Powder Technology最新文献

This study investigates the complex dynamic characteristics of the flow field inside a disturbing rotary centrifugal air classifier through experimental analysis. To this end, micro-pressure sensors are employed to measure pressure signals in different spatial regions under various operating conditions. The analysis includes time-frequency characterization, complexity assessment, and multi-scale energy analysis. The time-domain fluctuation characteristics of the air classifier's pressure signal are closely tied to operating parameters, with the most intense pressure fluctuations occurring in the middle and back region of the air classifier. The loaded condition intensifies the fluctuations, with particle presence exacerbating low-frequency pressure variations and affecting the cyclone's vortex stability. Additionally, the internal installation of the screen cage structure exhibits maximum complexity and randomness in the internal flow field when R_f = 45 Hz, f = 0.4 kg/s, and β = 0°, showing higher randomness and reflecting fine-scale interactions between gas and particles. Conversely, larger scale characteristics are revealed by DET values in higher detail signal levels. Changes in operational parameters, such as perturbation frequency and feeding time, significantly affect the axial distribution of multi-scale energy in the air classifier, with a greater influence on pressure fluctuation at the macroscopic scale, indicating intensified turbulent behavior between gas and particles. This study reveals the influencing mechanisms of various operating parameters on the multiscale dynamic characteristics and complexity of the flow field inside the rotary centrifugal air classifier.

Most industrial vertical stirred mills contain a non-uniform set of grinding media sizes. However, this fact is often ignored in simulations, which mostly use monodispersed media. The paper explores the fundamental dynamics of vertical mills when using multiple sizes of grinding media, by using DEM simulation. Our results suggest that by including both large and small media, one may be able to optimise its performance in several manners. The energy going into the contacts can be increased by including a second size, leading to more effective grinding. Including smaller media can also reduce the power draw of the mill, increasing the efficiency and sustainability of the mill. Finally, the natural segregation between different sizes creates different types of collision which grind different particle sizes more effectively. Segregation leads to smaller media at the bottom, so continuous processes can be optimised for fine grinding by feeding from the top, where the larger media are. This further enables control of the resulting product specifications.

Deposition on heat exchange surfaces is an urgent problem to be solved to achieve efficient utilization of energy in thermal equipment. To mitigate deposition and the resultant heat attenuation, this work proposes a mixed tube bundle strategy of inserting attached cylinders behind the tube bundle, which can effectively meet the design requirements of high anti-deposition performance, high heat transfer efficiency, and low flow resistance. An integrated dynamic model for deposition is developed to elucidate the effect of ash particles on deposition, flow, and heat transfer characteristics. Based on the inverse distance weighting interpolation, a dynamic mesh smoothing technique is employed to simulate the evolving deposition layer on the heat transfer surface. In addition, the L₁₆(4³) orthogonal experimental design method is adopted to study the influence of the arrangement angle, diameter, and distance to the primary bundle of the attached cylinder on the overall performance, and determine the optimal scheme. The results show that deposition in the cases using the mixed tube bundle strategy has significantly decreased. The weakening effects of the attached cylinder on the deposition of small-medium particles and large-sized particles are due to the inhibition of vortex development in the gap of tube bundle and the deviation of the motion trajectory, respectively. The novel design exhibits the lowest deposition mass M_dep = 1.12 g and the best comprehensive performance PEC = 1.14 under the condition of the arrangement angle of 50°, the diameter of 10 mm, and the distance between the primary bundle of 5 mm. The obtained results can provide reference schemes and guidance for the optimization of the design of heat exchange equipment and accessory devices.

This study investigates the influence of various configurations of dipleg and dustbin structures on cyclone separator performance. For comparative analysis, the inverted cone dipleg which reported has the highest collection efficiency was employed, and six models were developed with varying dipleg-to-dustbin ratios while maintaining a constant total height. Unsteady simulations were conducted using the RSM model and the Eulerian-Lagrangian approach to analyze the flow dynamics and particle migration behaviors in cyclone separators. The increase in dipleg length significantly influenced flow behavior in both the dipleg and dustbin regions, initially resulting in increased flow complexity before transitioning to smoother and more regular patterns. Analysis of vortex frequency indicated a weakening back-mixing effect with increased dipleg length, further underscoring the impact of this parameter on cyclone performance. Quality factors under different particle size ranges are proposed to compare the separation efficiency and pressure drop of different models, providing a reference for the selection of cyclone in different application scenarios.

This study investigates the impact of sugar content on the physicochemical properties of oven-dried dates powder from four distinct cultivars—Ajwa, Safawi, Sukkary, and Medjool. The drying process reduced moisture content by approximately 55% (Ajwa), 58% (Safawi), 76% (Sukkary), and 60% (Medjool). Quantification of sugars using High Performance Liquid Chromatography equipped with refractive index detector (HPLC-RI) revealed varying sugar compositions, with Ajwa, Safawi, and Sukkary containing a mix of fructose, glucose, sucrose, maltose, and lactose, while Medjool lacked lactose. Sukkary date powder exhibited superior flowability properties due to lower sugar and moisture content, meeting industry standards, although it displayed a higher tendency to cake compared to white and coconut sugars. Other physicochemical characterisation (pH, colour properties L*(lightness), a*(redness/greenness), b* (blueness/yellowness) values, hygroscopicity, solubility, morphology and chemical structure of all date sugar were also explored in comparison with commercial sugars (white sugar and, brown sugar and coconut sugar) as controls. Notably, Sukkary date powder emerged as a promising cultivar for production, offering reduced clumpiness and stickiness in comparison to Ajwa, Safawi, and Medjool date powders. These findings provide valuable insights for food manufacturers, formulators, and researchers interested in using Sukkary date powder in various foods. The potential use of Sukkary as a sugar substitute or carbohydrate source, suitable for both normal and diabetic individuals, underscores its versatility and highlights avenues for innovation in the food industry especially in confectionary, bakeries, beverages, snack foods or other natural, health-oriented food industries.

Reactive aluminium (Al) powders, which are used in propellants and explosives, require the active support of strong oxidizers to break Al oxide layer and better surface thermochemical reaction. Considering this, current work demonstrates the improved ignition and combustibility of the recycled Al powder modified with various fluorinated and polyphenolic interfacial layers and reactive metals. The better activity was owned by the Al@PD/TA/Fe sample. The DSC result of the Al@PD/TA/Fe sample revealed the oxidation of PVDF at 341.56 °C and surface oxidation of Al at a temperature of 426.81 °C. The decomposition of fluoropolymer at lower temperature facilitated the prompt surface oxidation of Al followed by efficient rupture of the oxide layer which promoted the pre-ignition reaction of Al. Based on the results, combustion mechanism has been proposed. The ignition test of the Al@PD/TA/Fe sample has shown the rapid ignition luminous streaks and claims its potential candidature for solid fuel application.

A coarse-grained (CG) approach, which can significantly facilitate large-scale modelling of particle systems, was proposed for predicting the surface erosion in an elbow pipe induced by dilute gas-particle flow. In the approach, the particle sizes and forces such as gas-particle interactions are scaled in terms of a CG ratio. A particle-level Shear Impact Energy Model (SIEM) is applied to calculate the erosion rate. The accuracy of the CG approach is evaluated extensively for different particle concentrations and tube diameters. The CG approach is found to work satisfactorily when suitable fluctuation velocities are used at the inlet of the tube. The reason is that the fluctuation velocities keep the kinetic energy of particles conservative within the elbow. An equation was provided for determining the magnitude of the fluctuation velocity in CG modelling of the elbow pipe and its universality is tested under different coarse-grained ratios and particle concentrations.

In this paper, two types of Ni-Cr bearing composite burdens including SP1 (79% Ni-bearing sinter and 21% Cr-bearing oxide pellets) and SP2 (84% Ni-bearing sinter and 16% Cr-bearing pre-reduced pellets) were used for the more efficient preparation of high-Cr ferronickel. Based on the metallurgical performance characterization, thermodynamic analysis and smelting parameters optimization, the qualified high-Cr ferronickel were prepared by the utilization of the Ni-Cr bearing composite burdens. The recovery rates of iron, chromium and nickel exceed 95%, 90% and 98% whereas their grades are 85.56–85.88%, 7.82–8.02% and 1.59–1.62%, respectively. Compared with SP1, SP2 possesses lower smelting duration, which indicates the appropriate proportioning of Cr-bearing pre-reduced pellets is beneficial for the smelting process. The obtained high-Cr ferronickel consisting of (Fe, Cr)₃C and (Fe, Cr)₇C₃ can be used as a low-cost substitute for the conventional raw materials of 200 or 300 series of stainless steel.

Microscale experimental techniques are challenging in terms of test time, sample preparation, and resolution. It is also difficult for molecular dynamics (MD) to overcome spatial and temporal limitations. Wyoming sodium montmorillonite was used in this study. Based on the Gay-Berne potential (GB), the unloading properties of clay aggregates under different environmental conditions were simulated using coarse-grained molecular dynamics (CGMD) method. The results showed that for each case, the deformation was closely related to the distribution of the stacks. In particular, the relationship between the total number of stacks and void ratio followed the Boltzmann distribution. At the same time, it was found that the stress states in different cases during unloading depend on the particle orientation. For one-dimensional unloading, the particle arrangements exhibited significant anisotropy, leading to a smaller vertical rebound. Owing to the isotropic compression at 1 atm and lateral confinement, the lateral pressure coefficient (k) is >1 in the atmospheric environment. In contrast, limited lateral expansion caused k to be smaller than 1 in a vacuum. With decreasing confining pressure, a linear increase in the void ratio was observed. During this process, the number of small-sized stacks gradually decreased, accompanied by an increase in the number of large-sized stacks. From 100 MPa to 1 MPa, the longer the unloading path, the smaller the rebound. In the range of 0.1–0.7 MPa, the clay configurations reached equilibrium and the unloading paths had no obvious effects on the distribution of stacks. This work demonstrates the validity of the GB potential model, which provides a basis for bottom-up mechanical prediction of the hierarchical structure of Na-montmorillonite particles.

The optimal reconstruction parameters of spherical harmonic (SH) series for the aggregates with different morphologies and sizes were not clear. In this paper, manufactured aggregates with different sizes (1.18–2.36 mm, 2.36–4.75 mm, 4.75–9.50 mm), and natural aggregate with size >1.18 mm were scanned using the digital light projection (DLP), and reconstructed using SH series. The effect of maximum number of SH functions (N) used in the reconstruction series and the number of terms in the Gaussian quadrature (G) used for solving the SH expansion coefficients on the reconstruction errors were studied. The optimal reconstruction parameters for different particle sizes and morphologies were proposed, via a derived relationship between N and G. The reconstruction errors decreased when the N and G values increased. The relationship between N and G was derived to be G ≥ 1.84 N + 3.60, which is probably caused by the issue of the algebraic precision of the Gaussian integral.