Increase Of Field Intensity Research Articles

Reduction of the supercooling of Ca(NO3)2•4H2O using electric field and nucleating agent effects

The performance of thermal energy storage systems with Ca(NO3)2•4H2O (abbreviated as CaNT) as a phase change material is limited by its complex thermal properties and relatively large degree of supercooling. In this study, we demonstrate active and passive methods to reduce the degree of supercooling via the addition of electrical energy and nucleating agents. The degree of supercooling decreases almost linearly with an increase in the electric field intensity, whereas the crystallisation period shows the opposite trend. Twelve types of nucleating agents were chosen based on the Edisonian method, and the effectiveness of each agent was tested by adding 1 wt% of nucleating agent to CaNT. The effect of the nucleating agent is clearly observed in the variation in the freezing temperature. We found that carbonate anions and earth alkali cations were the most suitable, and the best results were obtained for the BaCO3 nucleating agent. It showed the smallest degree of supercooling and standard deviation value. The TG/DTA curves indicate that careful heat treatment is essential for the nucleation of CaNTs. Both the electric field and nucleating agent contribute to heterogeneous nucleation, and in this case, the application of an electric field leads to a flow of current and the formation of complex compounds. The analysis of the FT-IR spectra revealed different roles and the mechanisms of the electric field and nucleating agent in inducing the nucleation of CaNTs.

Relative Paleointensity Record of Integrated Ocean Drilling Program Site U1396 in the Caribbean Sea: Geomagnetic and Chronostratigraphic Observations in the Pliocene

AbstractContinuous sedimentary records of paleomagnetic directional variability and relative paleointensity (RPI) provide valuable information on the evolution of the geodynamo while also facilitating stratigraphic correlation and age control. While the Quaternary RPI record has received much attention, Pliocene records are relatively rare. Here, a u‐channel paleomagnetic study from Integrated Ocean Drilling Program (IODP) Site U1396 in the Caribbean Sea refines the shipboard‐derived polarity stratigraphy and generates an RPI and directional record extending back 4.5 Ma. Rock magnetic data reveal changes in magnetic coercivity around 2.1 Ma that influences the quality of the paleomagnetic record; while the older record is well‐resolved and passes RPI quality criteria, much of the younger section does not. To facilitate the development of the RPI record, spike noise associated with discrete intervals of volcanogenic sediments are filtered from the data set. The resulting record passes RPI reliability criteria between 0–0.6 Ma and 2.1–4.5 Ma and represents the highest resolution RPI record extending into the early Pliocene. We use this record to refine the existing benthic δ18O chronology and open the door to high‐resolution RPI chronostratigraphies during the Pliocene. Although we find no evidence for a previously observed increase in magnetic field intensity after ∼4 million years ago, we do observe an asymmetrical form to RPI in the normal polarity intervals of the Gauss chron. We also find a polarity bias in inclination that cannot be simply explained by a drill string overprint, suggesting polarity‐driven field asymmetries that are particularly pronounced during the Pliocene.

Effect of pulse magnetic field treatment on the hardness of 20Cr2Ni4A steel

This article reports that pulse magnetic treatment affects the hardness of 20Cr2Ni4A steel and combs the structure to make it more uniform. According to the experimental requirements, the pulsed magnetic processing system is designed and built, and 1 T, 4 T, 9 T pulsed magnetic processing is applied to the material. The mechanical properties of 20Cr2Ni4A steel before and after magnetic field treatment were quantitatively studied by measuring microhardness and residual stress. XRD and EBSD data are used to analyze the interstitial carbon content and the change of Fe-C comparison. Calculate the dislocation density, and further observe the dislocation structure by TEM. The magnetic domain is characterized by MFM and illustrates the effect of pulsed magnetic treatment on the magnetic domain and dislocations. The results show that the alloy steel has better mechanical properties after pulse magnetic treatment. As the magnetic field intensity increases, the average microhardness increases, and the hardness range is reduced. Different magnetic field treatments reduce the average residual stress of the material, especially after 1 T magnetic field treatment, the average residual stress is reduced by 34.4%, and residual stress distribution is more uniform. The magnetic treatment increases the solute carbon content in the gap of 20Cr2Ni4A steel by about 0.01% and the proportion of α-Fe phase increases. In addition, the magnetic field treatment reduces the dislocation density in the dislocation accumulation area, the proliferation and diffusion of dislocations increase the overall dislocation density. The magnetic domain changes from labyrinth with higher stress to lamellar with lower stress, so stress concentration is weakened and the distribution of residual stress is uniform. This study shows that pulsed magnetic treatment regulates the hardness and residual stress of 20Cr2Ni4A steel, homogenizes the structure of the material and improves the overall performance.

Research on the formation mechanism of magnetized water used to wet coal dust based on experiment and simulation investigation on its molecular structures

To better improve the effects of magnetization on the solution wettability, in this paper, the formation mechanism of magnetized water was investigated based on the combined method between the numerical simulation and experiments. The simulation results indicated that magnetization can reduce the first wave of the radial distribution function of water molecules; meanwhile, with the increase of magnetic field intensity, the diffusion coefficient of water molecules shows the four stages of changes, i.e. the slow change (0–200 mT), rapid increase (200–350 mT), stable period (350–450 mT) and reduce period (450–500 mT). In addition, the experimental results also show that as the magnetic field strength increases (0–350 mT), the K-M value of the solution gradually decreases, indicating that the hydrogen bond structures among the water molecules are reduced, which further verifies that the large molecular clusters break into smaller molecule groups under the magnetic field. The surface tension and contact angle of the magnetized water were reduced by 6.33%, 13.47% than that of the untreated water, respectively. It was concluded that the magnetization mainly destroys the hydrogen bond structures among the water molecules and reduces the solution cohesion to improve the solution wettability, which is of great significance for proposing the novel dust control technologies based on the magnetic method.

Terahertz Characteristics of Magnetic Fluid Based on Microfluidic Technology

Magnetic fluid is a new functional material with both liquid fluidity and solid magnetism, which has important application value in medicine, biology, and so on. In this study, terahertz technology and microfluidic technology were combined to investigate the terahertz transmission characteristics of a magnetic fluid in different magnetic fields and different electric fields. In the external magnetic field, the intensity of the terahertz spectrum increased with an increase in the magnetic field intensity, and the response to the magnetic field in different directions was different. Under the applied electric field, the intensity of the terahertz spectrum decreased with an increase in the electric field intensity. This method is convenient for studying the terahertz characteristics of magnetic fluid and provides technical support for in-depth studies of magnetic fluid.

Magnetic sensor based on WGM hollow microbubble resonator filled with magnetic fluid

In this work, a magnetic sensing scheme based on whispering gallery mode (WGM) hollow microbubble resonator (HMR) filled with magnetic fluid (MF) is proposed. The HMR is made by the pressure-assisted arc discharge method on the microcapillary. WGM is excited by evanescent fields in HMR. The quality factor of resonator is 4.02×106. Then, the influence of the wall thickness of HMR and the concentration of MF on the sensor is studied both theoretically and experimentally. When MF is infiltrated in the HMR, the refractive index (RI) of the MF increases with the increase of the magnetic field intensity, resulting in the shift of the resonance wavelength. By reducing the wall thickness, the magnetic sensing sensitivity is increased from 2.6 pm/mT to 25.21 pm/mT within the magnetic field intensity range of 2 mT–20 mT. In addition, the increase in the concentration of MF and the clustering phenomenon caused by it have also been observed. This work provides a novel magnetic sensing scheme, and the proposed WGM resonator has great application prospects in optofluidic sensing.

Thermorheological properties of magnetorheological grease and its thermomagnetic coupling mechanism

A heating phenomenon exists in the service process of magneto-rheological devices. For magnetorheological devices using magnetorheological grease (MRG) as the working medium, changes in the medium’s rheological behaviors caused by temperature increase will generate challenges in the reliable service of the devices. With laboratory-prepared MRG as the research object, MRG rheological property laws under different temperatures and magnetic field intensities are investigated, and the magnetic properties of carbonyl iron (CI) powder under different temperatures are analyzed. The relationship between the evolution of the MRG structural system and changes in rheological properties under the action of thermomagnetic coupling is discussed. The results show that the MRG structural system is composed of base carrier liquid soap fibers and magnetic chains under the action of a magnetic field, and the soap fibers can strengthen the structural intensity of the MRG. A decrease in the entanglement degree of the soap fiber structure caused by temperature increase will obviously weaken the intensity of the entire MRG system and narrow the regulation and control scope of the MRG rheological properties. The structural evolution of soap fibers under thermomagnetic coupling will affect the chain formation of magnetic particles and ultimately their rheological properties. At low temperature and magnetic field intensity, the entanglement degree of soap fibers is relatively high, and the magnetic force on magnetic particles is weak, which cannot completely overcome the binding of soap fibers. The influence of soap fibers is the dominant factor affecting the MRG rheological properties. As temperature and magnetic field intensity increase, the entanglement degree of soap fibers decreases, magnetic particles gradually disperse from the soap fibers under the action of a large magnetic field force, and the magnetic chain structure gradually becomes the dominant factor affecting the MRG rheological properties. Moreover, the weakening degree of the temperature increase effect on the MRG rheological properties decreases, and the rheological law changes gradually.

A novel strategy to enhance the generating power of ionic polymer metal composites through magnetoelectricity

In this paper, we put forward a method to enhance the output power of ionic polymer metal composite (IPMC) through a magnetic field by combining the ion-electronic and magnetoelectric effects. Firstly, we confirmed that the total output voltage of IPMC deformation originates from the vector superposition of ion-electronic and magnetoelectric effects when applied a magnetic field. The open circuit voltage and output power of IPMC were experimentally investigated by adjusting the deflecting frequency and magnetic field intensity. As the frequency and magnetic field intensity increase, the increased voltage and output power caused by the magnetic field show an upward trend. Then, the experimental results were analyzed and verified through the piezoelectric and magnetoelectric theory. The results show that the increased voltage has a linear relationship with the frequency and magnetic field intensity and has nothing to do with the inherent parameters of IPMC itself. Finally, we performed simulation and practical tests to verify the energy harvesting effect of this strategy. During the energy harvesting test of water flow fluctuation, the open circuit voltage was increased by 41.91% and the output energy was increased by 110.03%, which indicates that this strategy has excellent performance in practical applications. By this study, the power generation performance of IPMC was explored and improved through multiple physical mechanisms.

Experimental investigation on the dynamic behavior of small droplet in a uniform DC electric field

To study water droplet dynamic behavior in the silicone oil under a uniform DC electric field, a visual experiment system is set up. Two parallel plates are placed to form a uniform DC electric field. Results show when the electric field intensity is less than 2.33 kV/cm, with the increase of the electric field intensity, the droplet stretches in the vertical direction. The droplet detaches from the lower plate at 2.45 kV/cm. The droplet breaks into two daughter droplets at 3.67 kV/cm. Two daughter droplets coalesce at 4.67 kV/cm. A liquid bridge is formed at 4.93 kV/cm.

Impact of Magnetic Field Environment on the EDM Performance of Al-SiC Metal Matrix Composite.

In the present work, a hybrid magnetic field assisted powder mixed electrical discharge machining had been carried out on the Aluminum-Silicon Carbide (Al-SiC) metal matrix composite. The aim of the study was to obtain higher surface finish, and enhanced material removal rate. The dielectric mediums employed were plain EDM oil, SiCp mixed and graphite powder mixed EDM oil for flushing through the tube electrode. The magnetic field intensity, discharge current, T-on/off duration and type of dielectric were the control variables used for present investigation. From the results, it was observed that the machining variables for instance, discharge current, T-on/off duration and type of dielectric conditions remarkably affected the material removal rate, micro-hardness and surface roughness of the machined composite material. The MRR augmented considerably with an increase in the magnetic field intensity along with peak current. Subsequently, the composite with lesser vol.% of SiC particulates witnessed sharp rise in MRR in maximum magnetic field environment (0.66T). In addition, quality of the machined surface improved significantly in graphite powder mixed dielectric flushing condition with intermediate external magnetic field environment. Besides, an enhancement of micro-hardness was quantified as compared to base material due to the transfer of the material (SiCp) during powder mixed ED machining.

Segregation in magnetized fluidized bed with Geldart-B magnetizable and nonmagnetizable particles

For magnetized fluidized beds with Geldart-B magnetizable and nonmagnetizable particles operated under the magnetization-LAST mode, segregation occurs and deepens as the magnetic field intensity increases. This work aimed to explore the effects of particle size and density difference on such segregation. The field intensities (His and Hcs) for the segregation to initiate and complete increased as the gas velocity (Ug) increased. Moreover, their increases were steeper at higher gas velocities. The increase of Ug raised not only the collision to the magnetic chains but also their mixing tendency with the nonmagnetizable particles. For the given nonmagnetizable particles and Ug, His and Hcs increased as the size or density of the magnetizable particles decreased, indicating that it was more difficult for the segregation to occur and complete. Additionally, the smaller/lighter the magnetizable particles, the steeper the variations of His and Hcs with Ug. A much stronger magnetic field was required for more of such magnetizable particles to form the desired magnetic chains and keep the desired size. Segregation could only be postponed but completely prevented under the magnetization-LAST operation mode however the two types of particles were matched.

The effects of magnetic field intensity on the magnetic properties of Fe80Si9B11 amorphous alloys during magnetic annealing

Magnetic field annealing is an important method to enhance the magnetic properties of amorphous alloys. In this work, the effects of magnetic field annealing intensity on the magnetic properties, mechanical properties, and microstructure of Fe80Si9B11 amorphous ribbons were investigated. It can be seen from the results that the magnetic induction at 1600 A/m (B1600), maximum permeability (μm), coercivity (Hc), Elastic modulus (Er), and Hardness were improved with an increase of the magnetic field intensity. When the magnetic annealing intensity was 2.5 × 10−4 T, the B1600, μm, Hc, Er and Hardness of the sample were improved by 9%, 298%, 67%, 23% and 3%, respectively, compared with those of the as-spun sample. TEM results showed that there are some spherical symmetric clusters present in the 653 K × 2.5 × 10−4 T sample. This may be an important reason for the improvement of the magnetic properties. Compared with the 653 K × 1 T sample, the magnetic field intensity of the 653 K × 2.5 × 10−4 T sample was only 0.025%. However, the values of B1600, μm, Hc, Er and Hardness of the latter reached 96%, 82%, 115%, 90% and 94% of the former, respectively. It means that during the magnetic field annealing process, applying only a small magnetic field can obviously enhance the magnetic and mechanical properties of Fe80Si9B11 amorphous alloy. This provides a theoretical basis for the further improvement of the magnetic and mechanical properties of Fe80Si9B11 alloys, and in the energy saving. The reasons for the changes of magnetic and mechanical properties caused by different magnetic field intensities are discussed.

Impact of an External Magnetic Field on Solitary Waves in Quantum Electron–Hole Plasmas of Semiconductors

The propagation of solitary acoustic pulses in magnetized quantum electron–hole plasmas of semiconductors has been studied. The effects of an external magnetic field and quantum terms, including the electrons and holes quantum recoil effects, exchange-correlation force, and the degenerate pressure of charge carriers are considered. Starting from quantum hydrodynamic equations, by using the reductive perturbation method, the Zakharov–Kuznetsov equation is derived. The theoretical model is applied to three types of semiconductors, namely GaAs, GaSb, and InP. It is clear that basic features of solitary acoustic waves are modified significantly by plasma parameters, especially number densities of semiconductors and magnetic field strength. The value of the amplitude and width of solitary waves strongly depends on the type of semiconductors and the propagation angle in a magnetized quantum electron-hole semiconductor plasma. Numerical results reveal that the width of the solitons gets reduced significantly with the increase of the magnetic field intensity while there is no effect on the amplitude of solitary waves. The weakest magnetic field that sets the pulse width to zero belongs to GaAs. Finally, the stability of the pulse soliton solution of the Zakharov–Kuznetsov equation has been discussed, analytically and numerically. The instability growth rate depends on plasma parameters and magnetic field intensity. The present paper can be meaningful in studying non-linear phenomena and instability behaviors in magnetized quantum electron–hole plasmas of semiconductors and the particle and energy transport mechanism in plasma-assisted quantum semiconductor nanodevices.

Thermo-magneto-convection and mechanism of multiple eddy formation due to applied magnetic field in a lid-driven cavity

Magnetohydrodynamic study of eddy formation and heat transfer in a bottom heated two-dimensional lid-driven cavity with the insulated sidewall is reported in this paper. We consider the classic problem of a two-dimensional lid driven cavity in the presence of an applied external magnetic field. In the standard nonlinear Navier–Stokes equation and the energy equation, appropriate terms are added to model the applied magnetic field and thermo-magnetic convection. And we have derived a higher-order numerical scheme that can provide solutions that are fourth-order accurate. The scheme is implemented with suitable fourth-order accurate boundary conditions. The square LDC enclosure is filled with a fluid of Pr = 6.2. The top lid of the cavity is kept moving with constant velocity. The effect of magnetic field on heat transfer and eddy formation is discussed for 0 ≤ Ha ≤ 250, and 103 ≤ Gr ≤ 104 and the results are presented in terms of contour plots of streamlines, isotherms, Lorentz force, and the kinetic energy. The physical mechanism for forming multiple recirculation zones is understood and attributed to two opposite forces acting in the fluid about the center-line of the cavity, which acts like a couple (and hence rotational flow). This is discovered by computing the Lorentz force acting in the entire domain of fluid flow. Similarly, from the computation of kinetic energy of the fluid at all the grid points in the fluid region, it is revealed that conduction is the dominant heat transfer mechanism at higher magnetic fields. At the same time, convection is the prime mode at low magnetic fields. It is ascertained that with an increase in magnetic field intensity, velocity profiles are suppressed, and heat transfer stabilizes, giving rise to the formation of recirculation zones in the cavity.

Application of a Magnetic Field in Saturated Film Boiling of a Magnetic Nanofluid (MNF) under Reduced Gravity

To overcome the problem of abnormally large bubbles and the large reduction of heat flux under low gravity, the computational model of magnetic nanofluid (MNF) boiling flow was used to systematically study the thermodynamic characteristics of an MNF-saturated film boiling with and without the magnetic field. This study found that in the absence of a magnetic field, the decrease of the gravity level makes the bubble size increase and the bubble departure time increase, and the lower the gravity level, the worse the boiling heat transfer. However, after applying the magnetic field, bubble size decreases significantly and the bubble departure time is shortened. As the magnetic field intensity increases, the difference in bubble size and heat transfer characteristics between different gravity levels becomes smaller and smaller, which shows that for the boiling flow of MNF under low gravity levels, applying a magnetic field can effectively avoid the appearance of abnormally large bubbles, enhance heat transfer, and improve the safety of related heat transfer equipment.

Исследование характеристик частичных разрядов в СПЭ-изоляции кабеля с множественными дефектами

The paper simulates the electric field intensity picture in the cable with one and several defects. Modeling has shown that the presence of several closely spaced defects does not lead to an increase in the electric field intensity in comparison with one defect. On the basis of experimental studies, an analysis of defects' number influence on various parameters of partial discharges (PD) is performed. Artificial defects are created in the area of the XLPE-insulated cable termination. The following parameters of PD are measured: the magnitude of the apparent charge, the power (intensity) of partial discharges, the phase-resolved partial discharge (PRPD) patterns, the shape of PD signals. The analysis shows an increase in the number of defects does not affect the characteristics of partial discharges, despite the fact the defects are located in different sections of the cable with distributed parameters. Thus, it can be difficult to quantify defects during cable partial discharge measurements.

Modification of exposure conditions by the magnetic field configuration in helicon antenna-excited helium plasma

Modification of exposure conditions downstream in the diffusion chamber has been performed in helicon antenna-excited helium plasma by adjusting the magnetic field (intensity and geometry). In the inductively coupled mode (H mode), a reduction in ion and heat fluxes is found with increasing magnetic field intensity, which is further explained by the more highly magnetized ions off-axis around the last magnetic field lines (LMFL). However, in helicon wave mode (W mode), the increase in magnetic field intensity can dramatically increase the ion and heat fluxes. Moreover, the effect of LMFL geometry on exposure conditions is investigated. In H mode with contracting LMFL, off-axis peaks of both plasma density and electron temperature profiles shift radially inwards, bringing about a beam with better radial uniformity and higher ion and heat fluxes. In W mode, although higher ion and heat fluxes can be achieved with suppressed plasma cross-field diffusion under converging LMFL, the poor radial uniformity and a small beam diameter will limit the size of samples suitable for plasma irradiation experiments.

Long term sedimentation of an elliptic disc subject to an electrostatic field using smoothed particle hydrodynamics method

A two dimensional incompressible smoothed particle hydrodynamics scheme for long term sedimentation of rising or falling particulates (bubbles, drops or rigid particles) in Newtonian fluids is presented and validated by simulating the sedimentation of a single elliptic disc. The proposed method is then used to simulate the sedimentation of an elliptic disc subject to an external electric field parallel to the gravitational field. A range of electric field intensities, permittivity ratios, blockage ratios and density ratios are covered in this study. The results show that for given blockage and density ratios, the final sedimentation orientation of the ellipse is dependent on a combination of permittivity ratio and electric field intensity, ranging from horizontal to vertical. Compared to non-electrified sedimentation, an increase in electric field intensity and permittivity ratio lead to vertical sedimentation. As the channels grow wider, the presence of electric field leads to faster ellipse descent, regardless of its initial orientation.

Research on stress detection technology of long-distance oil and gas pipeline based on magnetomechanics characteristics

Magnetic memory stress detection technology has broad application prospects in the field of stress detection in long-distance oil and gas pipelines because it supports non-contact and dynamic on-line detection. However, the magnetic memory signal is weak and susceptible to an external magnetic field. A J-A model is established to quantitatively study the distribution characteristics of the magnetic memory signal in the stress concentration area of the pipeline. In this study, the mathematical model of magnetomechanics of the pipeline is established. The variation law of magnetic memory signal in the stress concentration area with the external magnetic field is calculated and analysed. A systematic experimental study is carried out. The results show that the magnetic memory signal linearly changes with stress in the geomagnetic field, and magnetic memory signal characteristics of circumferential stress with internal pressure is larger than the axial one. The amplitude of the magnetic memory signal in the stress concentration area increases with the increase in magnetic field intensity of the weak magnetic field, meantime the magnetic sensitivity decreases. The magnetic memory signal in the stress concentration area of the pipeline in magnetic saturation is covered by the strong magnetic field resulting in an undetected stress concentration area.

Magnetic-field control of near-field radiative heat transfer between graphene-based hyperbolic metamaterials

Due to the optical transitions between non-equidistant quantized Landau levels in an external magnetic field, graphene can be employed to dynamically tune the near-field radiative heat transfer (NFRHT). In this paper, we investigate the magnetic-field control of NFRHT between two graphene-based hyperbolic metamaterials (GHMs). We find that the magnetic field significantly regulates the NFRHT between two GHMs via modifying the intrinsic hyperbolic modes. Specifically, the radiative heat transfer in the low-frequency range is remarkably suppressed for chemical potential of graphene of 0.05 eV accompanied by the splitting of the heat flux peak with the increase in the magnetic field intensity. We also analyze the magnetoresistance effect related to the heat flux, which reaches 78.23% when H = 7 T. Moreover, we find that the effect of the magnetic field on the hyperbolic modes of GHMs is much stronger for lower chemical potentials. We look forward to the applications of our findings in dynamical thermal management at the nanoscale.