Nonuniform Electrical Conductivity Research Articles

Magnetic Machine Perception for Reconstruction of Nonuniform Electrical Conductivity Based on Eddy Current Model

This article presents a machine-perception method based on eddy current density (ECD) field induced in a plate for reconstructing nonuniform electrical conductivity. Formulated as a two-stage inverse problem using distributed current source models, the ECD field is reconstructed from its magnetic flux density and followed by solving an inverse ECD model to estimate the conductivity fields of the plate and its features. Along with a parametric study, the effects of different sensor and coil configurations on the reconstruction accuracy are numerically investigated. The proposed method is evaluated experimentally by comparing two methods: mechanical scanning using a single-sensor and a linear method with a sensitivity matrix. The findings demonstrate that using a sensor-array with a multicoil configuration effectively reduces the number of mechanical scans when making measurements, and eliminates variations below the coil center where the ECD is small.

Numerical study of the MHD flow around a bounded heating cylinder: Heat transfer and pressure drops

This work studies numerically the flow around an electrically insulated heating cylinder, bounded by walls of non-uniform electrical conductivity and subjected to a transversal magnetic field, with non-null components in the toroidal and poloidal directions. The configuration is representative of a typical breeding blanket segment in tokamak fusion reactors: to minimize magnetohydrodynamic (MHD) pressure drops, the liquid metal can be employed just as tritium breeder, whereas a non-conductive secondary fluid is used as coolant. The coolant is carried in the breeding zone by pipes that, being transversal to the stream-wise direction, affect the flow features and heat transfer. The flow is investigated by simulations performed in a 3D domain for Reynolds number 20 and 40, 0≤M≤50 for the Hartmann number and 0°≤α≤32° for the magnetic field inclination on the toroidal axis. The transition to the MHD regime causes the suppression of the cylinder wake and the disappearance of the steady vortex structures. Electromagnetic coupling balances the flow rates between the top and bottom sub-channels, individuated by the cylinder. The flow pattern modifications affect the heat transfer, which is found to increase with both M and α in the considered range, albeit for the latter in a non-monotonic trend. The pressure drop in the channel exhibits a similar behaviour. Moreover, it is dominated by the fully developed component due to the 2D currents, whereas the cylinder pressure drop contribution decreases steadily with the intensity of the applied magnetic field. The simulations were performed with ANSYS CFX-15.

Heat Transfer Enhancement of MHD Flow by Conducting Strips on the Insulating Wall

Due to the magnetohydrodynamic (MHD) effect, which degrades heat transfer coefficients by pulsation suppression of the external magnetic field, on the electrically conducting flow, the wall with nonuniform electrical conductivity is employed in a MHD-flow system for heat transfer enhancement. The nonuniform electrical conductivity distribution of the channel wall could create alternate Lorentz forces along the spanwise direction, which can effectively produce flow disturbance, promote mixture, reduce the thickness of the boundary layer, and enhance heat transfer. So, the heat transfer performances enhanced by some conducting strips aligned with the mean flow direction on the insulating wall for free surface MHD flow are simulated numerically in this paper. The flow behaviors, heat transfer coefficients, friction factors, and pressure drops are presented under different Hartmann numbers. Results show that in the range of Hartmann numbers 30≤Ha≤100, the wall with nonuniform conductivity can achieve heat transfer enhancements (Nu/Nu0) of about 1.2–1.6 relative to the insulating wall, with negligible friction augmentation. This research indicates that the modules with three or five conducting strips can obtain better enhancement effect in our research. Particularly, the heat transfer augmentation increases monotonically with increasing Hartmann numbers. Therefore, the enhancement purpose for high Hartmann number MHD flow is marked, which may remedy the depressing heat transfer coefficients by the MHD effect.

Magnetic control of flow past a blunt body: Numerical validation and exploration

Computational and theoretical studies of a Mach 5 flow over a hemisphere were carried out to validate a new computer code for magnetogasdynamic simulation, and to examine the possibility of heat transfer mitigation through magnetic control. Sample calculations were made using a local solution developed by W. B. Bush [J. Aerosp. Sci. 25, 685 (1958); 28, 610 (1961)] for the stagnation point flow over an axisymmetric blunt body with an imposed dipole magnetic field. Numerical computations, which obviated many of the simplifications inherent in the Bush theory, were carried out employing the low magnetic Reynolds number approximation. Both models indicate that an imposed dipole field can slow the flow in the conductive shock layer and consequently reduce the wall heat flux in the vicinity of the stagnation point. The theoretical model predicts a slightly higher level of heat transfer than that obtained computationally, but there is good agreement between the two models in the fractional change in heat transfer with increasing strength of the applied magnetic field. For both models, nonuniform electrical conductivity was found to reduce the effectiveness of a given applied field. Magnetic flow control is seen to have a sound physical basis, and may prove to be a useful technology for heat transfer mitigation.