Increase Of Magnetic Intensity Research Articles

Simulation of magneto mixed convective flow and thermal behavior of hybrid nanofluid in a partially heated wavy cavity

This study is an attempt to address numerically the thermal performance of magneto mixed convection in a wavy cavity filled with Cu-Al2O3(50%–50%) hybrid nanoparticles suspended in water under the influence of magnetic field dependent viscosity. A focus is made on the nonuniform partial heating from the left. The role of geometric parameters on the thermal performance is scrutinized thoroughly by changing surface waviness of the right wall, heating location and the direction of motion of the top and bottom walls. Based on these lid motion, the analysis is conducted by considering four geometrical set up. The transformed governing Navier–Stokes equations in dimensionless form are written in stream function-vorticity and energy transport equations. These equations are solved by using an inhouse computing code written in the compact finite difference approach. This study encompasses the effects of different physical pertinent parameters such as Richardson number, Hartmann number, magnetic orientation, solid concentrations, magnetic number. Simulations show the significant enhancement of thermal performance with the increase of magnetic orientation, undulation of the waviness and solid concentration of nanoparticles while it decreases with the increase in magnetic intensity. It is also seen that Case-I (single wall motion) and Case-III (parallel wall motion) can be an optimal configuration to get the strongest heat transfer inside the partially heated wavy enclosure.

Gd impurity effect on the magnetic and electronic properties of hexagonal Sr ferrites: A case study by DFT

The electronic and magnetic properties of strontium hexa-ferrite (SrFe12O19) are studied in pure state (SrFe12O19) and with dopant in the positions 2 and 3 of Fe atoms (SrGdFe11O19-I and SrGdFe11O19-II, respectively) by utilizing a variety of the density functional theory (DFT) approaches including the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE-GGA) and GGA plus Hubbard U parameter (GGA+U). The pure SrFe12O19 is a hard magnetic half-metal with an integer magnetic moment of 64.00μB, while using the GGA+U functional, the magnetic intensity increases, resulting in a magnetic semiconductor with a high integer magnetic moment of 120μB. By doping the Gd atom in the two different positions of Fe, the magnetic moment is increased to 71.68μB and 68.00μB, respectively. The magnetic moment increases and remains an integer; hence, SrGdFe11O19-II can be very useful for application in magnetic memories. Moreover, applying the Hubbard parameter turns SrGdFe11O19-I and SrGdFe11O19-II to magnetic semiconductors with a magnetic moment of 124μB, and the energy gap of both doped structures at spin down is found to be less than the pure case. By studying the electronic density diagram of the atoms of the crystal, it is found that the major effect to create magnetization in the pure case is due to the Fe atom. However, in the doped case, the elements Gd and Fe have the highest moment in the crystal respectively.

The Influence of a Magnetic Field on Phase Transition in Antiferromagnetic Films: Computer Modeling Research

The influence of an external magnetic field on the phase-transition temperature for antiferromagnetic thin films is investigated. The computer modeling method for the antiferromagnetic Ising model with a thin film geometry is used. Films with thicknesses from 4 to 16 layers have been investigated. It is shown that the temperature of the antiferromagnetic phase transition decreases according to the square law as the external magnetic intensity increases. The rate of decrease of the phase-transition temperature depends on the film thickness and on the relationship between the exchange integrals on the surface and the bulk of the system. For each system, there is a limit value of the magnetic intensity such that no antiferromagnetic phase transition occurs if it is exceeded. The dependence of the limit value of the magnetic intensity on the relationship between the exchange integrals obeys the square law as well.

Influence of critical parameters on an unsteady state MHD flow in a porous channel with exponentially decreasing suction

The behavior of the velocity for a fixed Reynolds number and different values of angle of inclination has been presented in these graphs. In each of these situations, it is noticed that as the magnetic intensity increases, the velocity decreases. Further, as the angle of inclination increases, the velocity decreases. In all these figures, it is observed that there is a wide spread dispersion of velocity profiles which are very closed to boundary plate initially. Further, it is observed that for constant values of magnetic intensity and Reynolds number. As the angle of inclination increases, the velocity decreases. Further, in all above situations the velocity profiles are perfectly parabolic and the no slip conditions are satisfied at both the boundaries. it is seen that as the ‘Re’ increases, the skin friction in the boundary layer region increases. Further, as the angle of inclination of the boundary surface increases, the skin friction decreases and finally converges to zero. For a slight change in the applied magnetic intensity, a marginal change in the skin friction is noticed in the boundary layer region. Also, it is observed that as the angle of inclination increases, the skin friction is observed to be increasing. The nature of profiles in both the cases do not differ qualitatively. For a small change in the applied magnetic intensity, the skin friction decreases. it is seen that as the magnetic field increases, the skin friction varies linearly. As the ‘Re’ increases, the skin friction on the boundary increases. Not much of change in the profiles of the skin friction is noticed.

Rearrangement of liquid metal surface waves by a uniform transverse magnetic field

In the fusion engineering, the liquid metal flows are considered to be an alternative solution against the solid surface in designing the plasma facing components. However, it remains unclear about the magneohydrodynamics influences on the liquid metal flows due to the lacking of experimental observations that the limited measurement method for the opaque liquid metal film should be criticized. In the present study, a laser profilometer based on the laser triangulation technique is adapted to measure the thickness of liquid GaInSn film, while a visualization method is introduced to monitor the topography of the free surface, which is formed on a horizontal substrate in the presence of a uniform transverse magnetic field. We will firstly demonstrate the applicability of a laser profilometer by measuring the thickness of GaInSn in a container with a quasi-static or dynamic free surface, to validate that the result is in good agreement with theoretical data. Using the visualization method and the laser profilometer, the evolutions of free surface waves and the time-dependent film thickness across a fixed line are measured by varying the flow rate and the magnetic field continuously. It is found that, under the influences of transverse magnetic field, the free surface waves are strongly suppressed along the spanwise direction, leaving the surface waves to propagate in the streamwise direction. More quantitatively, the measured thickness of the free surface reveals that a moderate magnetic field tends to decrease the averaged value and the root mean square value of the film thickness fluctuations while a strong magnetic field will conversely increase them. Besides, the dominant fluctuation frequencies of surface wave are observed to decrease with the increase of magnetic intensity, indicating that greater suppression is induced on the motion of small waves by the transverse magnetic field.

The antiwear mechanism of W-20Cu composites in direct current magnetic field

The wear behavior and mechanism of W-20%Cu composites which prepared by powder metallurgy process with using 45# steel in the direct current magnetic field were researched. The results indicated that the wear rate and friction coefficient decreased with the increase of magnetic intensity. According to the SEM observations, the wear mechanism of the W-20Cu composites in the direct current magnetic field was the comprehensive action of abrasive and oxidative wear. Moreover, with or without magnetic field, there are refined grain zone, severely deformed zone and rheological zone basis of the deform degree along the longitudinal section of W-20Cu pin. But the morphology and microstructure of the worn surface and sub-surface were greatly affected by the magnetic field intensity according to the TEM observations. The depth of deformed layer, the fragment of Cu crystals, the dislocations in the grains are different when the magnetic field was added. The improved wear resistance is mainly due to the mobility of dislocations caused by the magnetic field.

Strong temperature dependent viscosity effects on bio-magnetic fluid flow under the action of localized magnetic field and viscous dissipation

In this study consideration has been given to the two-dimensional, unsteady, laminar flow of an electrically conducting bio-fluid (blood) in a rectangular channel. In this model both magnetization and electrical conductivity of blood are taken into account. The viscosity of the fluid is also assumed to be a strong function of temperature. The coupled, nonlinear system of equations are transformed into the stream function-vorticity-temperature formulation. These equations along with the suitable boundary conditions are solved iteratively by using the upwind scheme along with successive over relaxation method. The numerical results obtained here are illustrated in terms of streamlines, vorticity function, velocity component and temperature function contours. The results show that the flow is effected to a great extent owing to the presence of the magnetic source. It is observed that the temperature values increases due to an increase in magnetic intensity for all the contours plotted in this study. It is also noticed that variable viscosity greatly influenced the flow field and generates a lot of vortices within the vicinity of the walls.

Effects of magnetic fields on improving mass transfer in flue gas desulfurization using a fluidized bed

The effects of magnetic fields on improving the mass transfer in flue gas desulfurization using a fluidized bed are investigated in the paper. In this research, the magnetically fluidized bed (MFB) is used as the reactor in which ferromagnetic particles are fluidized with simulated flue gas under the influence of an external magnetic field. Lime slurry is continuously sprayed into the reactor. As a consequence, the desulfurization reaction and the slurry drying process take place simultaneously in the MFB. In this paper, the effects of ferromagnetic particles and external magnetic fields on the desulphurization efficiency are studied and compared with that of quartz particles as the fluidized particles. Experimental results show that the ferromagnetic particles not only act as a platform for lime slurry to precipitate on like quartz particles, but also take part in the desulfurization reaction. The results also show that the specific surface area of ferromagnetic particles after reaction is enlarged as the magnetic intensity increases, and the external magnetic field promotes the oxidation of S(IV), improving the mass transfer between sulphur and its sorbent. Hence, the efficiency of desulphurization under the effects of external magnetic fields is higher than that in general fluidized beds.

Effect of Rotating Magnetic Field on Fluid Convection and Microstructure during Directional Solidification of Sn-Zn Alloy

The solidification behaviors of Sn-Zn alloy under rotating magnetic field (RMF) with different magnetic intensities and different rotating frequencies were investigated, and the velocity of the convection induced by RMF was calculated. It is found that the trunk length of the precipitated phase reduces with the increase of magnetic intensity and rotating frequency, and the precipitated-phase distribution is more uniform. The tangential rate increases with increasing the magnetic intensity and rotating frequency, and reaches the maximum value at about 0.55r0. All the results indicate that the solidification microstructure is attributed to the effect of RMF on the nucleation, temperature fluctuation and fluid convection in the solidification process. It predicts that RMF presents obvious advantages on controlling solidification microstructure.

Preparation of Co–Pt–P thin films by magnetic electrodeposition

Magnetic fields perpendicular to the electric field were applied during an electrodeposition process to obtain Co–Pt–P thin films from alkaline baths. Effects of different current densities and magnetic intensities on the composition, microstructure and magnetic properties of Co–Pt–P thin films were studied. It was found that the deposition rate and films thickness increased gradually with the increase of the current density and magnetic intensity. Almost all of the deposited films were crystalline and showed Co(002), CoPt(111) peaks. With the increase in the magnetic intensity, the intensity of CoPt(111) peak decreased while the intensity of Co(002) rose gradually. Magnetic fields would induce cobalt growing along (002) orientation. The films were densely covered with typical nodular structure. When the current density increased to 100 A m−2, rougher and agglomerate nodular structures would be formed. Films of smaller grain size and smooth surface could be formed under high magnetic intensity (0·5 T) as a result of impact of magnetic force and MHD effects. Furthermore, higher current density induced larger Magnetisation and lower coercivity. Largest coercivity could be achieved when current density equals to 70 A m−2. With the increase in magnetic intensity, cobalt contents in films increase gradually which lead to the rise on magnetisation.

Magnetic electrodeposition of ZnNi alloy films

Magnetic fields parallel to electrodes were introduced during plating process to obtain ZnNi alloy films from acid baths. Effects of different magnetic intensities on the composition, nucleation magnetism, surface morphology and anticorrosion of ZnNi films were investigated. With the increase in magnetic intensity, deposition rate and nickel contents increased gradually due to magnetohydrodynamic (MHD) effects caused by Lorentz force. It was found that magnetic force Fm in the magnetic electrodeposition process could have a significant effect on the mass transfer to dramatically improve deposition rate. Maximum deposition rate (90 m h−1) was achieved when the magnetic intensity was equal to 1 T. The films were densely covered with typical nodular structure. Films of smaller grain size and smooth surface could be formed under high magnetic intensity as a result of Lorentz force and MHD effects. Moreover, ZnNi films obtained with higher magnetic intensity possessed more positive self-corrosion potential and optimal anticorrosion performance. However, much higher nickel contents in ZnNi films may drop anticorrosion performance.

Effect of magnetic fields on pulse plating of cobalt films

Magnetic fields parallel to the electrodes were introduced during a pulse plating process to obtain cobalt thin films from alkaline baths. Effects of different magnetic intensities on the composition, microstructure, and magnetic properties of cobalt thin films were investigated. It was found that the deposition speed increased gradually with the increase of magnetic intensity. Almost all of the deposited films were crystalline and showed Co(002), Co(100) peaks. With the rise on the magnetic intensity, the intensity of Co (002) peak raised gradually. Magnetic fields would induce cobalt growing along (002) orientation. The films were densely covered with typical nodular structure. Films of smaller grain size and smooth surface could be formed under high magnetic intensity (1 T) as a result of magnetic force and MHD effects. Moreover, higher magnetic intensity induced larger saturation magnetization and lower coercivity. With the rise on magnetic intensity, cobalt contents in the films increased gradually, which led to the rise of saturation magnetization.

Experimental Study on Ammonia-Water Bubble Absorption in External Magnetic Field

Absorber is a key component of absorption refrigeration system, in which there is a complicated heat and mass transfer. To improve the performance of absorber, the magnetic field was used as a enhancing way, the experiments of NH3/H2O bubble absorption in magnetic field were carried out. The results showed that the NH3/H2O bubble absorption can be strengthened by the magnetic field. Both AR(absorption rate) and EAR(effective absorption ratio) increase with the increase of magnetic intensity within the range of 0~280mT. The EAR is always higher than 1 when the external magnetic field exists. The EAR reaches the maximum 1.069 when the initial ammonia concentration is 20wt% and the magnetic intensity is 280mT. The primary strengthening mechanisms are also explained.

The effect of magnetic fields on the electroless deposition of Co–W–P film

Magnetic fields perpendicular to the copper substrate were applied during an electroless deposition process to obtain Co–W–P thin films from alkaline baths. Effects of different magnetic intensities, pH values and different powers of ultrasonic on the composition, microstructure and magnetic properties of Co–W–P alloys were investigated. Along with the increase of magnetic intensity, deposition speed and film thickness increased gradually as a result of the impacts of magnetic force and micro-MHD effect. Higher magnetic intensity could improve cobalt atomic percentage in the film and increase magnetization of Co–W–P films. Almost all of the deposited films were crystalline and contained hexagonal cobalt with a preferred crystallographic orientation (002). Dissimilar surface morphology could be detected under different pH values when 0.5 T magnetic intensity was introduced, such as rice-like and needle-like structures. When magnetic field was applied during the electroless deposition, grains of films tended to grow perpendicularly to the substrate and hill-like structures would appear with the increase of magnetic intensity. It was also found out that hill-like structure thin films tended to have high coercivities. Hill-like structures could be smoothed when ultrasonic was applied during magnetic electroless deposition. Maximum coercivity (914 Oe) could be obtained when 90 W ultrasonic and B = 0.5 T were introduced.

Effect of high magnetic fields on the migration of second phases during the solidification of metals

Theoretical analysis shows that the migration behavior of a second phase during solidification processes in a high magnetic field (HMF) can be described by the migration velocity, which is a function of properties of melt matrix and the second phase, magnetic intensity and its gradient, as well as the geometry and size of the second phase. Lorentz force tends to make the second phase distribute homogenously, although its efficiency decreases with the increase of magnetic intensity beyond a certain value. When a gradient HMF is imposed, magnetization force becomes the dominant factor for the migration behavior of second phase. The effect of magnetization force increases with magnetic gradient, while it is difficult to control the migration of a second phase due to the constraint of Lorentz force when magnetic gradient is small. The theory has been experimentally verified by controlling the migration of in situ prepared particles in Al-Si and Al-Ni alloys under HMF conditions.

Fluid flow and microstructure formation in a rotating magnetic field during the directional solidification process

Abstract The influence of the fluid flow driven by rotating magnetic field (RMF) on the solidification microstructures of Sn–Bi alloys was investigated. It is found that, for the Sn–50 wt.% Bi hypoeutectic alloy, the primary phase (Sn) shows a morphology transition from coarse dendrite to equiaxed dendrite, moreover, the grains are fractured and refined with the application of RMF. As for the Sn–65 wt.% Bi hypereutectic alloy, the volume fraction gradient of the primary phases (Bi) at different positions reduces with the increase of magnetic intensity, and the macrosegregation is eliminated effectively. The theoretical calculation indicates that the tangential rate of the fluid flow has a maximum value at 0.55 r 0 , which is three magnitudes larger than the radial component. Furthermore, the microstructure formation mechanisms under the RMF condition were analyzed on basis of the calculation results and solidification theories.

Influence of rotating magnetic field on the formation of solidification microstructure

The solidification microstructures of Pb-45%Sn hypoeutectic alloy in rotating magnetic field (RMF) were investigated. When the rotating frequency keeps constant，the grain size reduces linearly with the increase of magnetic intensity，and structure of the primary phase changes from the dendrite to spherical crystals. X-ray diffraction (XRD) measurement indicates that the RMF causes the lattice expansion of primary phase (Pb)，and the lattice parameter increases at first and then decreases with the increase of RMF intensity. Therefore，there is a critical value of magnetic intensity. Moreover，the Sn content in primary phase (Pb)reduces gradually with the increase of magnetic intensity. The results are analyzed theoretically based on electromagnetism field theory and scattering law. It is revealed that RMF causes severe fluid flow，and accelerates the diffusion of solute atom and heats the melt，which results in the increase of nucleation rate and the decrease of growth velocity of crystal.

Magnetic intensity affects cryptochrome-dependent responses in Arabidopsis thaliana

Cryptochromes are blue-light absorbing photoreceptors found in many organisms where they have been involved in numerous growth, developmental, and circadian responses. In Arabidopsis thaliana, two cryptochromes, CRY1 and CRY2, mediate several blue-light-dependent responses including hypocotyl growth inhibition. Our study shows that an increase in the intensity of the ambient magnetic field from 33-44 to 500 muT enhanced growth inhibition in A. thaliana under blue light, when cryptochromes are the mediating photoreceptor, but not under red light when the mediating receptors are phytochromes, or in total darkness. Hypocotyl growth of Arabidopsis mutants lacking cryptochromes was unaffected by the increase in magnetic intensity. Additional cryptochrome-dependent responses, such as blue-light-dependent anthocyanin accumulation and blue-light-dependent degradation of CRY2 protein, were also enhanced at the higher magnetic intensity. These findings show that higher plants are sensitive to the magnetic field in responses that are linked to cryptochrome-dependent signaling pathways. Because cryptochromes form radical pairs after photoexcitation, our results can best be explained by the radical-pair model. Recent evidence indicates that the magnetic compass of birds involves a radical pair mechanism, and cryptochrome is a likely candidate for the avian magnetoreception molecule. Our findings thus suggest intriguing parallels in magnetoreception of animals and plants that appear to be based on common physical properties of photoexcited cryptochromes.

Collagen production and maturation at the experimental ligament defect stimulated by pulsing electromagnetic fields in rabbits.

Eighty rabbits receiving the square resection (4 x 4 mm) of both patellar ligaments in full thickness at their center were divided into 4 groups, and each group (20 rabbits) were electromagnetically stimulated with different magnetic intensities, 0 (control group), 2, 10, or 50 gauss (G), for 6 hr daily. Pulse frequency and pulse width were 10 Hz and 25 microseconds, respectively. Five animals of each group were sacrificed weekly from 1st to 4th week after operation and the defect tissue was collected for biochemical and ultrastructural evaluations. Before sacrificing, the blood flow of the central portion of patellar defects were measured. Significant increases in blood flow at the defect were observed in 50 G group compared to those of other groups from 2 to 4 weeks after operation. The collagen content in PEMFs groups showed a significant increase compared to that of control group. Furthermore, those increases were higher according to the increase in magnetic intensity. Electronmicroscopically, massive developmental rough endoplasmic reticulum was seen in the fibroblasts at 2 weeks after operation in 50 G group compared to other groups, which suggests the more active collagen production in this group. These results suggest that PEMFs enhanced the blood flow and increased the fibroblasts at the defect. At the same time, PEMFs directly stimulated the collagen production from the fibroblasts, thus accelerate the healing process of the ligament.

Marine magnetic study in the northeast Chukchi Sea

During the 1961 and 1962 field seasons, the U. S. Coast and Geodetic Survey conducted sea magnetometer operations off the northwest coast of Alaska. Tracklines, primarily oriented in a north-south direction and spaced at intervals of 10 km or less, provided adequate coverage for the delineation of prominent magnetic anomalies. A distinct change in character of the residual magnetic intensity contours occurs at about 165°30′W. Very little magnetic relief exists east of this longitude, but, to the west, a north-south trending magnetic feature with anomalies of up to 450 gammas was mapped. The feature appears to be more closely related to north-south structures associated with the Tigara uplift than to the east-west trends of the Colville geosyncline. The increase in magnetic intensity is interpreted as a shallowing of the basement surface that indicates a northern continuation of the Tigara uplift.