Levitation Condition Research Articles

Total separation of multi-plastic wastes using magnetic levitation with adjustable sensitivity

Novel separation method with high efficiency is of great significance for mechanical recycling mixed waste plastics plays. However, the efficiency of most extant methods is restricted by their shortage that the methods can only deal with binary mixtures. In this paper, a novel magnetic levitation (MagLev) separation method based on scaled-up MagLev device is proposed to handle multi-plastics. A theoretical model on distribution of magnetic flux intensity and levitation conditions is established to guide the design of separation process. Based on the theoretical analysis, different processes for separation of multi-plastics with different purpose can be realized. The high sensitivity allows the separation of plastics with similar appearances (e.g. transparent plastics like polycarbonate and polymethyl methacrylate) and densities (difference with 0.01 g/cm3). The adjustable distribution of magnetic field changes the levitation condition of the waste plastics. Thus, the sequential separation of multi-plastics and extraction of target material from multi-plastics mixture are successfully addressed. The experiments demonstrate that the purities of separated multiple plastics reach to approx. 100 %. Furthermore, additional advantages of low cost and no energy consumed in separation process make the method a promising solution for economically-viable and environmentally-friendly mass production procedure.

Revisiting lunar dust charging and dynamics

Under the dynamic influence of near-surface plasma, intricate dynamics of lunar dust have been observed during the Surveyors and Apollo missions in the form of Lunar horizontal glow. These dynamics are primarily driven by electrostatic forces generated by the continual bombardment of solar wind and highly energetic UV photons on the lunar surface and dust particles. This paper revisits the phenomenon of dust charging within the lunar photoelectron sheath and subsequent dynamics. The investigation has been carried out using a comprehensive model of the lunar photoelectron sheath characterized by observed solar spectra, latitude-dependent Fermionic photoelectrons, non-Maxwellian solar wind electrons, and cold ions. A test dust particle is introduced into the sheath, and equilibrium charge and static levitation conditions are derived. The result of dynamical evolution suggests the existence of a narrow parametric regime corresponding to the periodic hopping trajectory of the dust particle over the lunar surface. In other cases, the dust particles are found to re-impact the surface after a single ballistic hop. We further identify that the discrete charging of the dust could be crucial in determining the dust dynamics, particularly in the tenuous plasmas. The analysis of the discrete dust charging model reveals significant discrepancies with the continuous dust charging model and suggests a lower likelihood of static dust levitation in the lunar environment. The present study is important for unraveling the fundamental processes governing surface evolution on the Moon and other airless bodies throughout the Solar System.

Liquid state property and rapid peritectic solidification of refractory Mo-33.3 at.% Zr alloy under electrostatic levitation condition

The thermophysical properties and rapid solidification mechanism of liquid Mo-33.3 at.% Zr peritectic alloy were investigated by electrostatic levitation technique, which attained a maximum undercooling of 387 K (0.16 TL). At its liquidus temperature, the density, surface tension, viscosity and solute diffusion coefficient of this refractory alloy were determined as 8.14 g/cm3, 1.60 N/m, 11.32 mPa·s and 1.41 × 10−9 m2/s, respectively. The primary (Mo) dendrite growth started from multi-point nucleation, while its growth velocity agreed well with the prediction of LKT/BCT dendrite growth theory and reached an upper value of 43 mm/s. The subsequent peritectic transition was characterized by a power-law kinetics relation between the nominal growth velocity of peritectic Mo2Zr phase and peritectic undercooling, displaying a maximum velocity of 46 mm/s. The increase of liquid undercooling facilitated the completion of peritectic transition and refined the microstructure of residual primary (Mo) phase, thus enhancing the Vickers hardness of this alloy gradually up to 1190.9 HV at the maximum undercooling.

Rapid dendritic growth kinetics of primary phase within supercooled Zr-V alloy at electrostatic levitation state

The liquid Zr100−xVx (x = 8.6, 16.5, 30) alloys were undercooled to the maximum undercooling of 364 K (0.18 TL), 405 K (0.21 TL), and 375 K (0.21 TL), respectively, by using electrostatic levitation technique. The Zr91.4V8.6 and Zr83.5V16.5 alloys present only one recalescence during liquid/solid phase transition, while the Zr70V30 alloy presents a transformation from two recalescence to one recalescence phenomenon with a critical undercooling of approximately 300 K. According to the LKT/BCT model, the calculated results of the primary β-Zr dendrite growth velocity in undercooled liquid Zr91.4V8.6 and Zr83.5V16.5 alloys agree well with the experiments. The velocity inflection points at 119 K of Zr91.4V8.6 alloy and 201 K of Zr83.5V16.5 alloy could be explained by the competition between solutal undercooling control and thermal undercooling control modes. For Zr70V30 alloy solidified in the P1 with twice recalescence, a critical second undercooling of 253 K and corresponding undercooling of 65 and 244 K are obtained. When the undercooling is in the range of 65–244 K, the second undercooling would be greater than 253 K, and the residual liquid phase would solidify into anomalous eutectic microstructure for Zr70V30 alloy. The Vickers hardness of Zr100−xVx (x = 8.6, 16.5, 30) alloys all show a quadratic relationship with undercooling. Under electrostatic levitation condition, the mechanical property of Zr-V alloys could be significantly regulated through solidifying the alloys at different undercoolings.

Direct photodegradation of internally mixed sodium chloride and malonic acid single aerosols: Impact of the photoproducts on the hygroscopic properties of the particles

Sea-salt aerosols (SSA) are one of the key natural aerosols in our atmosphere, consisting predominantly of sodium chloride (NaCl). Throughout their atmospheric transport, these aerosols undergo complex internal mixing, giving rise to a rich variety of inorganic and organic species, including dicarboxylic acids. This study investigates firstly the composition and deliquescence properties of coarse particles containing pure malonic acid (MA2, CH2(COOH)2) and internally mixed NaCl and MA2, by means of an acoustic levitation system coupled with a Raman microspectrometer. Secondly, we report here the first experimental observation and characterization of the products arising from photochemical reactions under UV–Visible irradiation (338 ≤ λ ≤ 414 nm) in the absence of an oxidant under acoustic levitation conditions in MA2 and NaCl/MA2 aerosols. Furthermore, the impact of photodegradation on the hygroscopic properties of these particles is examined. We confirmed the irreversible formation of monosodium malonate (NaMA, HOOCCH2COONa), which coexists with NaCl or MA2 on non-irradiated particles. We also demonstrated the formation of oxalic acid (OA2, HOOC–COOH) within irradiated MA2 droplets and the appearance of glyoxylic acid (GlyA, HCOCOOH) in NaCl containing droplets. The photolysis process exerts a marked effect on the hygroscopic properties of the particles, resulting in a shift in deliquescence transitions toward higher relative humidity (RH) values. This study contributes to the understanding of the intricate physicochemical processes involved in SSA during their atmospheric transport. Likewise, this work sheds light on the impacts of these types of aerosols on cloud formation and climate change.

Liquid state properties and rapid solidification mechanism of Fe-Nd-B alloy investigated under space simulation conditions

The thermophysical properties of liquid Fe84Nd10B6 alloy from superheated to undercooled state were investigated by space simulation technology combined with ab initio molecular dynamics (AIMD) simulations. The liquid density at liquidus temperature and its temperature coefficient were determined as 7.17 g·cm−3 and 5.51 × 10−4 g·cm−3·K−1, while its liquid thermal expansion coefficient was measured as 7.69 × 10−5 K−1. The ratio of specific heat to emissivity decayed as a quadratic power function. Under electrostatic levitation (ESL) condition, even though the cooling rate of liquid alloy was only 23.6–35.3 K/s, a maximum 131 K undercooling was realized. As alloy undercooling rose, the grain size of primary α(Fe) dendrite was refined, whose volume fraction decreased from 26.2% to 22.0%. Meanwhile, the volume fraction of major peritectic τ1(Nd2Fe14B) phase was increased from 68.6% to 76.8%, which was accompanied by the reduction of peri-eutectoid τ2(Nd1.1Fe4B4) phase down to 1.2%. In the case of microgravity processing by drop tube, liquid undercooling and cooling rate respectively reached up to 260 K (0.16 TL) and 3.9 × 104 K/s for the falling alloy droplets. Instead of τ1 phase, the primary α(Fe) phase occupied the largest volume fraction of 49.7% in large alloy droplets. At enhanced undercooling and cooling rate, the peritectic τ1 phase only increased from 26.2% up to 43.5%, whereas those of α(Fe) and τ2 phases declined to 44.0% and 12.5%, respectively. It was found that the increase of liquid alloy undercooling promoted the peritectic transformation to some extent, but high cooling rate greatly restricted peritectic reaction by reducing reaction time. The coupled effect of liquid undercooling and cooling rate controlled the volume fraction of each phase in rapidly solidified microstructures.

Study on helium gas bubble levitation in high field superconducting magnet

The abnormal temperature rise and early quench often happened to the high field superconducting magnet, especially when the magnetic field is higher than 20 T. This phenomenon is attributed to helium gas bubbles levitation in the special high magnetic field environment. So, it is very important to accurately identify the formation and distribution of helium gas bubbles levitation for the development of high field superconducting magnet. In this paper, a new analytical method based on pressure is proposed to analysis the formation conditions and the spatial distribution of helium gas bubbles levitation. And a no-insulation REBCO insert coil was also developed to study the phenomenon of helium gas bubbles levitation. The REBCO insert coil was tested in high magnetic field produced by a water-cooled magnet. The new analytical method was used to simulate the formation conditions of helium gas bubbles levitation and the temperature distribution of the REBCO insert.

Heat transfer, vapour diffusion and Stefan flow around levitating droplets near a heated liquid surface

We consider a slowly condensing droplet levitating near the surface of an evaporating layer, and develop a mathematical model to describe diffusion, heat transfer and fluid flow in the system. The method of separation of variables in bipolar coordinates is used to obtain the series expansions for temperature, vapour concentration and the Stokes stream function. This framework allows us to determine temperature profiles and condensation rates at the surface of the droplet, and to calculate the upward force that allows the droplet to levitate. Somewhat counter-intuitively, condensation is found to be the strongest near the bottom of the droplet, which faces the hot liquid layer. The experimentally observed deviations from the classical law predicting the square of the radius to grow linearly in time are explained by the model. A spatially non-uniform phase change rate results in a contribution to the force not considered in previous studies, and comparable to droplet weight and the upward force calculated from the Stokes drag law. The levitation conditions are formulated accordingly, resulting in the prediction of levitation height as a function of droplet size without any fitting parameters. A simple criterion is formulated to define the parameter ranges in which levitation is possible. The results are in good agreement with the experimental data except that the model tends to slightly underpredict the levitation height.

Microstructure control and micromechanical property enhancement of CoCrFeNiZr0.5 alloy under melt quenching and electrostatic levitation conditions

Microstructure control and micromechanical property enhancement of CoCrFeNiZr0.5 alloy under melt quenching and electrostatic levitation conditions

Experimentally Created Magnetic Force in Microbiological Space and On-Earth Studies: Perspectives and Restrictions

Magnetic force and gravity are two fundamental forces affecting all living organisms, including bacteria. On Earth, experimentally created magnetic force can be used to counterbalance gravity and place living organisms in conditions of magnetic levitation. Under conditions of microgravity, magnetic force becomes the only force that moves bacteria, providing an acceleration towards areas of the lowest magnetic field and locking cells in this area. In this review, we consider basic principles and experimental systems used to create a magnetic force strong enough to balance gravity. Further, we describe how magnetic levitation is applied in on-Earth microbiological studies. Next, we consider bacterial behavior under combined conditions of microgravity and magnetic force onboard a spacecraft. At last, we discuss restrictions on applications of magnetic force in microbiological studies and the impact of these restrictions on biotechnological applications under space and on-Earth conditions.

Excitation field and parameters of traction superconducting synchronous motor of pipeline transport

Movement of passenger crews in a rarefied air tube at speeds over 600 km/h involves the effect of magnetic levitation and a traction linear superconducting synchronous motor with a stator winding distributed along the length of the tube and a superconducting excitation system on the crew. Conditions of magnetic levitation stipulate that the position of the crew in the tube is characterized by six degrees of freedom, so a traction linear superconducting synchronous motor must be considered as a multi-stage dynamic system. However, in the “normal” operational mode, the problem is reduced to consideration of the system with one degree of freedom with the coordinate that determines the position of an inductor with superconducting winding and without ferromagnetic cores relative to the running magnetic field of the stator winding. The specifics of magnetic levitation of the moving crew, which consists in the possibility of its spatial displacement, cause the appearance of geometric parameters characterizing progressive and rotational perturbations of the coordinates of the center of inertia of the crew in expressions for mutual inductances between the superconducting excitation system, electromagnetic shield, and the stator phase windings.

Substrate-free self-assembly of peptides nano-particles through acoustic levitation

Peptides self-assembled into nano-structures such as nano-tubes have shown to have great potential in different biomedical applications. However, when it comes to interacting with biological environment, the need for substrate (e.g. glass, silicone, and gold) during the self-assembling process, can have potential impeding effects, both on the resultant nanostructures as well as the very diligent biological subparts such as cells. This work, for the first time, shows the possibility of a substrate-fee peptide self-assembling process, through acoustic levitation. A pair of transducers was used to create standing acoustic waves at a high frequency of 40KHz to levitate water-based droplets. Two independent control variables of the self-assembling process were considered, namely the peptide concentration level and the velocity amplitude of the acoustic wave, to understand their effects on controlling the morphology, alignment and dimensional properties of the resultant nano-structures. The results showed that, at low concentration level of 1 mg/ml and independent of the velocity amplitude, no clear nano-structure was developed under the levitation conditions. However, at the concentration levels above 1.5 mg/ml, self-assembly of the peptide nano-particles do happen while the velocity amplitude can significantly affect the resultant nano-structures, in terms of fiber morphology, fiber dimension and fiber alignment. We also found that under levitation conditions, there is a preferred length for the resultant nano-fibers which is independent of the control variables, while the number of nano-fibers with that dominant size depends on the concentration level.

Dynamic nucleation in sub-critically undercooled melts during electromagnetic levitation

By classical nucleation theory, sub-critically undercooled melts in electromagnetic levitation are expected to be very stable for extended periods of time. While electromagnetic levitation experiments are typically consistent with classical nucleation theory, there have been several historical instances including experiments on zirconium during the MSL-1 campaign and during the IML-2 experiments where the molten sample solidified at sub-critical undercoolings. While different electromagnetic levitation conditions were present in these anomalous nucleation events, both sets of anomalous nucleation events were attributed to dynamic nucleation. The work presented here investigates more recent experiments in the International Space Station Electromagnetic Levitation facility in which both sets of anomalous nucleation events were replicated and further investigated. The conditions of the MSL-1 solidification events were replicated in the ISS-EML using a pure zirconium sample held in isothermal conditions between 45 °C and 290 °C below the melting temperature. The sample successfully solidified in 18 of these experiments in less than 600 s where classical nucleation theory predicts the melt to remain liquid for very long periods of time. The IML-2 result, was replicated in the ISS-EML in which a Zr64Ni36 sample was used to demonstrate pulse-triggered nucleation events. During these experiments, the excitation pulse triggered solidification in the sample which was held between 59.5 °C and 64.5 °C below the melting temperature. Again, classical nucleation predicts that under these conditions the sample will remain molten. The results of both sets of experiments are consistent with dynamic nucleation theory in which nucleation events are affected by the flow conditions within the drop.

Fluid flow and vortex-shaped structure formation mechanisms ofAl-Ag-Ge alloy

<p indent="0mm">Fluid flow and solidification mechanisms of Al₇₀Ag₂₀Ge₁₀ alloy were systematically investigated using electromagnetic levitation, induction, arc, and resistance melting techniques coupled with finite element simulation method. A unique type of vortex-shaped microstructure was formed in these four experiments. This was different from the result under slow solidification conditions. The formation of the vortex-shaped structure was affected by fluid flow and cooling rate of alloy melt. The Lorentz force caused turbulent flow in alloy melt, while the turbulent flow during arc melting was driven by arc force under electromagnetic levitation or induction melting conditions. The surface tension and buoyancy force caused laminar flow in alloy melt during the resistance melting process. Due to rapid flow, the Ag₂Al phase nucleated ahead of the Al phase, primarily under near-equilibrium conditions. The metastable Ag₂Al dendrites grew as vortex-shaped morphology and preserved the melt flow pattern during solidification. The increased cooling rate caused a rapid growth of metastable Ag₂Al dendrites with increased vortex density. The curvature radius of metastable Ag₂Al dendrites decreased with enhanced melt flow; meanwhile, the more drastic nucleation and growing competition among phases occurred. Finally, irregular Al, Ag₂Al, and Ge ternary eutectics fully formed inside the vortex-shaped structure.

Kinetic Aspects of Phosphorus Removal from Electromagnetically Levitated 600 MPa Steel Droplets

A kinetic model was developed to study the dephosphorization of 600 MPa steel droplets under electromagnetic levitation conditions. The relationships which were derived from the model between dephosphorization and the influence of temperature and gas flow rate were in good agreement with experimental data. Both temperature and gas flow rate were conducive to the evaporation of phosphorus, with the effect of temperature having a greater influence than that of the gas velocity. The results show that the rate-controlling step for the dephosphorization process was diffusion within the gas phase. This work aims to provide a theoretical basis for process optimization during the dephosphorization of 600 MPa steel.

Multisensory stimulation

Multisensory stimulation

Influence of Selected Model Parameters on the Electromagnetic Levitation Melting Efficiency

The article presents the results of multivariate calculations for the levitation metal melting system. The research had two main goals. The first goal of the multivariate calculations was to find the relationship between the basic electrical and geometric parameters of the selected calculation model and the maximum electromagnetic buoyancy force and the maximum power dissipated in the charge. The second goal was to find quasi-optimal conditions for levitation. The choice of the model with the highest melting efficiency is very important because electromagnetic levitation is essentially a low-efficiency process. Despite the low efficiency of this method, it is worth dealing with it because is one of the few methods that allow melting and obtaining alloys of refractory reactive metals. The research was limited to the analysis of the electromagnetic field modeled three-dimensionally. From among of 245 variants considered in the article, the most promising one was selected characterized by the highest efficiency. This variant will be a starting point for further work with the use of optimization methods.

Levitation conditions for condensing droplets over heated liquid surfaces

We report experimental studies and develop mathematical models of levitation of microscale droplets over an evaporating liquid layer. The maximum size of droplets is estimated from the balance between gravity and Stokes force due to the action of upward Stefan flow generated by evaporation. Mathematical models of diffusion around levitating droplets allow us to determine Stefan flow velocity at the liquid layer surface. These results are then used to determine the dependence of levitation height on droplet size. Experimental data for a range of conditions are shown to collapse onto a single curve predicted from the model.

Rapid Growth of TiNi intermetallic compound within undercooled Ti50Ni50 alloy under electrostatic levitation condition

The undercooling dependence of the solidification mechanism was systematically explored by the electrostatic levitation (ESL) facility. During the experiments, the maximum undercooling reached up to 406 K (0.26 TL) and the growth velocity of the primary TiNi phase was in-situ determined at various undercoolings. At the initial increase of alloy undercooling, the value of growth velocity sluggishly rose followed by a power function. In this case, the primary TiNi phase preferentially developed as the equiaxed dendrite, then the remnant liquid participated as Ti2Ni and α-Ti phases on the grain boundary. Once the undercooling exceeded the critical value of 350 K, the growth velocity of the primary phase displayed a sharply increase tendency. Meanwhile, the TEM results demonstrated that the precipitation of the intermetallic Ti2Ni compound was gradually restrained during the rapid solidification and the R-phase existing in the TiNi matrix at large undercooling implied that the martensitic transformation was incomplete.

Single Crystal Growth and Chemical Disorder Trapping of Refractory MoNbReTaW High-Entropy Alloy Solidified Under Electrostatic Levitation State

The disorder trapping induced by supercooling is innovated to promote the formation of chemically disordered solid solution phase in high-entropy alloy (HEA) when the ordered phase is more inclined to form. We design a new MoNbReTaW HEA, consisting of the top five refractory metals with the highest melting points, whose liquidus temperature attains 2788 K. It is featured with a very large negative enthalpy of mixing and a strong mismatch of atomic size. As a result of sluggish atomic diffusion under a sufficient supercooling up to 500 K and consequent disorder trapping at a crystal growth velocity of 15 to 25 m/s, the original single solid solution phase with a conspicuous local chemical ordering transforms into a chemically disordered state. Owing to the decrease of atomic size mismatch, not only the lattice is turned out to be well-aligned but also the dislocation density is reduced. By the supercooling-based rapid solidification approach under electrostatic levitation condition, we successfully achieved the growth of spherical single crystals with 2 to 3.5 mm in diameter and interior misorientation less than 2 angle degrees. The notable suppression of microsegregation helps to enhance the microhardness to 6.8 GPa at the maximum supercooling of 538 K. Disorder trapping contributes to the increase of nanohardness up to 11.2 GPa. The liquid supercooling is capable of strengthening the mechanical property by optimizing the local chemical ordering.