Entropy Generation Study of MHD Thermosolutal Convection in a Square Cavity for Different Prandtl Numbers (original) (raw)
Related papers
2011
Thermosolutal convection in a square cavity filled with air and submitted to an inclined magnetic field is investigated numerically. The cavity is heated and cooled along the active walls with a mass gradient whereas the two other walls of the cavity are adiabatic and insulated. Entropy generation due to heat and mass transfer, fluid friction and magnetic effect has been determined in transient state for laminar flow by solving numerically the continuity, momentum energy and mass balance equations, using a Control Volume Finite-Element Method. The structure of the studied flows depends on four dimensionless parameters which are the Grashof number, the buoyancy ratio, the Hartman number and the inclination angle. The results show that the magnetic field parameter has a retarding effect on the flow in the cavity and this lead to a decrease of entropy generation, Temperature and concentration decrease with increasing value of the magnetic field parameter.
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.
Energy Conversion and Management, 2014
Entropy generation associated with laminar natural convection in an infinite square cavity, subjected to an isotropic heat field with different intensities; was numerically investigated for different values of Rayleigh number. The numerical work was carried out using, an in-house CFD code written in FORTRAN, which discretizes non-dimensional forms of the governing equations using the finite volume method and solves the resulting system of equations using Gauss-Seidal method utilizing a TDMA algorithm. Proper code validation was undertaken in order to establish the entropy generation calculations. It was found that the increase in the isotropic heat field intensity resulted in a corresponding exponential increase of the entropy augmentation number, and promoted high values of Bejan number within the flow. The entropy generation due to heat transfer was approximately one order of magnitude higher than the entropy generation due to fluid friction. The spatial uniformity of the Bejan number was more sensitive to the change in Rayleigh number than to the heat field intensity. The thermodynamic penalty of the isotropic heat field is shown by means of global integrals of the entropy source terms over the entire flow domain.
2016
The numerical simulation of entropy generation at mixed natural free and forced convection flow in a square lid-driven cavity filled with an eletrically conducting binary fluids saturated porous media in the presence of a magnetic field is performed in this investigation. Both the top and bottom horizontal walls of the cavity are kept at constant and different temperatures while the left and right vertical walls are adiabatic and insulated. The magnetic field is applied in normal direction to the cavity. The Darcy model, including Brinkman term relative to viscous effects and Forchheimer term due to inertial forces, is used for the momentum equations, and the SIMPLER algorithm, based on the control volume finite-element method approach is used to solve the pressure –velocity coupling. The flow pattern and the heat transfer characteristics inside the cavity are presented in the form of isotherms, streamlines and isentropic lines and average Nusselt number trend. The entropy gen...
International journal of applied thermodynamics, 2021
Magnetohydrodynamic (MHD) mixed convection and entropy generation in a C-shaped cavity filled by an electrically conducting fluid are investigated numerically using the finite volume method and the SIMPLE algorithm. In this work, we focus on the effect of the magnetic field on the characteristics of fluid flow, heat transfer and entropy generation for various values of Richardson number (Ri = 0.1, 1 and 10), Hartmann number (0 ≤ Ha ≤ 200), tilting angle (α); ranging from-45° to +45°, and aspect ratio (AR = 0.3, 0.5 and 0.7). The results show an increase in the average Nusselt number and the entropy generation by increasing the aspect ratio (AR), whereas they decrease when Ha number increases, independently of α and Ri. At high values of Ha number, the conduction state is the dominant mode of heat transfer regardless of Ri, AR and α. Moreover, the total entropy generation is mainly due to the irreversibility of heat transfer whatever the control parameters are.