Effect of an External Oriented Magnetic Field on Entropy Generation in Natural Convection (original) (raw)
Related papers
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...
Thermal Science, 2010
A 3-D orig i nal nu mer i cal study of en tropy gen er a tion in the case of liq uid metal lam i nar nat u ral con vec tion in a dif fer en tially heated cu bic cav ity and in the presence of an ex ter nal mag netic field or thogo nal to the iso ther mal walls is car ried out. The ef fect of this field on the var i ous types of irreversibilities is an a lyzed. It was observed that in the pres ence of a mag netic field the gen er ated en tropy is dis trib uted on the en tire cav ity and that the mag netic field lim its the 3-D char ac ter of the dis tribu tion of the gen er ated en tropy. 2 2 2 T J J J s e x y z
Evanescent magnetic field effects on entropy generation at the onset of natural convection
Sadhana, 2010
This paper numerically investigates the effect of an externally evanescent magnetic field on total entropy generation in a fluid enclosed in a square cavity by using a control volume finite element method to solve the conservation equations at Prandtl number of 0•71. The values of relaxation time of the magnetic field are chosen, so that the Lorentz force acts only in the transient state of entropy generation in natural convection. The total entropy generation was calculated for, fixed value of irreversibility distribution ratio, different relaxation time varying from 0 to 1/5 and Grashof number varying from 10 4 to 10 5. The effects of the Hartman number and the magnetic field inclination angle on the evolution of total entropy generation throughout the transient regime were investigated. Results show that the application of evanescent magnetic field not only suppresses the fluctuation of the total entropy generation in the transient state, but also reduces the gap for magnetic field relaxation time less than 1/10.
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.
Journal of Applied Fluid Mechanics, 2016
In this paper, we study the combination between the inclinations of the enclosure and the magnetic field orientation on the oscillatory natural convection. For this, a cylindrical enclosure filled with electrically conducting fluid, has an aspect ratio equal to 2, and subjected to a vertical temperature gradient and different uniform magnetic field orientations were considered. The finite volume method is used to discretize the equations of continuity, momentum and energy. Our computer program based on the SIMPLER Algorithm has a good agreement with available experimental and numerical results. The time-dependent flow and temperature field are presented in oscillatory state, for different cases: inclination of the cylinder, under the effect of magnetic field in different orientations (δ = 0°, 30°, 45° and 90°) and the combination between them. The results are presented at various inclinations of the cylinder (φ = 0°, 30° and 45°), and the Hartmann numbers Ha ≤ 50. The stability diagrams of the dependence between the complicated situations with the value of the critical Grashof number Grcr and corresponding frequency Frcr, are established according to the numerical results of this investigation. The combination between the studied state has a significant effect on the stabilization of the convective flow, and shows that the best stabilization of oscillatory natural convection is obtained at the inclination of the cylinder φ = 30°, and the applied of radial magnetic field (δ = 0°).
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...
Magnetic field effects on natural convection flow of a non-Newtonian fluid in an L-shaped enclosure
Journal of Thermal Analysis and Calorimetry, 2018
The effect of magnetic field on natural convection heat transfer in an L-shaped enclosure filled with a non-Newtonian fluid is investigated numerically. The governing equations are solved by finite-volume method using the SIMPLE algorithm. The power-law rheological model is used to characterize the non-Newtonian fluid behavior. It is revealed that heat transfer rate decreases for shear-thinning fluids (of power-law index, n \ 1) and increases for shear-thickening fluids (n [ 1) in comparison with the Newtonian ones. Thermal behavior of shear-thinning and shear-thickening fluids is similar to that of Newtonian fluids for the angle of enclosure a \ 60°and a [ 60°, respectively. Keywords Magnetohydrodynamics (MHD) Á Natural convection Á Newtonian fluid Á Non-Newtonian fluid Á Enclosure List of symbols AR Aspect ratio B o Magnetic induction (T) g Gravitational acceleration (m s-2) Ha Hartmann number K Thermal conductivity (W m-1 K-1) L Specific length (m) n Power-law index Nu Local Nusselt number P Pressure (Pa) Pr Prandtl number Ra Rayleigh number Re Reynolds number T Wall temperature (K) u Velocity in x-direction (m s-1) v Velocity in y-direction (m s-1) U Dimensionless velocity in x-direction V Dimensionless velocity in y-direction x Distance along x-coordinate y Distance along y-coordinate Greek letters b Thermal expansion coefficient (k-1) l Dynamic viscosity (kg m-1 s-1) q Density (kg m-3) h Dimensionless temperature
Entropy Generation in Heat and Mass Transfer in Porous Cavity Subjected to a Magnetic Field
2012
Numerical investigation is carried out to predict the entropy generation for combined natural convection heat and mass transfer in a two dimensional porous cavity subjected to a magnetic field. The Darcy model is used in the mathematical formulation of the flow in porous media. The mathematical model is derived in dimensionless form. The governing parameters arise in the mathematical model are the Rayleigh number, Lewis number, buoyancy ratio and Hartmann number. The entropy generation is obtained as a function of velocity, temperature, concentration gradients and the physical properties of the fluid. The results are presented as average Nusselt number, Sherwood numbers and dimensionless form of local entropy generation rate for different values of the governing parameters.The numerical results show that increasing the magnetic field parameter (Hartmann number) leads to reduce the flow circulation strength in the cavity and this leads to a decrease in the rate of entropy generation.
Magnetic field effects on entropy generation in heat and mass transfer in porous cavity
the mathematical formulation of the fluid flow in porous media. The mathematical model is derived in dimensionless form and the governing equations are solved using the finite volume method. The governing parameters arise in the mathematical model are the Rayleigh number, Lewis number, buoyancy ratio and Hartmann number. The results are presented as average Nusselt number ( Nu ), Sherwood numbers ( Sh ) and dimensionless form of local entropy generation rate (N s ) for different values of the governing parameters. The numerical results show that increasing the magnetic field parameter (Hartmann number) leads to deterioration of the flow circulation strength in the cavity and this leads to a decrease in the rates of the heat and mass transfer as well as the rate of entropy generation. The results show a stagnate fluid everywhere in the cavity when the buoyancy forces generated due to temperature and concentration differences are in the same order and opposite directions. In this case, the values of Nu , Sh and N s are the minimum. Increasing or decreasing the value of the buoyancy ratio parameter leads to enhance the fluid circulation and hence increase the values of Nu , Sh and N s . The average Sherwood number can be increased with increasing Lewis number. It is observed that the strength of the fluid circulation in the cavity is reduced by increasing the Lewis number. This leads to the decrease in the average Nusselt number and the entropy generation by increasing Lewis number.