Flux Concentration Effect Research Articles

Design Principle Considering Structural Mutual Effects of Double-Stator V-Shape-PM Vernier Machines for Electric Ship Propulsion

This paper proposes the design principle considering structural mutual effects of double-stator V-shape permanent-magnet (DS-V-PM) vernier machines for electric ship propulsion (ESP). Due to the flux concentration effect of the V-PM configuration, the double stators can be divided as a major and a minor stator, considering the different torque generation capability. Cooperation mutual effects between the double stators, V-PM arrangement and vernier machine topology are specifically included in the machine design principle exploration. To illustrate the design principle, first, a unified design principle is deduced, fit for general PM vernier machines. Then, a multi-step optimization strategy with auxiliary of sizing equations is presented, focusing on the parameter cooperation with flux modulation effect. Furthermore, through electromagnetic performance comparison, specific mutual effects of the DS configuration, DS angle shift, V-PMs and barrier structure are clearly summarized. Based on the DS machine design, the multi-mode operation for ESP system is introduced and analyzed. The normal/faulty cruise mode and charging mode are included to realize bi-directional operation. Prototype experiments are carried out for verification of the proposed machine design and operating strategy.

Study on Phase Change Flow and Heat Transfer Characteristics of Microalgae Slurry in the Absorber Tube of a Parabolic trough Solar Collector

The study of gas–liquid two-phase flow and heat transfer in non-Newtonian fluids is of great significance for the research and development of refrigeration and energy storage. In this paper, the characteristics and influencing factors of the phase change reaction in microalgae slurry were studied by numerical simulation and experimental verification. In order to further study the rheological and heat transfer characteristics of gas–liquid two-phase flow in the collector, the effects of wall heat flux, inlet velocity and microalgae slurry concentration on the phase change reaction in microalgae slurry were studied. The results show that when the boundary conditions of microalgae slurry with the same concentration change, the phase transition of microalgae slurry is different. The higher the wall heat flux, the more forward the phase transition occurs, and the smaller the flow rate, the more forward the phase transition occurs. When the boundary conditions remain unchanged, the phase transition point of microalgae slurry with different concentrations is the same, and the concentration of microalgae slurry will not be affected. However, the deviation between the fluid temperature and the thermal conductivity of high-concentration fluid after phase change is larger than that of low-concentration fluids. The deviation in the fluid temperature reaches approximately 10 K, and the deviation in thermal conductivity reaches approximately 0.025 W/(m·K). Therefore, the change in the fluid temperature and heat transfer intensity after phase change in microalgae slurry is more intense than that of Newtonian fluids.

Enhanced near-field radiation of acoustic-actuated antennas using embedded magnetoelectric composites

Acoustic-actuated antennas operate at the acoustic wave resonance rather than electromagnetic (EM) wave resonance and thus show a significant superiority for the miniaturization of antennas. This paper designs a new acoustic-actuated antenna using embedded magnetoelectric (ME) composites, to improve the radiations of ME antennas through the enhanced strain transfer at the interfaces between different phases. The performance of the ME antenna is examined through a multiphysics finite element method with considering the nonlinear magnetostrictive model. Then, three optimum schemes are proposed for the improvement of the ME antenna, which are also verified by the simulation results. It has been demonstrated that the EM radiations of the embedded ME composite are effectively improved by changing its sizes or configuration. Due to the magnetic flux and stress concentration effects, the maximum |E| and |H| radiations are respectively enhanced by 88 % and 97 % via using a trapezoidal magnetostrictive layer. The effects of magnetic bias and pre-stress indicate that near-field radiations of the ME antennas with fixed dimensions can be enhanced by external multi-physics fields. This simulation may facilitate the understanding of nonlinear CME behavior as well as provide a basis for the design of tunable ME antennas.

Hybrid-Magnet Variable Flux Memory Machine With Improved Field Regulation Capability for Electric Vehicle Applications

This article aims to investigate a novel hybrid-magnet variable flux memory machine (VFMM) with improved field regulation capability for electric vehicle applications. Two sets of permanent magnets (PMs), i.e., high-energy-density neodymium–iron–boron PM and low coercive force (LCF) PM, are arranged in a delta array to improve field regulation capability and torque density. The machine topology, key features, and operating principle of the presented machine are demonstrated. Based on the simplified magnetic circuit model, the underlying design tradeoffs of the presented machine are revealed qualitatively. The nonlinear magnetic circuit model of the presented machine taking saturation and hybrid-magnet leakage flux into consideration is built for machine analysis. Electromagnetic performance comparisons are carried out by finite element analysis between the presented VFMM and the existing VFMM. The results show that the presented machine can achieve significantly improved flux regulation capability while maintaining the high output torque due to the improved arrangement of hybrid magnetic branches and enhanced flux concentration effect. Finally, the investigated VFMM is prototyped. The operating principle and predicted results are verified by experimental results.

Design and Multiobjective Optimization of a New Flux-Concentrating Rotor Combining Halbach PM Array and Spoke-Type IPM Machine

In this article, a new spoke-type interior permanent magnet (PM) with a flux-concentrating rotor is proposed. Based on the flux-concentrating principle, the fitting parameters between PMs and magnetic cores on the rotor make a significant impact on the flux concentration and saliency effect, thus resulting in the output torque and power capacity. Therefore, taking the average torque, cogging torque, peak power, and PM utilization as the optimization objectives, first, the sensitivity analysis is carried out that includes the different geometric variables of the rotor. Afterward, the response surface model based on the Box–Behnken method is established by selecting the reasonable optimization variables. Then, the optimal solution of the design parameters is verified by solving the response surface model. Meanwhile, a set of Pareto solutions is generated by adopting a multiobjective genetic algorithm. By two-dimensional finite-element analysis, the electromagnetic performance of a 72-slot/16-pole topology with the optimized flux-concentrating rotor is analyzed and compared with that of the initial design model. The results are demonstrated based on the response surface model. The effectiveness of the multiobjective optimization design method and multiobjective genetic algorithm is confirmed for the flux-concentrating rotor. Finally, a 30-kW prototype is developed and experimented with to verify the finite-element analysis results as well as the effectiveness of multiobjective optimization.

Structural characterization and regression rate of solidified ethanol fuels for hybrid rocket applications

The success of hybrid rockets in future military and commercial applications will depend on their ability to utilize fuels that are not only easy-to-process, safe, and environmental-friendly but also meet operational demands of high regression rate and efficient combustion. In this study, the eco-friendly ethanol fuel is solidified using Methylcellulose (MC) and Hydroxypropyl Methylcellulose (HPMC) as the organic gellants and de-ionized water as the solvent and proposed for usage as a fuel for hybrid rocket applications. The gellant concentration is varied in the range of 10 – 14 % while the nano aluminum concentration is varied in the range 2–6 wt% for HPMC and 2–4 wt% for MC samples. Through FTIR, TMDSC, and TGA the solidification mechanism of this tri-component system is proposed. It is found that two types of non-covalent interactions lead to 3D-network formation between gellant molecules and ethanol–water mixture, and hence, solidification. One, the hydrophobic association between alkyl chains of the gellant, and two, the intra and the inter-molecular hydrogen bonding of hydroxyl groups in gellant molecules. Subsequently, the regression rate of solid fuels is investigated as a function of the oxidizer flux ranging from 0.97 – 11.7 kg/m2-s in an opposed flow burner facility (OFB). Over the range of oxidizer fluxes, the regression rate of solid ethanol fuels is higher than the conventional fuels such as HTPB and DCPD and comparable to that of paraffin wax. The high regression rate is attributed to their low melting points and enthalpy of melting, strongly shear thinning behavior, and the occurrence of vapor jetting, which in addition to fuel gasification aids in advective transport of unreacted fuel vapors to the flame zone. Finally, the effect of oxidizer flux and nanoparticle concentration on the regression rate is analyzed. Irrespective of the fuel, the regression rate increases monotonically with the oxidizer flux whose degree depends on the flow regime i.e., laminar versus turbulent; being higher for the latter. Further, in the laminar regime, there is no effect of increasing nanoparticle loading on the regression rate while in the turbulent flow regime the regression rate increases rapidly with increasing concentration.

Novel Flux-Switching Machine With Star-Array Permanent-Magnet Arrangement

This article presents a novel flux-switching (FS) machine adopting star-array permanent-magnets (PMs), termed as star-FSPM machine. In comparison with the conventional spoke-FSPM machine, the proposed one can achieve not only enhanced flux-concentration effect, but also enlarged stator-slot area, thus improving PM utilization ratio and torque density. The harmonic characteristics of both PM field and armature reaction field in the star-FSPM machine are investigated based on the field modulation theory. More importantly, the torque generation mechanism of the star-FSPM machine is also investigated and compared with that of the spoke-FSPM machine. The results show that the proposed machine can utilize the working harmonics more effectively for torque generation. Afterwards, the electromagnetic performance comparison of four PM machines is carried out by finite-element analysis. It is found that the proposed star-FSPM machine exhibits improved PM utilization ratio and enhanced torque density as compared to the spoke-FSPM machine. Finally, the theoretical analysis and FEA results are verified by experimental measurement.

Enhanced extremely weak-field energy harvesting via magnetic flux and stress concentration effects in ferromagnetic/ferroelectric composite

In this work, we report an enhanced magneto-mechano-electric (MME) coupling in Ni/Pb(Zr,Ti)O3 (PZT) ceramic composited ladder-type cantilever attached with a tip mass of NdFeB magnet, which simultaneously exhibits the magnetic flux concentration effect and the stress concentration effect, and therefore, it shows an enhanced extremely weak-field (EWF) coupling ability. Investigations show that the proposed MME energy harvester (EH) can generate an output power density of 7.16 μW Hz−1 Oe−2 cm−3, which is the highest value compared to the state of the art MME energy harvesters. Under an EWF of even as low as Hac = 0.1 Oe (about half level of the geomagnetic field), the proposed MME-EH can still produce a peak–peak output power of 23.5 μW, which is enough power to light up 4 LEDs in real time. Furthermore, it can drive a wireless sensor communication system in real time under a weak Hac = 0.75 Oe excitation, demonstrating it has potential to serve as a micro-energy source of wireless sensor networks in EWF circumstance. This work is not only beneficial but has also inspired future multi-function-integrated material and smart electronic device designs in Internet of Things in EWF circumstance.

Numerical simulation of hydrogen isotope bubbles evolution and their effect on fuel retention in tungsten

• A high nucleation rate and self-clustering of hydrogen isotope (HI) in the near-surface layer. • The appearance of the densest and largest bubbles in the near-surface layer enhances the hydrogen isotope retention significantly. • The behavior of the bubbles is strongly dependent on the operation regime in a tokamak. The 2D Hydrogen Isotope Inventory Process code with Monte Carlo bubble growth model (HIIPC2D-MC) has been upgraded by adding surface retention and self-clustering bubble nucleation to study the evolution of hydrogen isotope (HI) bubble and its impact on fuel retention. In this code, fuel retention is simulated by HIIPC2D, while the nucleation and growth of the bubble is modeled by 3D Monte Carlo code. Firstly, the dynamic behavior and mechanism of bubble nucleation is studied via self-clustering nucleation module. The effects of irradiation flux, material temperature ( T ) and trap concentration on bubble nucleation are systematically studied. The results show that the low T promotes the self-clustering bubble nucleation, large irradiation flux and low trap density lead to high nucleation rate. The long irradiation time facilitates the formation of bubbles via hydrogen self-clustering. Then, the time evolution of nucleation and growth of the bubbles is demonstrated. After the nucleation, both cascade-coalescence and pressure drive the bubbles to grow. The most and largest bubbles appear in the near-surface layer, and the HI inside the bubble plays important role on the total fuel retention. The simulation indicates the behaviors of the bubbles depend strongly on the operation regime in a tokamak. However, the bubble burst (blistering burst in experiment) is not included in the model, which will affect the bubble performance during long term irradiation.

Thermohydraulic performance of Al2O3-water nanofluid during single-phase flow and two-phase subcooled flow boiling

This study presents the thermohydraulic performance of Al2O3-water nanofluid in single-phase and two-phase subcooled flow boiling in a horizontal copper tube. The results of a three-dimensional Eulerian-Eulerian CFD model are validated with the experimental data. Having the model validated, a comprehensive parametric analysis is conducted on the effect of Reynolds number, heat flux, and volume concentration of nanoparticles on the hydrothermal performance of the heat exchanging tube. The HTC in the flow boiling regime is increased by ∼73% compared to the single phase. The heat transfer and pressure drop increased through the addition of nanoparticles to the base fluid in single-phase and two-phase flows. However, its effect is more pronounced in case of single-phase flow. Increasing the heat flux on the tube wall is associated with a slight increase in the heat transfer coefficient (HTC) and a significant decrease in the pressure drop. The HTC and pressure drop increase by moving to higher Reynolds number. The vapor volume fraction of nanofluid was lower than pure water due to a higher heat transfer and lower wall temperature. The maximum PEC (performance evaluation criterion) of 1.25 and 1.19 is found in case of single- and two-phase flows.

Significant improving magnetoelectric sensors performance based on optimized magnetoelectric composites via heat treatment

Laminated magnetoelectric (ME) composites consisting of magnetostrictive and piezoelectric materials have been investigated and proved to realize strong ME coupling, which shows great benefits to fabricate high sensitivity ME magnetic sensors. In this work, optimized L–T mode ME composites consisting of heat-treated Metglas ribbons and [110]-oriented Mn-doped 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (Mn-doped PMN-PT) single crystal fibers were reported, which achieves giant ME coupling and ultrahigh ME electric field coefficient of 4.26 × 104 V cm−1 Oe−1 at the electromechanical resonance. The equivalent magnetic noise of the ME sensor based on the proposed ME composites is only 2.89 fT Hz−1/2 at the electromechanical resonance, which exhibits great prospect in the application of precision magnetic field detection. Based on the characterization of heat-treated Metglas samples and the finite element simulation of the ME composites, the improved performance of the ME composites and ME sensors can be attributed to the enhanced properties of heat-treated Metglas (higher piezomagnetic coefficient d 33,m, higher induced magnetic flux density and lower mechanical loss) due to the enhancement of nanocrystallization and the stronger magnetic flux concentration effect corresponding to the dimension of the Metglas ribbons.

Modelling precipitate amorphization in Zircaloys

The second phase particles (SPPs) that occur in Zircaloys can undergo amorphization and loss of iron in-reactor, which can have a profound effect on corrosion resistance and irradiation growth. In this paper, a classical model is presented that predicts the interaction between these processes, based on a previously proposed physical mechanism that considers iron release and transport from the SPP as the controlling factor. It is assumed that iron is released into a mobile state by a homogeneous and continuous amorphization and recrystallization process. As iron is released, it diffuses out of the SPP, causing the relative stability of the amorphous phase to increase, until a persistent amorphous layer forms. The model predicts the growth rate of this layer and the rate at which iron is lost from the SPP. It has been used to explore the effect of flux, temperature, and initial SPP iron concentration on the amorphous layer growth and iron loss kinetics. It is predicted that whilst iron loss is correlated with the thickness of the amorphous layer, the relationship is not a simple scaling, and depends on conditions. The model is also able to explain the observed occurrence of an amorphous layer only in an intermediate temperature range as a natural consequence of the competition between the same fundamental mechanisms.

Enhancement of magnetic detection by ensemble NV color center based on magnetic flux concentration effect

The high-sensitivity magnetic sensor is the key to the weak magnetic and extremely weak magnetic detection imaging. In this paper, based on ensemble nitrogen-vacancy (NV) color center in diamond, a wide-field magnetic field distribution imaging system combined with the magnetic flux concentrator (MFC) is built for enhancing the magnetic detection. The paired T-shape chip MFC structures are designed and prepared based on the simulation of magnetic flux concentration effect, and the enhancement of magnetic field of MFC is verified by continuous wave optical detection magnetic resonance (CW-ODMR) imaging technology. When the gap width between the MFCs is 1.0 mm, the magnetic enhancement factor is about 10.35. To verify the effectiveness of the magnetic enhancement effect of the MFC, The magnetic enhancement effects are also measured under different magnetic field strengths and different gap widths. The magnetic sensitivity of the system increases from 1.10 nT/Hz<sup>1/2</sup> to 0.30 nT/Hz<sup>1/2</sup>. By comparing the simulations with the measurements, the relationship between the measured magnetic enhancement multiple and the gap width can be obtained, and the better magnetic enhancement capability and sensitivity of the experimental system are also estimated. When the MFC’s gap width is 0.5 mm, the corresponding magnetic enhancement factor is increased to 18.21, and the corresponding magnetic sensitivity is 0.25 nT/Hz<sup>1/2</sup>. These results show that the magnetic detection sensitivity of the ensemble NV in diamond can be effectively improved based on magnetic flux concentration effect, which provides a reference for the applications of precision quantum measurement technology in weak magnetic and extremely weak magnetic detection.

Axial magnetic flux amplification in Hall-magnetohydrodynamic simulations of externally magnetized z-pinches

It is shown that externally magnetized gas-puff z-pinches under compression can exhibit robust axial flux amplification under suitable axial boundary conditions. This effect relies upon the Hall term in the generalized Ohm's law to generate azimuthal currents in the presence of a driving axial electric field. Under dynamic compression, the total current tends to flow in a mostly force-free boundary layer, separating the predominately azimuthal field outside the layer and the predominately axial field inside the layer. The effect only appears to occur if the axial boundaries allow for outflow or absorption of electromagnetic energy. The effect is mitigated by imposing either periodic or conducting axial boundary conditions. A semi-analytic equilibrium analysis agrees with steady-state solutions of the time-dependent electron-magnetohydrodynamic equations and provides an estimate of the scaling of the boundary layer as well as suggesting a scenario for the formation of the boundary layer. When operative, the effect can significantly impede plasma compression due to the increase in axial flux that diffuses into the pre-compressed plasma or through the presence of conductors that inhibit movement of the generated axial flux. Several facilities have noted unusual implosion behavior in z-pinch experiments with applied axial fields that does not appear to be explainable within the standard magnetohydrodynamic model. It is suggested that these experiments can be explained by the axial flux amplification and concentration effect.

Nonlinear modeling of bending-mode magnetoelectric coupling in asymmetric composite structures with magnetization-graded ferromagnetic materials

The bending-mode magnetoelectric (ME) coupling in the asymmetric laminate composite with a magnetization-graded ferromagnetic material has been investigated in this paper. Based on the nonlinear constitutive relationships of the magnetostrictive material, the dynamic piezomagnetic models have been presented for magnetostrictive materials after considering the remanence, demagnetization, and flux concentration effects. In addition, the bending-mode resonant ME coupling model is developed based on the proposed dynamic piezomagnetic model, the motion equation of the ME composite, and the ME equivalent circuit method. The composite structures FeCuNbSiB/Ni/PZT with negative magnetostrictive Ni and FeCuNbSiB/FeNi/PZT with positive magnetostrictive FeNi have been used to confirm the validity and reliability of the theoretical model. The theoretical results show that the bending-resonant ME coefficients reasonably agree with the experimental results. This theoretical model is of importance for understanding the bending-mode ME response of the asymmetric structure with magnetization-graded ferromagnetic materials and designing the ME devices.

Characterization of mass transfer in a shallow fluidized bed for adsorption processes: Modeling and supporting experiments

This study characterizes mass transfer processes in a multi-stage fluidized bed (MSFB) using shallow fluidized beds. Multi-stage fluidized beds are of interest for sour gas removal using adsorption, examples are H2S/CO2 removal from natural gas and CO2 capture by amine sorbents. A phenomenological model based on the classical two-phase fluidization model is used to study the mass transfer process. Independent measurements and literature data are used to describe mixing, hold-ups, intraparticle mass transfer and adsorption kinetics. The bubble hold-up was experimentally measured. Mixing was investigated with a temperature response measurement. The mixing in the emulsion gas phase varies between plug flow and ideal mixing with increasing superficial gas velocity, while the solid phase is always ideally mixed. The presented fluidized bed model is able to describe the effects of superficial gas velocity, solid flux, bed height and inlet concentration. Mass transfer was further studied using a sensitivity analysis, which showed that the used shallow fluidized bed is already fairly optimized with respect to mass transfer. Shallow fluidized beds benefit from fast gas interchange because bubbles do not have the chance to grow. Optimal mass transfer and gas interchange conditions can be achieved in shallow fluidized beds for application in MSFBs.

Design of a bifunctional thermal device exhibiting heat flux concentration and scattering amplification effects

By performing a two-step coordinate transformation, an N-sided polygonal bifunctional thermal device with nonsingular homogeneous material parameters is proposed based on transformation thermodynamics. The presented device could function as not only a concentrator with heat flux concentration effect, but also an illusion device with a scattering amplification effect. Moreover, to further eliminate the anisotropy of thermal conductivity tensors, multilayer realization of the device through isotropic materials is also investigated. The effectiveness of the design method and the performance of the devices are validated by the full-wave simulations. This work paves a new way for the design of easy-to-implement bifunctional devices and has broad application prospects in such fields as thermal-energy harvesting and thermal camouflage.

Design and Analysis of Halbach Ironless Flywheel BLDC Motor/Generators

Halbach array-based permanent magnet (PM) brushless machines exhibit attractive features when compared with conventional PM brushless machines with normal segmented magnets, including the flux-concentration effect, essentially sinusoidal air-gap flux density due to PMs, and negligible cogging torque. However, as for a motor/generator used in flywheel, an external rotor composed of Halbach array and rotor back-iron is necessary to increase the inertia of flywheel system, which is different from the conventional external-rotor machines. In this paper, a Halbach array PM motor is studied compared with the radial magnet array. The relationship between the air-gap field distribution and the magnet array is discussed. Finally, the eddy current loss in PMs of the external-rotor ironless brushless dc motor is analyzed between the Halbach PM motor and the conventional PM motor.

Investigation of the magnetic properties of Si-gradient steel sheet by comparison with 6.5%Si steel sheet

In this study, we investigated the magnetic properties of Si-gradient steel sheet produced by CVD (chemical vapor deposition) siliconizing process, comparing with 6.5% Si steel sheet. The Si-gradient steel sheet having silicon concentration gradient in the thickness direction, has larger hysteresis loss and smaller eddy current loss than the 6.5% Si steel sheet. In such a loss configuration, the iron loss of the Si-gradient steel sheet becomes lower than that of the 6.5% Si steel sheet at high frequencies. The experiment suggests that tensile stress is formed at the surface layer and compressive stress is formed at the inner layer in the Si gradient steel sheet. The magnetic anisotropy is induced by the internal stress and it is considered to affect the magnetization behavior of the Si-gradient steel sheet. The small eddy current loss of Si-gradient steel sheet can be explained as an effect of magnetic flux concentration on the surface layer.

Enhanced magnetoelectric effect in Metglas/K0.5 Na0.5NbO3/metglas lead-free ME laminates

We report the magnetoelectric (ME) coupling in lead-free ME composites composed of Metglas (2605SA1) and K[Formula: see text]Na[Formula: see text]NbO3 (KNN) phases. Thickness of the magnetostrictive layers ([Formula: see text] is changed by stacking number of Metglas layers ([Formula: see text]25[Formula: see text][Formula: see text]m for each layer) while KNN is maintained at a fixed thickness ([Formula: see text]300[Formula: see text][Formula: see text]m). As the number of Metglas layers increased, the peak magnitude of [Formula: see text] first increases, reaches a maximum and then decreases afterward. The static magnetic field ([Formula: see text], where [Formula: see text] shows maximum magnitude shift toward a higher value as number of layers increases. The maximum value of [Formula: see text] 91[Formula: see text]mVcm[Formula: see text]Oe[Formula: see text] is observed for optimized thickness ratio of [Formula: see text]/[Formula: see text] 1 (i.e. [Formula: see text] 5 layers) at [Formula: see text] 160[Formula: see text]Oe. The [Formula: see text] is further enhanced by taking advantage of magnetic flux concentration effect of Metglas as a function of its sheet aspect ratio. The present composites can offer promising opportunities of engineering environmental friendly ME laminate for applications in ME devices such as energy harvester and magnetic field sensors.