Rotating Magnetic Field

This paper deals with the theoretical investigation of the combined effect of magnetic field dependent (MFD) viscosity and rotation on ferroconvection in the presence of dust particles subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linearized stability theory and normal mode analysis method. The cases of stationary convection and oscillatory modes have been discussed. In this paper, an attempt is also made to obtain the sufficient conditions for the non-existence of overstability.

Rotating magnetic field eddy-current (RoFEC) probe for nondestructive evaluation of steam generator tubes in a nuclear power plant offers an alternate method that has compact configuration and higher speed compared to traditional bobbin coil, rotating probe coils, and array probes. This paper investigates the feasibility of the proposed RoFEC eddy-current probe which is composed of three windings excited by three-phase ac current and does not require mechanical rotation of probe. Results of finite-element modeling using reduced magnetic vector potential (RMVP) formulation are presented for modeling the inspection of ferromagnetic and nonferromagnetic tubes. Design parameters of the excitation coils and GMR pick-up sensor are optimized by means of a parametric study.

This paper presents a new type of eddy current transducer, send-receiver type, using the rotating magnetic field method. The forward problem was solved, the experimental results obtained for detection of different types of degradation have proved the capability to emphasize blisters, and garter springs location and tilt as well as hydrogen content.

During designing a new axial flux permanent magnet free rod rotor synchronous motor, it is important to know before hand in which phase the largest angular velocity can occur, what is the ways to reduce the power consumption, how to achieve to increase or decrease the rotation speed by changing the core geometry. Therefore, presenting these preliminary information that are necessary for the design of a free rod rotor synchronous motor to the researchers is the aim of this work. In this respect, this study presents the design and geometrical dimensions of the stator for a new synchronous motor which is an axial flux permanent magnet free rod machine with three, four, five and six phases. This type of motors are an innovative approach especially for the applications used in industrial stirrers. Each type of stator is designed such that it has an appropriate number of phases. The rotating magnetic field over the stator is established by a PIC based microcontroller feeding the interface circuit to the stator wounds. The maximum angular speeds of bar magnet rotors with four different lengths and masses are calculated theoretically and determined experimentally. In addition, the effects of the distance between the rotor and stator, the angular speed of the rotor within the limits of the operation, and the volume of the liquid to be stirred to the power applied are investigated. Furthermore, the effects of the lengths and angular speeds of the bar magnet rotors to the distance between the rotor and stator are determined. In the light of the information obtained and taking into account the power used, the most appropriate parameters and variables such as the stator geometry changing with the phase used, the length of rotor, the distance between the rotor and stator and the angular speeds of rotor are determined.► This study presents the design and geometrical dimensions of the stator for a new synchronous motor. ► The maximum angular speeds of bar magnet rotors are calculated theoretically and determined experimentally. ► In order to decrease the power consumption, it is necessary to operate the motor with low speeds. ► The distance of rotor–stator is not related to the power consumption and the number of phases.

During the detached Bridgman growth of semiconductor crystals, the melt has a short free surface, which is detached from the ampul wall near the crystal–melt interface, thus eliminating the crystal defects caused by contact with the ampul wall. Recent modeling has indicated that initiation and continuation of detached growth depends on the rate of transport of dissolved gas from the crystal–melt interface, where gas is rejected into the melt, to the detached free surface, where evaporating gas maintains the pressure on the free surface. Here we use numerical modeling to investigate whether the application of a rotating magnetic field increases or decreases the transport of rejected gas to the detached free surface. Unfortunately, the results show that a rotating magnetic field almost always decreases the evaporation rate at the detached free surface. The exception is an insignificant increase for a short period at the beginning of crystal growth for a few circumstances. The evaporat...

This paper presents the design of an AC loss experiment using nitrogen boil-off method. This experiment is aimed at exploring the AC loss of HTS double race-track coils which will be installed on the rotor of a wind turbine generator. The operating environment is simulated by designing a cryostat with rotating magnetic field windings. Apart from the fact that the alternating magnetic field causes most of AC loss on the HTS coils, we also believe that the DC background field would be another important factor causing AC loss if the HTS coil is experiencing by both alternating magnetic field in the perpendicular direction and DC background field in the parallel direction. In order to perform the boil-off measurement, we present the method to estimate the heat leakage in the cryostat which might cause errors to the measurement .

We present several independent in-situ measurements, which provide evidence that charged dust in the E-ring interacts collectively with the dense surrounding plasma disk of Saturn, i.e., form a system of dust-plasma interaction. The results are based on data sampled by the Radio and Plasma Wave Science (RPWS) investigation onboard Cassini, which allows for interferometry of plasma density inhomogeneities (δn/n) with two antenna elements and a Langmuir probe sensor. The interferometer experiment detects two ion populations; one co-rotating with the planetary magnetic field and another moving with near Keplerian speed around Saturn. The full range of RPWS measurements indicates that the Keplerian population consists of colder ions (Ti<few eV), which would interact with the electrical potential cavities associated with the few volts negatively charged E-ring water-rich dust grains. The presence of the charged dust inhibits E×B pick-up of freshly ionized particles by the rotating magnetic field of Saturn, since the local potential gradients near the dust grains are stronger than the large-scale co-rotation electric field. Even so, most ions are eventually energised to energies above the dust potentials of a few volts and become part of a hotter co-rotating ion population. The observed results have direct relevance to the interactions occurring in planet forming accretion disks around young stars, since the physical environment is similar.

The magnetic field dependent viscosity (magnetoviscosity) of dilute suspensions of spherical magnetic particles suspended in a Newtonian fluid subjected to both magnetic and shear flow fields was studied through Brownian dynamics simulations. Results are presented for the response of these suspensions to oscillating magnetic fields and magnetic fields that are corotating or counter-rotating with respect to the fluid vorticity. A decrease in negative values in the intrinsic magnetoviscosity is observed for oscillating and corotating magnetic fields, whereas an increase is observed for counter-rotating magnetic fields. The frequency corresponding to zero viscosity and the minimum value in the negative viscosity are lower for corotating magnetic fields than for oscillating magnetic fields. In the negative magnetoviscosity regions the particles in a corotating magnetic field rotate faster than in an oscillating magnetic field. It is estimated that the flow due to corotating particles could be strong enough to obtain a negative effective viscosity in dilute suspension. Moreover, it is shown that the commonly accepted constitutive equation for the antisymmetric stress describes well the intrinsic magnetoviscosity of the suspension.

During the detached Bridgman growth of semiconductor crystals, the melt has a short free surface, which is detached from the ampul wall near the crystal–melt interface, thus eliminating the crystal defects caused by contact with the ampul wall. Recent modeling has indicated that initiation and continuation of detached growth depends on the rate of transport of dissolved gas from the crystal–melt interface, where gas is rejected into the melt, to the detached free surface, where evaporating gas maintains the pressure on the free surface. Here we use numerical modeling to investigate whether the application of a rotating magnetic field increases or decreases the transport of rejected gas to the detached free surface. Unfortunately, the results show that a rotating magnetic field almost always decreases the evaporation rate at the detached free surface. The exception is an insignificant increase for a short period at the beginning of crystal growth for a few circumstances. The evaporat...

Electromagnetic stirring provides an attractive approach to control the melt flow in metallurgy and crystal growth. Recently, the combination of rotating and travelling magnetic fields has received much interest. While the laminar flow driven by the individual fields is well investigated, the turbulent regime and the effects of superposition are largely unexplored. The paper presents numerical simulations for different combinations of rotating and travelling fields. The numerical model is based on the low-frequency / low-induction limit and employs a spectral element - Fourier method for spatial discretisation. Our results indicate that a travelling field superimposed to a rotating magnetic field leads to an intensification of swirl and secondary flow on one side, opposed by an even more significant breaking effect on the other side. A direct numerical simulation performed for stronger forcing revealed a similar scenario for the turbulent case. NOMENCLATURE