Ellipsoidal Shape Research Articles

Study on Cavitation Bubble Characteristics in Centrifugal Pump Based on Image Recognition

In this paper, a cavitation bubble in the centrifugal pump cavitation phenomenon was observed in the analysis and research to explore the characteristics of a cavitation bubble in a centrifugal pump. Through the construction of a visualization centrifugal pump test platform and the observation of a high-speed camera, an image processing method was used to extract the characteristics of the cavitation bubble in the captured results, and the characteristics of the cavitation bubble in the centrifugal pump were analyzed and studied in a quantitative way. The results show that the shapes of the cavitation bubbles in a centrifugal pump can be simplified approximately into an ellipsoid shape, more than 75% of the bubbles have a length–diameter ratio between 1 and 2, and the distribution is relatively uniform. Different working conditions affect the size of the cavitation bubble but have little effect on the shape. The average size of the cavitation bubble under different working conditions was calculated by data fitting. This method, which combines high-speed imaging technology and image processing technology, is capable of observing the behavioral characteristics of cavitation bubbles in centrifugal pump cavitation flow both in detail and intuitively. The new method is provided to describe quantitatively the shapes and sizes of bubbles. It is of great significance in understanding the movement characteristics and manifestations of bubbles during a centrifugal pump’s operation and in the further study of the micro mechanisms of the negative effects of cavitation on equipment performance.

Statistical 3D morphology characterization of vaterite microspheres produced by engineered Escherichia coli

Hollow vaterite microspheres are important materials for biomedical applications such as drug delivery and regenerative medicine owing to their biocompatibility, high specific surface area, and ability to encapsulate a large number of bioactive molecules and compounds. We demonstrated that hollow vaterite microspheres are produced by an Escherichia coli strain engineered with a urease gene cluster from the ureolytic bacteria Sporosarcina pasteurii in the presence of bovine serum albumin. We characterized the 3D nanoscale morphology of five biogenic hollow vaterite microspheres using 3D high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) tomography. Using automated high-throughput HAADF-STEM imaging across several sample tilt orientations, we show that the microspheres evolved from a smaller more ellipsoidal shape to a larger more spherical shape while the internal hollow core increased in size and remained relatively spherical, indicating that the microspheres produced by this engineered strain likely do not contain the bacteria. The statistical 3D morphology information demonstrates the potential for using biogenic calcium carbonate mineralization to produce hollow vaterite microspheres with controlled morphologies. Statement of significanceThe nanoscale 3D structures of biomaterials determine their physical, chemical, and biological properties, however significant efforts are required to obtain a statistical understanding of the internal 3D morphology of materials without damaging the structures. In this study, we developed a non-destructive, automated technique that allows us to understand the nanoscale 3D morphology of many unique hollow vaterite microspheres beyond the spectroscopy methods that lack local information and microscopy methods that cannot interrogate the full 3D structure. The method allowed us to quantitatively correlate the external diameters and aspect ratios of vaterite microspheres with their hollow internal structures at the nanoscale. This work demonstrates the opportunity to use automated transmission electron microscopy to characterize nanoscale 3D morphologies of many biomaterials and validate the chemical and biological functionality of these materials.

Bubbly flows in a column with submerged hollow fiber membranes

Experiments of bubbly flows in a column with submerged hollow fiber membranes are carried out to discuss the relation between bubbly flow characteristics and fouling control. Two kinds of liquids, water and xanthan gum-water solution (XG-W), are used as the liquid phases. The relaxation rates of membranes are set at 0.0 or 0.5%. The number of small bubbles with ellipsoidal shapes in water are larger than that in XG-W, while large bubbles with spherical cap shapes are remarkably observed in XG-W in spite of the presence of membranes. The rate of large bubbles is enhanced in XG-W due to bubble coalescence. The gas holdup in water is higher than that in XG-W. The gas holdup becomes higher due to the presence of membranes and membrane relaxation in both water and XG-W. For discussion on fouling control due to bubbly flows, experiments are carried out to remove pseudo sludge attached to hollow fiber membranes. The relaxation of membranes enhances the removal rate of pseudo sludge. The mean removal rate, which is the mean value of the removal rate of each membrane, increases with increasing the gas holdup. This relation is well expressed by a linear regression in the present experimental range regardless of the liquid property and membrane relaxation, that is, the gas holdup has a prospect of an indicator for estimating fouling probability.

New method of chemical synthesis for nanostructured Nd-Fe-B alloy

A new method of chemical synthesis has been developed for the nanostructured Nd-Fe-B alloy using nanoparticles of Nd2O3, Fe2O3, and Fe3BO6 powders. The nanoparticles of Nd2O3, Fe2O3, and Fe3BO6 were obtained through chemical precipitation followed by calcination. The Nd2O3 nanoparticles have a rod-like shape with a diameter of 28 nm and a length of 118 nm. The α-Fe2O3 nanoparticles have an ellipsoidal shape with an average diameter of 55 ± 11 nm. Additionally, a powder mixture of nanoparticles containing 74.4 wt% α-Fe2O3 and 25.6 wt% Fe3BO6 was obtained, and the particles exhibit an irregular shape with an average diameter of 50 ± 10 nm. A mechanism for the formation of the nanostructured Nd-Fe-B alloy from the Nd2O3, Fe2O3, and Fe3BO6 nanoparticles was proposed. It was found that during the initial stage of the reductive-diffusion process, nanopowders of NdFeO3, NdBO3, and α-Fe2O3 are formed. In the second stage of the reductive-diffusion process, nanopowders consisting of phases of 36.7 wt% Nd2Fe14B, 10.9 wt% α-Fe, and 52.4 wt% CaO are formed. After removing CaO, the obtained nanostructured Nd-Fe-B alloy consists of 76.1 wt% Nd2Fe14B, a hard magnetic phase, and 23.9 wt% α-Fe, a soft magnetic phase. The average particle size of the nanostructured Nd-Fe-B alloy is 110 ± 35 nm. The nanostructured Nd-Fe-B alloy powders exhibit the following magnetic characteristics: coercive force (Hc) of 3295 Oe, saturation magnetization (Ms) of 132.01 A·m2/kg, and residual magnetization (Mr) of 99.53 A·m2/kg.

Simulating droplet distribution characteristics for sprinkler irrigation with a modified ballistic model

The ballistic model, with its high computational efficiency and small test workload, is an effective method to simulate the distribution of spray droplets. It can be employed to solve the problems of oversimplifying the droplet crushing process and motion shape and ignoring the droplet energy characteristics in the equivalent droplet indicator in the existing model assumptions. Based on the law of the motion of sprinkler irrigation water flow, the model assumption of continuous motion and segmental fragmentation of the jet is proposed in the current study. Ellipsoidal droplet shape parameters were introduced to construct the equations of the motion of sprinkler irrigation water flow in the jet and droplet stages, respectively. The critical conditions for large droplet separation and correction drag coefficient for small droplets are defined and solved, and the calculation formulas based on the energy-weighted equivalent droplet indicators were derived. The accuracy of the model was verified using 50PYC, ZY-2, and HY50 nozzles, and the modified model was compared with Fukui’s and Li’s models. The effects of working pressure, nozzle diameter, nozzle elevation angle, and installation height on the droplet landing distance, velocity, and angle at the end of the spray range were investigated. The results showed that: (1) The mean absolute error (MAE) and root-mean-square error (RMSE) of droplet landing distance, velocity, and angle under different working conditions simulated by the modified model were smaller than those obtained using Fukui’s and Li’s models, showing better simulation accuracy. Considering the simulated values of droplet landing distance, velocity, and angle of the 50 PYC nozzle (nozzle diameter of 22 mm and working pressure of 0.35 MPa) as an example, the accuracy of the modified model was improved by 72.86 % and 53.45 % (landing distance), 35.86 % and 70.57 % (landing velocity), 42.10 % and 67.66 % (landing angle) compared with the Fukui’s and the Li’s models, respectively. (2) Fukui’s and Li’s models demonstrate higher accuracy in simulating the droplet landing distance of the ZY-2 nozzle with a smaller nozzle diameter (7 mm) than in simulating the HY50 and 50PYC nozzles; (3) The changes in nozzle operating pressure, nozzle diameter, and nozzle elevation angle exert the greatest effect on the droplet landing distance, landing velocity, and landing angle, respectively. This study provides a novel idea for using the ballistic model to simulate the spray droplet distribution.

Physicochemical properties of different size fractions of potato starch cultivated in Highland China

Location influences the properties of potato starch. Potato starch granules cultivated in highland of China were separated into three fractions according to the sedimentation time: large- (∼81 μm, large fraction potato starch, LFPS), medium- (∼28 μm, medium fraction potato starch, MFPS), and small-size (∼15 μm, small fraction potato starch, SFPS) fractions. SFPS showed a spherical shape, MFPS showed an ellipsoid shape and LFPS showed an elongated shape. The three fractions showed the similar XRD patterns, while the relative crystallinity decreased with the decrease of granule size (LFPS 23.61%, MFPS 20.74% and SFPS 20.48%). The water solubility was positively corelated with the granule size, while the swelling power showed a negative relationship with the granule size. For the rheological properties, all the three fractions showed a shear-shinning behavior; and SFPS had the highest peak temperature. However, the MFPS showed the lowest storage modulus during the temperature sweep. The granule size didn’t influence the nutritional properties of potato starch and LFPS had the highest slowly digestible starch (SDS) (83.77%) and resistant starch (RS) (13.66%) contents. Some of the properties are different from the previous studies.

The Simulation of Dielectric Barrier Discharge for Breakdown Voltage in Starch Modification

This paper presents the simulation results for dielectric barrier discharge (DBD) at atmospheric pressure in argon gas for different relative permittivity, granule shape, thickness layer, and granule diameter measurements for starch on the breakdown voltage. DBD is commonly utilized to generate cold plasma for starch modification. The electric field was computed using COMSOL Multiphysics 5.3a software. The breakdown voltage was calculated employing Paschen’s law for this electric field. The voltage was found according to the breakdown criterion for gap distance 0.2–1.0 cm, and then the Paschen curve could be plotted. The results show that the top electrode of the plasma system may be replaced with the parallel plate electrode by a mesh electrode with a bigger mesh size to achieve a lower breakdown voltage. In addition, increasing the relative permittivity and decreasing the thickness layer can reduce the applied voltage for plasma formation. When compared to the sphere and ellipsoid shapes, starch with a polyhedral granule shape requires a significantly lower voltage for breakdown. The starch granule diameter does not affect the breakdown voltage. These findings can be utilized to determine the optimal breakdown voltage for each type of starch modification, contributing to the construction of a high-efficiency plasma production system for starch modification.

Thermal ablation with configurable shapes: a comprehensive, automated model for bespoke tumor treatment

BackgroundMalignant tumors routinely present with irregular shapes and complex configurations. The lack of customization to individual tumor shapes and standardization of procedures limits the success and application of thermal ablation.MethodsWe introduced an automated treatment model consisting of (i) trajectory and ablation profile planning, (ii) ablation probe insertion, (iii) dynamic energy delivery (including robotically driven control of the energy source power and location over time, according to a treatment plan bespoke to the tumor shape), and (iv) quantitative ablation margin verification. We used a microwave ablation system and a liver phantom (acrylamide polymer with a thermochromic ink) to mimic coagulation and measure the ablation volume. We estimated the ablation width as a function of power and velocity following a probabilistic model. Four representative shapes of liver tumors < 5 cm were selected from two publicly available databases. The ablated specimens were cut along the ablation probe axis and photographed. The shape of the ablated volume was extracted using a color-based segmentation method.ResultsThe uncertainty (standard deviation) of the ablation width increased with increasing power by ± 0.03 mm (95% credible interval [0.02, 0.043]) per watt increase in power and by ± 0.85 mm (95% credible interval [0, 2.5]) per mm/s increase in velocity. Continuous ablation along a straight-line trajectory resulted in elongated rotationally symmetric ablation shapes. Simultaneous regulation of the power and/or translation velocity allowed to modulate the ablation width at specific locations.ConclusionsThis study offers the proof-of-principle of the dynamic energy delivery system using ablation shapes from clinical cases of malignant liver tumors.Relevance statementThe proposed automated treatment model could favor the customization and standardization of thermal ablation for complex tumor shapes.Key points• Current thermal ablation systems are limited to ellipsoidal or spherical shapes.• Dynamic energy delivery produces elongated rotationally symmetric ablation shapes with varying widths.• For complex tumor shapes, multiple customized ablation shapes could be combined.Graphical

Early Paleozoic ductile deformation of the South China Block: the polyphase shear zones in the eastern Jiangnan belt

Three parallel east–west-trending shear zones are components of the polyphase shear zones in the eastern Jiangnan belt. The meso- and microstructural characteristics and the estimates of deformation temperatures, vorticities and geochronology of these shear zones provide significant information regarding the tectonic evolution of the South China Block (SCB) during the early Paleozoic. Most shear sense indicators (e.g. asymmetric folds, S-C fabrics and rotating porphyroclasts) reveal that the kinematics were characterized by east–west dextral shear. Finite strain measurements indicate an oblate strain ellipsoid shape with S-type and SL-type tectonites. The rotated rigid porphyroclasts and Mohr circle methods yield vorticity ( Wk ) values of 0.58–0.80 and 0.66–0.89, respectively, indicating that the flow was generally shear-dominated with almost equal proportions of simple and pure shear. Both mineral deformation thermometers and quartz c -axis fabrics indicate that the deformation occurred at medium temperature conditions of 400–550°C. Combined with our new age and regional geological data, the east–west-trending shear zones might represent an increment of deformation during the last period of the early Paleozoic orogeny in the SCB.

Microstructure Evolution and Deformation Mechanism of Ti‐55531 Alloy During Hot‐Rolling Process

Ti‐55531 alloy is a novel near‐β‐Ti alloy, which has promising application potential as critical aircraft components due to its outstanding mechanical properties. In this work, it is aimed to tailor the microstructure and mechanical properties of Ti‐55531 alloy by hot‐rolling in α + β‐phase field. In experimental results, it is indicated that an increasing number of α lamellae becomes globular or ellipsoidal shape with the increase of rolling reduction. As a result, the strength and elongation of the rolled samples continually increase. Lath‐like substructures are observed inside some residual lamellar α after 20% rolling reduction. Nearly all lath‐like substructures have their habit plane corresponding to (100)α and exhibit the orientation relationship (OR) of [0001]HCP //[001]FCC, [20]HCP //[]FCC, and (100)HCP //(FCC with α phase. At high rolling reductions, the face‐centered cubic (FCC) substructures disappeared. Instead, {101} twin structures are frequently observed in lamellar α grains, indicating that both {101} twinning and martensitic transformation can be activated in Ti‐55531 alloy to accommodate the applied rolling deformation. To the authors’ knowledge, such stress‐induced martensitic transformation has not been reported before in Ti‐55531 alloy. Therefore, the findings in this work should advance the understandings on the deformation behavior and mechanism in this alloy.

Characterization of pore space in Permo-Triassic sandstone from SW-Germany using the anisotropy of magnetic susceptibility

Pore space in siliciclastic rocks is one of the most important petrophysical properties in geothermal and hydrocarbon reservoir rock characterization. We used the anisotropy of magnetic susceptibility (AMS) of ferrofluid-impregnated Permo-Triassic sandstones of different Buntsandstein and Rotliegend facies as a proxy for pore space anisotropy and preferred flow direction as a case study for reservoir characterization. We compared the calculated ferrofluid porosity (2–21%) with He porosity (2–26%) and permeability (0.002–214 mD) and described the sediment microstructure using petrographic point-counting analysis. For water- and oil-based ferrofluid impregnation, we observed a positive correlation with He porosity and mass and susceptibility impregnation efficiency were used to control the quality of the impregnation process. Triaxial to oblate magnetic rock fabrics were mostly mimicked by the magnetic pore fabrics, except for some of the water-based ferrofluid impregnated samples, where magnetic ellipsoid shapes changed from oblate to prolate. AMS of the unimpregnated sandstones reflects well defined primary sedimentary to diagenetic fabrics with grain imbrication and cross bedding along with more laminated sedimentary structures. Deviation in ferrofluid-impregnated AMS axes orientation can be related either to the low anisotropy < 1.07 in sandstones from the Lower and Upper Buntsandstein, or the low impregnation efficiency. The mimicry is mostly better when the magnetic susceptibility of the sandstone is higher due to a higher concentration of phyllosilicates while micro-porosity is controlled by the clay fabric. A comparison of sediment petrography with magnetic pore fabrics suggests that the pore space is controlled by the bedding of the sandstones with mostly no preferred flow direction within the bedding plane.Graphical

An investigation into the morphological distribution of the temperature field in loose media and its underlying principles of evolution

The spontaneous combustion of coal in goaf has important implications for the safe mining of working faces; hence, it is crucial to prevent and control such occurrences. Here, we establish an experimental system to investigate the morphological distribution, evolution, and migration process of the temperature field of the thermal core area in systems with various particle sizes. Furthermore, we propose a high-temperature-region inversion method based on the morphological evolution model of the temperature field. Our experimental results demonstrate that particle size is a critical factor influencing the temperature field morphology under a given heating condition. During the heating stage, the isothermal surface within the thermal core area forms an ellipsoidal shape, with a transverse section comprising concentric circles, and a longitudinal section comprising ellipses. During the heat dissipation stage, the isothermal surface of the small-particle-size system encircles the thermal core area from the upper direction downwards, while the isothermal surface of the large-particle-size system encircles the thermal core area from the lower direction upwards. Moreover, the thermal core area of the large-particle-size system migrates upwards, while the thermal core area of the small-particle-size system migrates a shorter distance. Finally, we used a geometrically simplified temperature field in loose media to propose a high-temperature-region inversion method, which was verified by experiments. This study is crucial for understanding the distribution and evolution of temperature fields in loose media and predicting the formation and development of high-temperature regions.

On the Thermoelastic Influence of Fluid-Gas Phase Transition Pressure on the Closed Structural Storage Container

The current paper presents a finite element method (FEM) axisymmetric solution based on commercial software for an isotropic closed-ended container filled with fluid, located in the triple point phase (liquefied gas) while being converted into gas through a phase transition to critical point phase by a simultaneously rapid change of pressure and temperature to their critical values. The whole chemical process will be simulated through thermo-elastic analysis that is controlled by temperature-displacement dynamic coupling and subjected to step function boundary conditions alongside liquefied triple point initial conditions. In the process, the maximum principal stresses will be determined and illustrated as dependent on the container thickness. In the process, investigation will be carried out for prominent parameters, like, container hollow geometry type (spherical, ellipsoidal, and cylindrical) and raw material of the container. Commercial software solution calibration against existing literature solutions has been performed. Also, the solution accuracy was examined by element size mesh analysis to be coherent. In conclusion, the best materials to use were Molybdenum TZM and Tungsten while the preferred shape is the ellipsoidal shape. However, a typical vessel that is still durable with sufficient thermal strength for gas storage purposes is a cylinder body container with spherical ended cups made from Aluminum 6061 T6.

Asymmetries in random motions of neutral hydrogen gas in spiral galaxies

Context. The velocity dispersion ellipsoid of gas in galactic discs is usually assumed to be isotropic. Under this approximation, no projection effect occurs in the random motions of gas, as traced by the line-of-sight velocity dispersion. However, it has been recently shown that random motions of the neutral hydrogen gas of the Triangulum galaxy (M 33) exhibit a bisymmetric perturbation which is aligned with the minor axis of the galaxy, suggesting a projection effect. Aims. To investigate if perturbations in the velocity dispersion of nearby discs are comparable to those of M 33, the sample is extended to 32 galaxies from The H I Nearby Galaxy Survey (THINGS) and the Westerbork H I Survey of Spiral and Irregular Galaxies (WHISP). Methods. We studied velocity asymmetries in the disc planes by performing Fourier transforms of high-resolution H I velocity dispersion maps corrected for beam-smearing effects, and we measured the amplitudes and phase angles of the Fourier harmonics. Results. In all velocity dispersion maps, we find strong perturbations of first, second, and fourth orders. The strongest asymmetry is the bisymmetry, which is predominantly associated with the presence of spiral arms. The first order asymmetry is generally orientated close to the disc major axis, and the second and fourth order asymmetries are preferentially orientated along intermediate directions between the major and minor axes of the discs. These results are evidence that strong projection effects shape the H I velocity dispersion maps. The most likely source of systematic orientations is the anisotropy of velocities, through the projection of streaming motions that are stronger along one of the planar directions in the discs. Moreover, systematic phase angles of asymmetries in the H I velocity dispersion could arise from tilted velocity ellipsoids, that is when the velocities are correlated. We expect a larger incidence of correlation between the radial and tangential velocities of H I gas with |ρRθ|∼0.6, which could be tested against the kinematics of the youngest stellar populations of the Milky Way. Conclusions. H I velocity dispersions cannot be considered devoid of projection effects. The systematic orientations of asymmetries can be explained by the projection of unresolved streaming motions mainly arising from spiral arms. Our methodology is a powerful tool to constrain the dominant direction of streaming motions and thus the shape of the velocity ellipsoid of H I gas, which is de facto anisotropic at the angular scales probed by the observations. The next step is to study the shape of the velocity ellipsoids of molecular and ionised gas and their link with galaxy mass and/or morphology, in addition to extending the sample size.

Polynomial inclusions: Definitions, applications, and open problems

Predictive modeling in physical science and engineering is mostly based on solving certain partial differential equations where the complexity of solutions is dictated by the geometry of the domain. Motivated by the broad applications of explicit solutions for spherical and ellipsoidal domains, in particular, the Eshelby’s solution in elasticity, we propose a generalization of ellipsoidal shapes called polynomial inclusions. A polynomial inclusion (or p-inclusion for brevity) of degree k is defined as a smooth, connected and bounded body whose Newtonian potential is a polynomial of degree k inside the body. From this viewpoint, ellipsoids are identified as the only p-inclusions of degree two; many fundamental problems in various physical settings admit simple closed-form solutions for general p-inclusions as for ellipsoids. Therefore, we anticipate that p-inclusions will be useful for applications including predictive materials models, optimal designs, and inverse problems. However, the existence of p-inclusions beyond degree two is not obvious, not to mention their explicit algebraic parameterizations.In this work, we explore alternative definitions and properties of p-inclusions in the context of potential theory. Based on the theory of variational inequalities, we show that p-inclusions do exist for certain polynomials, though a complete characterization remains open. We reformulate the determination of surfaces of p-inclusions as nonlocal geometric flows which are convenient for numerical simulations and studying geometric properties of p-inclusions. In two dimensions, by the method of conformal mapping we find an explicit algebraic parameterization of p-inclusions. We also propose a few open problems whose solution will deepen our understanding of relations between domain geometry, Newtonian potentials, and solutions to general partial differential equations. We conclude by presenting examples of applications of p-inclusions in the context of Eshelby inclusion problems and magnet designs.

Validation of HiG-Flow Software for Simulating Two-Phase Flows with a 3D Geometric Volume of Fluid Algorithm

This study reports the development of a numerical method to simulate two-phase flows of Newtonian fluids that are incompressible, immiscible, and isothermal. The interface in the simulation is located and reconstructed using the geometric volume of fluid (VOF) method. The implementation of the piecewise-linear interface calculation (PLIC) scheme of the VOF method is performed to solve the three-dimensional (3D) interface transport during the dynamics of two-phase flows. In this method, the interface is approximated by a line segment in each interfacial cell. The balance of forces at the interface is accounted for using the continuum interfacial force (CSF) model. To solve the Navier–Stokes equations, meshless finite difference schemes from the HiG-Flow computational fluid dynamics software are employed. The 3D PLIC-VOF HiG-Flow algorithm is used to simulate several benchmark two-phase flows for the purpose of validating the numerical implementation. First, the performance of the PLIC implementation is evaluated by conducting two standard advection numerical tests: the 3D shearing flow test and the 3D deforming field test. Good agreement is obtained for the 3D interface shape using both the 3D PLIC-VOF HiG-Flow algorithm and those found in the scientific literature, specifically, the piecewise-constant flux surface calculation, the volume of fluid method implemented in OpenFOAM, and the high-order finite-element software FEEL. In addition, the absolute error of the volume tracking advection calculation obtained by our 3D PLIC-VOF HiG-Flow algorithm is found to be smaller than the one found in the scientific literature for both the 3D shearing and 3D deforming flow tests. The volume fraction conservation absolute errors obtained using our algorithm are 4.48×10−5 and 9.41×10−6 for both shearing and deforming flow tests, respectively, being two orders lower than the results presented in the scientific literature at the same level of mesh refinement. Lastly, the 3D bubble rising problem is simulated for different fluid densities (ρ1/ρ2=10 and ρ1/ρ2=1000) and viscosity ratios (μ1/μ2=10 and μ1/μ2=100). Again, good agreement is obtained for the 3D interface shape using both the newly implemented algorithm and OpenFOAM, DROPS, and NaSt3D software. The 3D PLIC-VOF HiG-Flow algorithm predicted a stable ellipsoidal droplet shape for ρ1/ρ2=10 and μ1/μ2=10, and a stable cap shape for ρ1/ρ2=1000 and μ1/μ2=100. The bubble’s rise velocity and evolution of the bubble’s center of mass are also computed with the 3D PLIC-VOF HiG-Flow algorithm and found to be in agreement with those software. The rise velocity of the droplet for both the ellipsoidal and cap flow regime’s is found, in the initial stages of the simulation, to gradually increase from its initial value of zero to a maximum magnitude; then, the steady-state velocity of the droplet decreases, being more accentuated for the cap regime.

Composition and Textural Characteristics of Char Powders Produced by Thermomechanical Processing of Sunflower Seed Husks

The paper presents the results of experimental studies on the production of fine char powder from sunflower seed husks by a novel method of thermomechanical treatment with pulsed shock waves and supersonic jets of the mixture of ultra-superheated (above 2000 °C) steam and carbon dioxide, as well as the results of examination of the produced char powder in terms of its chemical, phase, and granulometric composition and structural, morphological, and texture characteristics. The objective of the research is to explore the possibility of using the resulting char powder as a sorption-active material for organic substances. It is shown that the obtained char particles and their agglomerates have an average size of 20–30 nm and 12–24 µm, respectively, have the shape of disks and ellipsoids, consist mainly of amorphous carbon (up to 56 wt%) and oxygen (up to 42 wt%), and have a specific surface area of 1.1–1.7 m2/g. It is concluded that such a char powder can be used as an absorbent for organic substances when dried and deagglomerated.

Mesoscopic pore characteristics analysis of aged bridge concrete based on X-ray computed tomography

The characteristics of mesoscopic pores in concrete bridges have significant influence on structural mechanical properties. In this study, 18 core specimens, taken from three decommissioned concrete bridges serving for about 25 years, were investigated using X-ray computed tomography (X-ray CT). After segmentation and 3D reconstruction with CT scanning images, the spatial characteristics for the porosity, volume, and shape of the concrete mesoscopic pores were analysed. The mesoscopic porosity decreases with the increase of concrete strength. The logarithm of the pore volume obeyed the Gumbel extreme value distribution, whose location and scale parameters had obvious bilinear degradation with depth. Ellipsoidal approximation was employed to precisely characterise the individual pore structure, and the Gaussian copula function could describe the joint distribution among the pore shape parameters. It was found that correlation coefficients of ellipsoidal shape parameters remained stable with depth. The proposed model quantitatively describes the mesoscopic pores in decommissioned concrete bridges and can shed certain light on concrete pore simulation.

Laser ignition and flame propagation of methanol-air mixture in a constant volume combustion chamber

ABSTRACT The combustion performance of laser-ignited methanol-air mixture in a constant volume combustion chamber was investigated using the Schlieren photography technique. The experimentation was conducted at 5, 7, 9, and 11 MPa fuel injection pressure and 363 K initial chamber temperature using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser of 1064 nm wavelength. The gasoline direct injection (GDI) system was used for injecting the fuel at different pressures inside the chamber. The laser beam is focused into the chamber using a 150 mm focal length lens, and laser energy of 200 mJ was used for all experimentation. The Schlieren system was used for capturing flame propagation of methanol-air mixture for different equivalence ratios. The pressure-time history for equivalence ratio (ϕ) of 0.8, 0.9, and 1.0 was plotted and analyzed at different chamber filling pressures. Flame propagation was found faster for ϕ of 1.0 due to higher laminar velocity than 0.8 and 0.9. Flame visualization showed that the flame attains the ellipsoid shape during the early stage of ignition. It generates two lobes in the vertical direction and then again expands in a horizontal direction toward the ignition source. For all equivalence ratios, the flame propagation toward the incoming laser source (X-) was observed faster compared to the flame propagation in the direction and perpendicular to the laser beam direction. For all equivalence ratios, higher laminar flame speed was observed at 5 MPa injection pressure; however, it decreases as the injection pressure increases. At ϕ of 1.0 and 11 MPa injection pressure, the maximum peak pressure of 0.67 MPa and combustion duration of 19.3 ms were noted. At 9 MPa injection pressure and ϕ of 1.0, the peak pressure and combustion duration was found as 0.61 MPa and 19.4 ms, respectively. At ϕ of 0.8, the peak pressure and combustion duration were observed 0.27 MPa with 34.6 ms duration and 0.47 MPa with 36.9 ms duration at 5 MPa and 11 MPa injection pressures, respectively.

Polarization Signature of Companion-fed Supernovae Arising from BH–NS/BH Progenitor Systems

The formation of black hole–neutron star (BH–NS) or BH–BH systems may be accompanied by special supernova (SN) signals, due to the accretion feedback from the companion BH. The additional heating, which is mainly attributed to the Blandford–Payne mechanism, would disrupt the isotropic nature of the luminosity distribution on the surface of the SN ejecta, leading to the appearance of polarization. Here we develop a three-dimensional Monte Carlo polarization simulation code to conduct simulations for these special SNe. We find that the maximum polarization level of ∼2% occurs at the peak time of SN emission in the “close-binary” scenario, while in the “faraway-binary” case maximum polarization (i.e., ∼0.7%) is observed at a considerably later time than the peak of the SN. The magnitude of polarization is dependent on the degree of unevenness in the luminosity distribution and the angle between the line of sight and the equatorial direction. When considering the geometric distortion of SN ejecta at the same time, the magnitude of polarization may either increase (for a oblate ellipsoidal shape) or decrease (for a prolate ellipsoidal shape). The polarization signatures represent a promising auxiliary instrument to facilitate the identification of the companion-fed SNe. Moreover, comparing the event rate of these special SNe with the event rate density of LIGO-Virgo-detected BH–NS/BH systems could further help to distinguish the BH–NS/BH formation channel.