluidization of wet particles. [ABSTRACT FROM AUTHOR]

Changes of bulk flow properties of two different types of titanium dioxide powders were measured at room temperature and 500 °C using the High Temperature Annular Shear Cell. A significant increase of the macroscopic bulk flow properties was observed with increasing temperature, in particular with regard to the unconfined yield strength. A theoretical modelling procedure was proposed with the aim to relate the measured properties to the microscopic interactions between particles. The results indicated that the model might provide a good match with the experimental data if proper values for the model's parameters are taken into account. [ABSTRACT FROM AUTHOR]

In chemical and energy industries, fluidization concerning rod-like particles is often encountered, but little effort has been made in this respect. Understanding fluidization of rod-like particles is crucial for the guidance of relevant industrial process. To investigate the fluidization of the rod-like particles with different aspect ratios, CFD-DEM coupling algorithm is employed in this article to simulate a bubbling fluidized bed, in which the rod-like particles are modeled by super-ellipsoids. The simulations results show that, in the case of same particle volume, the rod-like particles with smaller aspect ratio obtain larger force from the gas and the particles can absorb more energy from fluid flow, and the fluidization phenomenon, like slugging and bubbles, is easier to form. The local voidage fraction and particle's projected face area perpendicular to fluid flow direction are directly related to particle orientations, which have great influence on drag force and fluidization. Due to the significance of particle orientation, a further investigation is made for the factors that influence the distribution of particle orientation. The results show that particle orientation is greatly affected by fluidization time, fluidization velocity, and the structure of the fluidized bed. [ABSTRACT FROM AUTHOR]

Non-cohesive materials such as sand, dry snow or cereals are encountered in various common circumstances, from everyday situations to industry. The process of digging into these materials remains a challenge to most animals and machines. Within the animal kingdom, different strategies are employed to overcome this issue, including excavation methods used by ants, the two-anchor strategy employed by soft burrowers such as razor-clams, and undulatory motions exhibited by sandfish lizards. Despite the development of technology to mimic these techniques in diggers and robots, the limitations of animals and machines may differ, and mimicry of natural processes is not necessarily the most efficient technological strategy. This study presents evidence that the resisting force for the penetration of an intruder into a dry granular media can be reduced by one order of magnitude with small amplitude (A ≃ 10 μm) and low frequency (f = 50 − 200 Hz) mechanical vibrations. This observed result is attributed to the local fluidization of the granular bed which induces the rupture of force chains. The drop in resistive force on entering dry granular materials may be relevant in technological development in order to increase the efficiency of diggers and robots. [ABSTRACT FROM AUTHOR]