Papers by Keyword: Gravity

Abstract: According to Stokes, the time required for a particle to precipitate depends on several conditions such as sphericity and laminar flow, as well as key parameters like particle size, densities (particle and fluid) and fluid viscosity. Therefore, if any of these conditions or parameters are unknown or not met, it becomes impossible to estimate the precipitation time. Additionally, when the separation under 1-g (Earth gravity) takes days or months but an estimation is needed in just minutes, the separation time at 1-g can be approximated by relating it to conditions at other values of gravity (n-g). For example, in a centrifuge. However, this n-g value is not reached instantaneously but require to consider the acceleration, plateau, and deacceleration phases to obtain a reliable estimation. This task has been addressed before; however, the resulting models tend to be either complex for practical laboratory use, or fail to account for the relationship between distance travelled by a particle under 1-g and the distance travelled under centrifugal forces. Moreover, even during the plateau phase, centripetal acceleration is unsteady because the radial distance of the precipitating particle is constantly changing. Thus, the aim of this study is to simplify the methodology for estimating particle separation time at 1-g by using separation time obtained under the unsteady conditions of centrifugation, even when the properties of the particle and fluid are unknown, through a numerical approach.

Abstract: The article considers the use of numerical methods in the SCILAB environment for modeling particle trajectories under the influence of various physical forces: gravity, electromagnetism and friction. The simulations conducted allowed us to study the dynamics of particle motion in three-dimensional space under various conditions, in particular the influence of forces on changing trajectories and stabilizing motion. The results obtained demonstrate the effectiveness of using the SCILAB software as a tool for numerical modeling of complex physical systems, which ensures the accuracy of calculations and clarity of visualization. It should also be noted that the use of such approaches allows us to study particle motion in various fields of science and technology, in particular in physics, engineering and systems analysis. Numerical methods implemented in SCILAB provide flexibility in taking into account the initial conditions and parameters of the system, opening up prospects for further research into complex interactions in multicomponent systems.

Abstract: The article discusses the application of the discrete element method (DEM) for modeling the behavior of spherical particles in granular media. Key aspects of particle contact interactions, including frictional forces, elasticity, coordination number, and the shape factor of spherical particles, are analyzed and investigated. It is worth noting that the proposed methodology enables the study of the mechanical properties of systems with particles of various sizes and compositions, as well as the modeling of their behavior in confined spaces and under dynamic influences. The modeling results demonstrate the high accuracy and versatility of the DEM for analyzing processes in bulk materials, particularly transportation, mixing, and granulation. The findings underscore the effectiveness of using DEM to solve complex problems and highlight prospects for its further improvement.

Abstract: By replacing the interface with sharp change properties with a functionally graded material with a gradually changing composition, a stable interface can be formed for mechanical and functional properties. In this study, the final goal is to functionally grade the interface between aluminum and alumina (Al₂O₃)/aluminum (Al) composites. First, the segmentation velocity of Al₂O₃ particles under gravity was measured to clarify the possibility of functional grading. The starting materials used were A356.0 Al alloy and α-type Al₂O₃ particles. The segmentation velocity obtained by the experiment was much faster than the theoretical velocity obtained by Stokes' law. It seems Stokes' law assumes that the particles are spherical and there is no interaction between particles, but the actual particle velocity was affected by the actual particle shape and interaction between particles. These factors affect the change in the segmentation velocity. The height of the mold was set to 40 mm, and an Al₂O₃ particle/Al composite with a particle size of 6.7 μm was placed on the top and an Al alloy was placed on the bottom in the mold, melted, and rapidly solidified after 12 sec., and an Al₂O₃ particle-dispersed Al alloy functionally graded composite was obtained under gravity.

Abstract: Compared with traditional shielded metal arc welding and semi-automatic welding, fully automatic welding has the advantages of fast welding speed, high welding quality as well as a high qualification rate on the premise of ensuring the comprehensive performance of the girth weld joint. Meanwhile, the proportion of welding defects also changed from porosity and slag inclusion to lack of fusion. Therefore, from the view of the macroscopic and dynamic evolution behavior, the paper aims to reveal the influence of the coupling of weld-pass morphology and molten-pool flow on the formation of lack of fusion using macroscopic metallographic observation and high-speed photography. The results indicate that the weld morphology is prone to convex reinforcement and larger penetration depth in the 6 o’clock direction of the pipeline girth weld under the reference parameters. The excessive reinforcement of the pass to be welded is one of the sufficient conditions for the formation of a lack of side fusion in the 6 o’clock direction. Excessive reinforcement could lead to welding arc heat mainly used to melt the raised weld metal to be welded, which results in insufficient heat flow to both sides of the molten pool metal. Furthermore, due to the larger curvature radius at the groove and the increase of the surface tension of the molten pool with lower relative temperature, the flow resistance of the molten pool increases and the fluidity decreases.

Abstract: As it is well established, Stokes law has been used to calculate the time required to precipitate a particle in a fluid under specific conditions such as sphericity, laminar flow, differences on densities (particle and fluid) and fluid viscosity for a specific gravity force (g). However, when the separation under 1-g takes days or months and it is crucial to estimate that time in just minutes, the separation time at 1-g can be estimated making a relationship with any other g (n). However, in any centrifuge the n value is not reached instantaneously but in a specific time and during this time the g-value is never constant, but it is always growing (at the first stage). Then, after reaching the n-value, the centrifuge could stay at that value for a certain time and then, (the third stage) the n value will change again, this time decreasing. Therefore, the aim of this study is to establish a mathematical model that considers the acceleration and deceleration periods and expresses them as equivalents of the n period by using a numerical approach [1-3]. It is expected the g-equivalent concept increases the certainty of the separation time estimation.

Abstract: This work presents studies on the material composition and physico-mechanical characteristics of an alumina-containing estimate formed during the production of aluminum on electrolyzers with self-baking anodes during technological operations. The material is a mixture of fine powder 2.5 mm in size (62.78% on average mass) with the presence of pieces of material ranging in size from 0.5 to 6 cm (average 20.26% by weight). The samples contain pieces of hardened aluminum with sizes from 5 to 20 mm (16.96%). The largest content in the sample has the fineness classes-0.315 + 0.16 mm in the volume of 29.85% and the largest class +2.5 mm-37.22%. B It was established that aluminum is concentrated in the fractions-0.315 + 0.16 mm (45.7%) and 0.16 + 0 mm (48.8%), silicon in the fraction-0.63 + 0.315 mm (1.91%), iron at-1.25 + 0.63 mm (0.601%) and-0.63 + 0.315 mm (0.62%). The material consists of cryolite (Na₃AlF₆), chiolite (Al₃F₁₄Na₅), quartz, feldspar, carbonaceous matter and the technogenic phase of the composition (NaF) 1.5CaF₂ AlF₃. The material is characterized as non-abrasive (working index Ai - 0.0184) and very soft in relation to impact crushing (working index CWi - 3.64), the working index of ball grinding Bond (BWi - 6.47) characterizes a very low resistance to ball grinding. The implementation of the crushing operation of an alumina-containing estimate will allow the use of dry cascade-gravity and centrifugal classification to separate impurities in the form of SiO_2, and Fe₂O₃ for the use of alumina-containing material in primary aluminum technology. On the basis of laboratory tests, it is established that alumina-containing raw materials can be separated and photometric and gravitational separation methods can be used. A mathematical model of the motion of particles of primary and prepared alumina-containing raw materials in a cascade-gravity classifier was developed. The criteria and factors characterizing the alumina-containing material, as well as influencing and determining the maximum material enrichment, are established.

Abstract: The solidification experiments about macrosegregation formation of the Al-10%Bi hyper monotectic alloys under gravity conditions have been carried out. The results showed that the average diameter of the Bi-rich droplets linearly increases and the number density of the Bi-rich droplets exponentially decreases with solidification time under the gravity condition. Because of gravity settling and collisions coagulation between the droplets, area fraction of Bi-rich increased rapidly in the bottom of samples during early solidification. It’s easy to form Bi-rich layer at the bottom of the sample. The analysis demonstrates that nucleation and diffusion growth of drops are the dominant factors influencing the solidification microstructure during the early solidification and the same distribution of Bi-rich in different locations of sample. As the solidification process, gravity migration and collision coagulation beginning to play the leading role, lead to the difference in the distribution of Bi-rich droplets in different locations of sample 90%e5%a2%9e%e5%a4%a7&tjType=sentence&style=&t=increases+gradually" increases gradually in the same time. It caused macrosegregation of the final solidification microstructure under the gravity condition.

Abstract: Sintering involves several interactions as particles bond and enable microstructure evolution toward a minimized energy condition, resulting in a complex interplay of measurement parameters. Overriding the evolution is energy minimization, and from that perspective some simple relations emerge. The natural progression is determined by energy reduction, measured by surface area, density, and grain boundary area (grain size). Contrary to the usual sintering analysis that starts with atomic level mass transport mechanisms, presented here is an approach that links to global energy reduction during sintering to simple monitors. Initially sintering converts surface area into lower energy grain boundary area. Subsequently grain growth annihilates grain boundary area. Thus, grain boundary area peaks at intermediate sintered densities, while surface area continuously declines. The trajectory follows a straightforward dependence on density as illustrated using data for a wide variety of materials and consolidation conditions.

Abstract: In principle gravity will affect everything. Although practically negligible it is legitimate to inquire the effect of gravity on the electromagnetic properties of materials which can be expressed as the relation between (d,b) fields (electric displacement and magnetic induction) with the (e,h) fields (electric and magnetic field strength). A sample of material in a weak gravitational field is equivalent with placing the sample in an accelerating reference field (which is the statement of the equivalence principle). By using the relation between the accelerating frame with the inertial frame we can compute the electromagnetic properties with the assistance of CAS (Computer Algebra System) Reduce due to the tedious algebraic manipulations needed to accomplish the task. The linear and isotropic relation in inertial frame (free of gravity), although still linear, becomes unisotropic and mixed up between electric and magnetic fields.