Article Analysis of the Magnetic Field Effect on Entropy Generation at Thermosolutal Convection in a Square Cavity (original) (raw)
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2009
This paper investigates the effect of an imposed magnetic field on the flow patterns, and the entropy generation in a square cavity. A control volume finite element method is used to solve the conservation equations at Prandtl number of 0.71. The effects of Grashof number, Hartmann number and inclination angle of the magnetic field are investigated. The study covers the range of the Hartmann number from 0 to 50, the magnetic field inclination angle from 0° to 90° with Grashof number ranging between 10^3 and 10^5. The effects of Hartmann number and the magnetic field inclination angle are presented graphically in terms of isotherm and streamline plots. The effect of the magnetic field is found to suppress the convection currents and heat transfer inside the cavity. This effect is significant for high Grashof numbers. Results show that the Nusselt number is clearly affected by the magnetic field. The effect of the Hartmann number on entropy generation was investigated in steady-unstea...
2011
Natural and thermosolutal convections in a confined cavity filled with air is numerically investigated. The cavity is heated and cooled along the active walls whereas the two other walls of the cavity are adiabatic and insulated. Entropy generation due heat and mass transfers, fluid friction and magnetic effect has been determined in transient state laminar flow by solving numerically: the continuity, momentum and energy equations, using a Control Volume Finite Element Method. The structure of the studied flows depends on six dimensionless parameters which are: the thermal Grashof number, the inclination angle, the irreversibility distribution ratio and the aspect ratio of the cavity. In the presence of a magnetic and radiative effects, two others dimensionless parameters are used which are Hartmann number and Radiation parameter. The obtained results show that entropy generation tends towards asymptotic values for lower thermal Grashof number values, whereas it takes an oscillative...
The present study is devoted to the problem of onset of oscillatory instability in convective flow of an electrically conducting fluid under an externally imposed time-independent uniform magnetic field. Convection of a low-Prandtl-number fluid in a laterally heated two-dimensional horizontal cavity is considered. Fixed values of the aspect ratio ͑length/heightϭ4͒ and Prandtl number ͑Prϭ0.015͒, which are associated with the horizontal Bridgman crystal growth process and are commonly used for benchmarking purposes, are considered. The effect of a uniform magnetic field with different magnitudes and orientations on the stability of the two distinct branches ͑with a single-cell or a two-cell pattern͒ of the steady state flows is investigated. Stability diagrams showing the dependence of the critical Grashof number on the Hartmann number are presented. It is shown that a vertical magnetic field provides the strongest stabilization effect, and also that multiplicity of steady states is suppressed by the electromagnetic effect, so that at a certain field level only the single-cell flows remain stable. An analysis of the most dangerous flow perturbations shows that starting with a certain value of the Hartmann number, single-cell flows are destabilized inside thin Hartmann boundary layers. This can lead to destabilization of the flow with an increase of the field magnitude, as is seen from the stability diagrams obtained. Contrary to the expected monotonicity of the stabilization process with an increase of the field strength, the marginal stability curves show nonmonotonic behavior and may contain hysteresis loops.
Journal of Applied Fluid Mechanics, 2016
In this study natural convection heat transfer fluid flow and entropy generation in a porous inclined cavity in the presence of uniform magnetic field is studied numerically. For control of heat transfer and entropy generation, one or two partitions are attached to horizontal walls. The left wall of enclosure is heated with a sinusoidal function and right wall is cooled isothermally. Horizontal walls of the enclosure are adiabatic. The governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. The influence of Hartmann number, inclination angle, partition height, irreversibility distribution ratio, and partition location is investigated on the flow and heat transfer characteristics and the entropy generation. The obtained results indicated that the partition, magnetic field and rotation of enclosure can be used as control elements for heat transfer, fluid flow and entropy generation in porous medium.
Magneto-thermocapillary-buoyancy convection in a square cavity with partially active vertical walls
Thermal Science
Effect of magnetic field on combined surface tension and buoyancy convection in an enclosure with partially active vertical walls is investigated numerically. The active part of the left side wall is at a higher temperature than the active part of the right side wall. The bottom and the inactive parts of the side walls are adiabatic and capillary forces occur at the top free surface. The governing equations are discretized by the finite volume method. The results are obtained for Pr = 0.054, 0 ? Ha ? 100, 0 ? Ma ? 10000, and 2.104 ? Gr ? 2.106. The flow structure and temperature field were presented by streamlines and isotherms respectively. The surface tension effect of is manifested by increasing Marangoni number. The application of magnetic field was found to control the flow and to oppose the capillary effects.
Effect of a Magnetic Field on Buoyancy-Driven Convection in Differentially Heated Square Cavity
IEEE Transactions on Magnetics, 2009
Steady, laminar, natural-convection flow in the presence of a magnetic field in a cavity heated from left and cooled from right is considered. In our formulation of the governing equations, mass, momentum, energy and induction equations are applied to the cavity. To solve the governing differential equations a finite volume code based on PATANKAR's SIMPLER method is utilized. Numerical predictions are obtained for a wide range of Rayleigh number (Ra) and Hartmann number (Ha) at the Prandtl number Pr = 0 733. When the magnetic field is relatively strengthened, the thermal field resembles that of a conductive distribution, and the fluid in much of the interior is nearly stagnant. Further, when the magnetic field is weak and the Rayleigh number is high, the convection is dominant and vertical temperature stratification is predominant in the core region. However, for sufficiently large Ha, the convection is suppressed and the temperature stratification in the core region diminishes. The numerical results show that the effect of the magnetic field is to decrease the rate of convective heat transfer and the average Nusselt number decreases as Hartmann number increases. The results are presented for Rayleigh number from 10 4 up to 10 6 and are in form of streamlines, isotherms, and Nusselt number for various Rayleigh and Hartman numbers.
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Effect of an External Oriented Magnetic Field on Entropy Generation in Natural Convection
Entropy, 2010
The influence of an external oriented magnetic field on entropy generation in natural convection for air and liquid gallium is numerically studied in steady-unsteady states by solving the mass, the momentum and the energy conservation equations. Entropy generation depends on five parameters which are: the Prandtl number, the irreversibility coefficients, the inclination angle of the magnetic field, the thermal Grashof and the Hartmann numbers. Effects of these parameters on total and local irreversibilities as well as on heat transfer and fluid flow are studied. It was found that the magnetic field tends to decrease the convection currents, the heat transfer and entropy generation inside the enclosure. Influence of inclination angle of the magnetic field on local irreversibility is then studied.