Powder Technology最新文献

Mini-fluidized beds (MFBs) can significantly enhance the mass transfer, heat transfer and mixing process. In this study, planar laser induced fluorescence method (PLIF) was used to evaluate the mixing performance in liquid-solid mini-fluidized beds. In contrast to the particle-free tubes, the relative mixing index, mixing length, mixing time, specific power consumption, mixing effectiveness and energy efficiency of mini-fluidized beds with inner diameters of 1–3 mm were analyzed. The relative mixing index of the mini-fluidized beds is 3.07–9.55 times that of the particle-free tubes under the same conditions, and the mixing length and time are reduced by 45.11% ∼ 99.59%. When the bed-to-particle diameter ratio is 13.86, the optimal operating voidage is about 0.76, which corresponds to the maximum mixing effectiveness and mixing energy efficiency. The mixing enhancement of the mini-fluidized bed system was evaluated, which provides a theoretical basis for the new application of microstructures in mini-fluidized bed reactors.

In this work, the conveying flow pattern and pressure drop of spherical and non-spherical coarse particles in a horizontal pipe were measured experimentally. The experimental results show that when coarse particles are conveyed in stratified flow and sedimentation and dune formation, the rate of increase of pressure drop with superficial velocity is related only to the particles and not to the conveying conditions. The rate of increase of pressure drop with velocity is larger for spherical particles than for non-spherical particles in stratified flow, and the rate is smaller for spherical particles than for non-spherical particles in sedimentation and dune formation. The pressure drop varies linearly with the solid-gas ratio, and the slope of the linear relationship characterises the friction of the conveying pipe and the interaction parameters between the particles. The reduction in pressure drop for spherical particles is greater than that for non-spherical particles when the solid-gas ratio is increased by the same magnitude. In addition, to verify the experimental results of this work the data cited in the published literature were compared and the results were in good agreement. On the one hand, the variation rule of pressure drop with superficial velocity obtained in this investigation is an enrichment of the classical phase diagram. On the other hand, the experimental results are of guiding significance for the design and engineering application of coarse particle pneumatic conveying systems.

The study successfully demonstrated an eco-friendly approach for synthesizing mesoporous alumina and mesoporous silica from coal gangue, in line with green chemistry rules. By employing natural breakdown and increased dissolution of coal gangue through specific chemical treatments, along with optimal leaching conditions, this study achieved a dissolution efficiency of over 98% for aluminum. This process, which includes leaching, separation, simultaneous precipitation, selective dissolution, gel formation, and calcination, produced mesoporous alumina and mesoporous silica without the need for templates. The results presented that the synthesized mesoporous alumina and silica had purities of 98.81% and 99.08%, respectively. Additionally, the synthesized mesoporous alumina and silica had specific surface areas of 340.15 and 392.85 $m^2$/g, and average pore sizes of 7.27 and 3.25 nm, confirming the desirable physical properties of the synthesized γ-Al₂O₃ and SiO₂. These products offer a sustainable solution to environmental issues caused by coal accumulation, with promising applications across various industries.

Due to the decline in high-grade iron ore production, the utilization of low-grade iron ore, such as limonite, has become necessary. Limonite contains a significant amount of bound water, which requires a drying process prior to use. Excessive heat stress caused by the evaporation of bound and free water during the drying of limonite pellets can lead to pellet disintegration and adversely affect gas-solid reactions. In recent years, artificial neural network (ANN) has been developing continuously in the fields of modeling and intelligent control, and has been widely used. Many predecessors used artificial neural network model to study the drying process of natural organic matter, and analyzed the factors affecting the drying rate of organic matter. In this study, we employed big data analysis, specifically Multilayer Perceptron (MLP) artificial neural networks, to analyze the drying process of limonite pellets and successfully established a predictive drying model applicable to limonite pellets. The MLP artificial neural network demonstrated excellent fitting between predicted and experimental values, with a maxi-mum R2 value of 0.999. The artificial neural network for drying developed in this study provides technical guidance for industrial material drying, reduces the workload of manual measurements, and minimizes energy consumption.

The maximum efficiency inlet velocity (MEIV) serves as the upper limit for the inlet velocity that defines the separation efficiency in cyclone design and operation. In this paper, a combination of numerical and experimental methods is used to study MEIV. Experimental findings indicate that the MEIV is 22 m/s for a median particle size of 12.39 μm (coarse powder) and 35 m/s for a median particle size of 2.93 μm (fine powder). Meanwhile, the amount of escaped fine powder is reduced by 25% compared to that at an inlet velocity of 22 m/s. Computational fluid dynamics (CFD) simulations have shown that the inconsistency between tangential and axial velocity growth of inlet velocity with respect to various powder diameters can explain this phenomenon. As the inlet velocity increases, the peak axial velocity exhibits a stepwise increase. When the peak value remains constant, the peak width increases. This phenomenon is called stagnation of the axial velocity. During the axial velocity stagnation step, the residence time of back-mixed particles vary. In contrast, the tangential velocity increases linearly with the inlet velocity, resulting in an enhanced secondary separation of the inner vortex. Both factors hinder the escape of fine particles due to entrainment by a rapid upward airflow. The inlet velocity range corresponding to the stagnation step of the fine powder is larger than that of the coarse powder. Therefore, the MEIV of the fine powder is higher.

The deposition of graphite dust poses significant challenges to the helium turbines in high-temperature gas-cooled reactors. In this study, FLUENT, a Computational Fluid Dynamics (CFD) program was used with a discrete-phase model and a random-walk model to calculate the trajectories of particles (assumed spherical). Considering the interactions between particles and the wall as well as the resuspension effect of the fluid, a particle-deposition model was established and coupled to the flow-field calculations of blades with film cooling using user-defined functions. The influence of different deposition models, particle diameters, and blowing ratios on deposition were investigated. The results show rebounding and resuspending particles significantly affect the particle-deposition rate and its distribution. With increasing particle diameter, the deposition rate initially increases and then decreases. The influence of blowing ratio on deposition is complex; as the blowing ratio is increased, the deposition rate of small particles increases, while that of large particles decreases.

In this study, a numerical method, second-order moment of kinetic theory of granular flow for multi-type particles (SOM-KTGF-MP) is proposed. The SOM-KTGF is used for particle flow with higher concentration and high inertia where inter-particle collisions exist; however, the particle fluctuation is far from equilibrium to satisfy the Boussinesq hypothesis. The model, SOM-KTGF-MP, is derived here as an extension of SOM-KTGF for mono-sized particles to be applied to multi-type particles with different sizes, densities, and other properties. In SOM-KTGF-MP, the conservation equations of the volume fraction, mean velocity, and second-order moment of the fluctuating velocity of particles are solved for each type of particle species in the multi-type mixture. A binary mixture of particles in a simple shear flow was predicted using the SOM-KTGF-MP method. The result was in good agreement with the prediction made by the discrete molecular dynamics method, when considering the non-equipartition of particle velocity between particle species and the non-equipartition of energy between the normal components of the second-order moment of the fluctuating velocity of particles. The SOM-KTGF-MP method increased the fidelity of the prediction of the binary mixture flow of particles based on the kinetic theory.

The issue of wear failure in High-Pressure Abrasive Water Jet (HP-AWJ) nozzles is an unavoidable challenge, and studying methods to enhance and predict the effective lifetime of nozzles is worth deep exploration. This paper employs a CFD-DEM coupling numerical approach to investigate wear phenomena inside the HP-AWJ nozzle, aiming to capture the realistic particle wear and erosion failure issues at the focusing tube region, which is a high-wear area of the HP-AWJ nozzle. Furthermore, the study considers realistic particles and nozzle wall constitutive models, incorporating material properties into the physical model, and employs computer-aided design methods to reflect wear failure conditions at different time intervals in the inner wall of the focusing tube at the nozzle. The results demonstrate that the number of realistic particles and initial inlet velocity has no impact on the particle exit kinetic energy. However, the particle-wall restitution coefficient affects the average particle kinetic energy at the outlet in the AWJ nozzle. The equivalent model of the realistic particles reflects the influence of the particle roundness on particle kinetic energy, acceleration, and stress concentration variations in the nozzle. These variations further affect the particle erosion rate on the nozzle wall and the actual wear failure problems on the wall surface. Finally, by combining the proposed erosion and wear model, a representative erosion profile at the AWJ focusing tube location comparable to experimental results is obtained, and the wear depth of the focusing tube changing with time is also studied. The results and methodologies presented in this paper provide valuable guidance for controlling the effective service lifetime of the AWJ nozzle, improving machining efficiency, and extending the lifespan of the AWJ nozzle.

Centrifugal atomization by the rotating electrode process enables the production of powders with perfectly spherical particles. In this article, the history of centrifugal atomization and the selected recent innovations in this particle processing technology are discussed. Numerous materials and applications directly benefitting from this process are highlighted. Traditionally, this has included the alloys of titanium, tungsten, molybdenum and other metals, which continue to be widely applied in high technologies. More up-and-coming materials discussed include uranium-based fuels for nuclear fission reactors, neutron multipliers for fusion reactors, and magnetocaloric materials for converting gaseous into liquid hydrogen. In addition to the review of materials obtained for these distinct applications using the rotating electrode process, the fundamental principles governing the mechanism of formation of spherical particles constituting such materials are elaborated. Key limitations of the method are also discussed alongside the present and future directions for innovation inspired by the desire to solve them.

In this paper, the Morphological properties, Contact Mechanics, Adhesion, Roughness and Folding of Chronic Lymphocytic Leukemia (CLL) cells have been examined utilizing Atomic Force Microscopy (AFM). The results show that the morphology of the CLL cell is spherical, with an average surface roughness of 23.06 nm and 5.34% folds. Adhesion force and work of adhesion of CLL cells is in the range of 23.2 ± 15.6% nN and 1484.6 ± 13.1% nJ, respectively. DMT and BCP contact theories have been more accurate than Hertz theory in characterizing the mechanical contact behavior of CLL cells due to the consideration of adhesion properties. Also, applying the folding factor in the Hertz, DMT and BCP contact theories, for the same contact force predicts a larger contact radius and a smaller indentation depth, and the accuracy of its results has increased compared to the smooth state.