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11 – 20 of over 9000The purpose of this paper is to investigate how the new theory on the general systemic yoyos can be plausibly employed to provide novel explanations for some of the well‐known…
Abstract
Purpose
The purpose of this paper is to investigate how the new theory on the general systemic yoyos can be plausibly employed to provide novel explanations for some of the well‐known laboratory experiments of physics and how a different theory that is more refined than the currently accepted theories can be established for illustrating phenomena that have not been completely explainable by using the traditional theories.
Design/methodology/approach
The general field structures of systemic yoyos, combined with some of the well‐known laboratory observation of physics, are employed as the basic methodology for the current paper.
Findings
Owing to the co‐existence of magnetic fields and ring‐shaped negative electric fields, all possible ways for an electromagneton to be fired into a stable, uniform‐intensity magnetic field are investigated. How such an electromagneton could be traveling under the mutual influence of the fields is described with details.
Originality/value
The value of this paper lies on the fact that it points out a brand new and practically applicable theory for looking at some of the well‐recorded phenomena of electromagnetism.
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Mojtaba Sepehrnia, Hossein Khorasanizadeh and Mohammad Behshad Shafii
This paper aims to study the thermal and thermo-hydraulic performances of ferro-nanofluid flow in a three-dimensional trapezoidal microchannel heat sink (TMCHS) under uniform heat…
Abstract
Purpose
This paper aims to study the thermal and thermo-hydraulic performances of ferro-nanofluid flow in a three-dimensional trapezoidal microchannel heat sink (TMCHS) under uniform heat flux and magnetic fields.
Design/methodology/approach
To investigate the effect of direction of Lorentz force the magnetic field has been applied: transversely in the x direction (Case I);transversely in the y direction (Case II); and parallel in the z direction (Case III). The three-dimensional governing equations with the associated boundary conditions for ferro-nanofluid flow and heat transfer have been solved by using an element-based finite volume method. The coupled algorithm has been used to solve the velocity and pressure fields. The convergence is reached when the accuracy of solutions attains 10–6 for the continuity and momentum equations and 10–9 for the energy equation.
Findings
According to thermal indicators the Case III has the best performance, but according to performance evaluation criterion (PEC) the Case II is the best. The simulation results show by increasing the Hartmann number from 0 to 12, there is an increase for PEC between 845.01% and 2997.39%, for thermal resistance between 155.91% and 262.35% and ratio of the maximum electronic chip temperature difference to heat flux between 155.16% and 289.59%. Also, the best thermo-hydraulic performance occurs at Hartmann number of 12, pressure drop of 10 kPa and volume fraction of 2%.
Research limitations/implications
The embedded electronic chip on the base plate generates heat flux of 60 kW/m2. Simulations have been performed for ferro-nanofluid with volume fractions of 1%, 2% and 3%, pressure drops of 10, 20 and 30 kPa and Hartmann numbers of 0, 3, 6, 9 and 12.
Practical implications
The authors obtained interesting results, which can be used as a design tool for magnetohydrodynamics micro pumps, microelectronic devices, micro heat exchanger and micro scale cooling systems.
Originality/value
Review of the literature indicated that there has been no study on the effects of magnetic field on thermal and thermo-hydraulic performances of ferro-nanofluid flow in a TMCHS, so far. In this three dimensional study, flow of ferro-nanofluid through a trapezoidal heat sink with five trapezoidal microchannels has been considered. In all of previous studies, in which the effect of magnetic field has been investigated, the magnetic field has been applied only in one direction. So as another innovation of the present research, the effect of applying magnetic field direction (transverse and parallel) on thermo-hydraulic behavior of TMCHS is investigated.
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Fatih Selimefendigil, Hakan F. Öztop and Ali J. Chamkha
Numerical study of nanofluid forced convection within a branching channel was performed under the influence of a uniform magnetic field. The purpose of this study is to enhance…
Abstract
Purpose
Numerical study of nanofluid forced convection within a branching channel was performed under the influence of a uniform magnetic field. The purpose of this study is to enhance the heat transfer performance of the separated flow at the branching channel with the use of magnetic field and nanofluid. The use of magnetic field and enhancement in both the thermal conductivity and electrical conductivity with the inclusion of the nanoparticles provides favorable thermophysical properties of the nanofluid when it used as a heat transfer fluid in a branching channel. The results of this study may be used to control the thermal performance in a branching channel and further optimization studies in the presence of magnetic field.
Design/methodology/approach
Galerkin weighted residual finite element method was used for the simulations. The numerical simulation results are performed by changing the inclination angle of the lower branching channel (between 0° and 90°), thermophysical properties of the fluid via inclusion of nanoparticles (between 0 and 0.04), Reynolds number (between 100 and 400) and magnetic field strength (Hartmann number changes between 0 and 15).
Findings
It was observed that the recirculation zones and reattachment length of the upper and lower branching channels are affected by the variation of those parameters. Reattachment lengths increase with the augmentation of the Reynolds number and deterioration of the Hartmann number. Average Nusselt number becomes higher for higher values of Hartmann number and solid particle volume fraction. Inclusion of the nanoparticle to the base fluid is very effective for the configuration with higher values of Hartmann number. An optimum value of the inclination angle of the lower branching channel is observed, beyond which heat transfer rate is significantly reduced due to the establishment of a large vortex in the upper branching channel and restriction of the fluid motion.
Originality/value
In this study, forced convection of nanofluid flow in a branching channel under the effect of magnetic field was numerically studied. Magnetic field effects with nanoparticle inclusion to the base fluid on the convective heat transfer was analyzed for various inclination angles of the lower branching channel. Flow separation at the junction of the channels and thus convective heat transfer rate are influenced by the variation of these parameters. There are many studies related to application of the magnetic field with nanofluids, and a few of them are related to configurations with separated flows. To the best of the authors’ knowledge, there exist no studies for the application of nanofluids and magnetic field for the convective heat transfer in a branching channel. This topic is of importance as there are many engineering applications of the branching channels.
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Marcin Ziolkowski and Stanislaw Gratkowski
In many different engineering fields often there is a need to protect regions from electromagnetic interference. According to static and low-frequency magnetic fields the common…
Abstract
Purpose
In many different engineering fields often there is a need to protect regions from electromagnetic interference. According to static and low-frequency magnetic fields the common strategy bases on using a shield made of conductive or ferromagnetic material. Another screening technique uses solenoids that generate an opposite magnetic field to the external one. The purpose of this paper is to discuss the shielding effect for a magnetic and conducting cylindrical screen rotating in an external static magnetic field.
Design/methodology/approach
The magnetic flux density is expressed in terms of the magnetic vector potential. Applying the separation of variables method analytical solutions are obtained for an infinitely long magnetic conducting cylindrical screen rotating in a uniform static transverse magnetic field.
Findings
Analytical formulas of the shielding factor for a cylindrical screen of arbitrary conductivity and magnetic permeability are given. A magnetic Reynolds number is found to be an appropriate indication of the change in magnetic field inside the screen. Useful simplified expressions are presented.
Originality/value
This paper treats in a qualitative way the possibility of static magnetic field shielding by using rotating conducting magnetic cylindrical screens. Analytical solutions are given. If the angular velocity is equal to zero or the relative permeability of the shield is equal to one the shielding factor has forms well known from literature.
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Mohammad Sadak Ali Khan, A. Suresh and N. Seetha Ramaiah
The purpose of this paper is to evaluate the performance of the semi-active fluid damper. It is recognized that the performance of such a damper depends upon the magnetic and…
Abstract
Purpose
The purpose of this paper is to evaluate the performance of the semi-active fluid damper. It is recognized that the performance of such a damper depends upon the magnetic and hydraulic circuit design. These dampers are generally used to control the vibrations in various applications in machine tools and robots. The present paper deals with the design of magneto-rheological (MR) damper. A finite element model is built to analyze and understand the performance of a 2D axi-symmetric MR damper. Various configurations of damper with modified piston ends are investigated. The input current to the coil and the piston velocity are varied to evaluate the resulting change in magnetic flux density (B), magnetic field (H), field dependent yield stress and magnetic force vectors. The simulation results of the various configurations of damper show that higher magnetic force is associated with plain piston ends. The performance of filleted piston ends is superior to that of other configurations for the same magnitude of coil current and piston velocity.
Design/methodology/approach
The damper design is done based on the fact that mechanical energy required for yielding of MR fluid increases with increase in applied magnetic field intensity. In the presence of magnetic field, the MR fluid follows Bingham’s plastic flow model, given by the equation τ = η γ•+τ y (H) τ > τ y . The above equation is used to design a device which works on the basis of MR fluid. The total pressure drop in the damper is evaluated by summing the viscous component and yield stress component which is approximated as ΔP = 12ηQL/g3W + CτyL/g, where the value of the parameter, C ranges from a minimum of 2 (for ΔPτ ΔPη less than approximately 1) to a maximum of 3 (for ΔPτ/ΔPη greater than approximately 100). To calculate the change in pressure on either side of the piston within the cylinder, yield stress is required which is obtained from the graph of yield stress vs magnetic field intensity provided by Lord Corporation for MR fluid −132 DG.
Findings
In this work, three different finite element models of MR damper piston are analyzed. The regression equations, contour plots and surface plots are obtained for different parameters. This study can be used as a reference for selecting the parameters for meeting different requirements. It is observed from the simulation of these models that the plain ends model gave optimum magnetic force and 2D flux lines with respect to damper input current. This is due to the fact that the plain ends model has more area when compared with that of other models. It is also observed that filleted ends model gave optimum magnetic flux density and yield stress. As there is reduced pole length in the filleted ends model, the MR fluid occupies vacant area, and hence results in increased flux density and yield shear stress. The filleted ends assist the formation of dense magnetic flux lines thereby increasing the flux density and yield stress. This implies that higher load can be carried by the filleted ends damper even with a smaller size.
Originality/value
This work is carried out to manufacture different capacities of the dampers. This can be applied as vibration controls.
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Mohammadhossein Hajiyan, Shohel Mahmud, Mohammad Biglarbegian, Hussein A. Abdullah and A. Chamkha
The purpose of this paper is to investigate the convective heat transfer of magnetic nanofluid (MNF) inside a square enclosure under uniform magnetic fields considering…
Abstract
Purpose
The purpose of this paper is to investigate the convective heat transfer of magnetic nanofluid (MNF) inside a square enclosure under uniform magnetic fields considering nonlinearity of magnetic field-dependent thermal conductivity.
Design/methodology/approach
The properties of the MNF (Fe3O4+kerosene) were described by polynomial functions of magnetic field-dependent thermal conductivity. The effect of the transverse magnetic field (0 < H < 105), Hartmann Number (0 < Ha < 60), Rayleigh number (10 <Ra <105) and the solid volume fraction (0 < φ < 4.7%) on the heat transfer performance inside the enclosed space was examined. Continuity, momentum and energy equations were solved using the finite element method.
Findings
The results show that the Nusselt number increases when the Rayleigh number increases. In contrast, the convective heat transfer rate decreases when the Hartmann number increases due to the strong magnetic field which suppresses the buoyancy force. Also, a significant improvement in the heat transfer rate is observed when the magnetic field is applied and φ = 4.7% (I = 11.90%, I = 16.73%, I = 10.07% and I = 12.70%).
Research limitations/implications
The present numerical study was carried out for a steady, laminar and two-dimensional flow inside the square enclosure. Also, properties of the MNF are assumed to be constant (except thermal conductivity) under magnetic field.
Practical implications
The results can be used in thermal storage and cooling of electronic devices such as lithium-ion batteries during charging and discharging processes.
Originality/value
The accuracy of results and heat transfer enhancement having magnetic field-field-dependent thermal conductivity are noticeable. The results can be used for different applications to improve the heat transfer rate and enhance the efficiency of a system.
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Shichao Jiang, Xinliang Lu, Hongliang Wang, Kai Song and Yuanyuan Jiang
Detection of hidden defects of aluminum alloy plate with damping coating is a challenging problem. At present, only a few non-destructive testing methods exist to address this…
Abstract
Purpose
Detection of hidden defects of aluminum alloy plate with damping coating is a challenging problem. At present, only a few non-destructive testing methods exist to address this engineering problem. Without the restriction of skin effect, remote field eddy current (RFEC) overcomes the interference caused by the damping coating. The RFEC, which has potential advantages for detecting the hidden defects of aluminum plate with damping coating, can penetrate the metal plate to detect buried depth defects. This study aims to test how thick the RFEC sensor can penetrate the metal plate to detect the buried defects.
Design/methodology/approach
The magnetic field distribution characteristics are analyzed, the magnetic field intensity distribution is calculated, and the structure and parameters of the coil, magnetic circuit and shielding damping are determined through the two- and three-dimensional finite element simulation methods. Optimal excitation frequency is obtained, and the distance between the excitation coil and detection coil is determined by analyzing the relationship between excitation frequency and remote field points.
Findings
Simulation and experimental results verify the feasibility of applying the RFEC detection technology in detecting the hidden defects of aluminum alloy plate with damping coating.
Originality/value
In this paper, the RFEC testing model of hidden defects in aluminum plate sample with damping coating is established by using the finite element method.
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Xian Zhang, Zhaoyang Yuan, Yang Qingxin, Zhaohui Wang, Hao Meng and Yao Jin
The purpose of the paper is to analyze the impact of coupling on the distribution of the magnetic field and study the characteristics of the magnetic flux density in the…
Abstract
Purpose
The purpose of the paper is to analyze the impact of coupling on the distribution of the magnetic field and study the characteristics of the magnetic flux density in the transmission process of the magnetic coupling resonant wireless power transmission (MCR-WPT) system, which provides guidance on the design of the WPT system.
Design/methodology/approach
In this study, a finite element simulation analysis was conducted and a three-dimensional (3D) electromagnetic field measurement platform was used.
Findings
It is shown that the distribution of the magnetic field, as well as the position of maximum magnetic flux density, will change when the coils are coupled. The simulation results of the magnetic field distribution, as well as the transmission performance, are different from those in practice. It cannot describe the actual performance of WPT system.
Originality/value
A 3D electromagnetic field measurement system and the host computer software are designed to help optimize the simulation and carry out more accurate and efficient research. The 3D electromagnetic field measurement system can be used to study the distribution of the spatial electromagnetic field, influencing factor, exposure and interoperability between different coils.
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Jan Kotlarz, Romana Ratkiewicz and Wojciech Konior
This paper aims to demonstrate the impact of interstellar (IS) magnetic field on stellar shocks existence, shape and size in the stellar wind (SW) vs interstellar medium (ISM…
Abstract
Purpose
This paper aims to demonstrate the impact of interstellar (IS) magnetic field on stellar shocks existence, shape and size in the stellar wind (SW) vs interstellar medium (ISM) numerical models.
Design/methodology/approach
Comparison of hydrodynamics (HD) and magnetohydrodynamic (MHD) models results with or without ISM magnetic field, its intensity and ISM parameters.
Findings
ISM magnetic field facilitates formation and stabilises bow shocks around all astrophysical objects. ISM magnetic field may also be one of the reasons for a bow shock existence around the Sun.
Practical implications
ISM magnetic field should be implemented in MHD and future kinetic numerical models of the SW interaction with ISM plasma.
Originality/value
This paper presents the results of HD and MHD models of bow shocks and the importance of ISM magnetic field implementation, according to astronomical bow shock observations. The study also presents a review of the most important papers showing the numerical results of bow shock formation.
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Zhu Feng, Shaotao Zhi, Lei Guo, Chong Lei and Yong Zhou
This paper aims to investigate magnetic field anneal in micro-patterned Co-based amorphous ribbon on giant magneto-impedance (GMI) effect enhancement.
Abstract
Purpose
This paper aims to investigate magnetic field anneal in micro-patterned Co-based amorphous ribbon on giant magneto-impedance (GMI) effect enhancement.
Design/methodology/approach
The amorphous ribbons were annealed in transverse and longitudinal magnetic field. The influence of different field annealing directions on GMI effect and impedance Z, resistance R and reactance X with a series of line width have been deeply analyzed.
Findings
In comparison with GMI sensors microfabricated by unannealed and transversal field annealed ribbons, GMI sensor which was designed and microfabricated by longitudinal field anneal ribbon performs better. The results can be explained by the domain wall motion and domain rotation during annealing process and the geometric structure of Co-based GMI sensor. In addition, shrinking the line width of GMI sensor can promote GMI effect significantly because of the effect of demagnetizing field, and the optimum GMI ratio is 209.7 per cent in longitudinal field annealed GMI sensor with 200 μm line width.
Originality/value
In conclusion, annealing in longitudinal magnetic field and decreasing line width can enhance GMI effect in micro-patterned Co-based amorphous ribbon.
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