Magnetohydrodynamic Natural Convection Heat Transfer Research Articles

Magnetohydrodynamic Natural Convection Heat Transfer of Hybrid Nanofluid in a Square Enclosure in the Presence of a Wavy Circular Conductive Cylinder

Abstract In this paper, steady natural convective heat transfer and flow characteristics of Al2O3-Cu/water hybrid nanofluid filled square enclosure in the presence of magnetic field has been investigated numerically. The enclosure is equipped with a wavy circular conductive cylinder. The natural convection in the cavity is induced by a temperature difference between the vertical left hot wall and the other right cold wall. The steady 2-D equations of laminar natural convection problem for Newtonian and incompressible mixture are discretized using the finite volume method. The effective thermal conductivity and viscosity of the hybrid nanofluid are calculated using Corcione correlations taking into consideration the Brownian motion of the nanoparticles. A numerical parametric investigation is carried out for different values of the nanoparticles volumic concentration, Hartmann number, Rayleigh number, and the ratio of fluid to solid thermal conductivities. According to the results, the corrugated conductive block plays an important role in controlling the convective flow characteristic and the heat transfer rate within the system.

Numerical investigation of magnetohydrodynamic natural convection heat transfer and entropy generation in a rhombic enclosure filled with Cu-water nanofluid

The present work analyses magnetohydrodynamic natural convection heat transfer and entropy generation in rhombic enclosures filled with Cu-water nanofluids. Numerical simulations were executed for varying Rayleigh number (Ra) in the range 103–106, Hartmann number (Ha) in the range 0–100 and inclination angles of the enclosure (30°, 45° and 60°) considering three different volume fractions of the nanofluid (1%, 3% and 5%). The results indicate that at low Ra, the heat transfer rate remains invariant with the variation in Ha. At high Ra (≥105), the presence of the magnetic field is more perceptible implying that the reduction in heat transfer rate with the increase in magnetic field intensity is far more significant. The heat transfer rate enhances with the increase in inclination angle for all Ha for Ra =103 and 104. However, at high Ra (=105 and 106) the trend becomes contrasting due to the interplay of buoyancy and Lorentz forces. There exists an operating range of Ha in the convection regime wherein the efficacy of the nanofluid in augmenting the heat transfer rate is negated when compared to the corresponding performance of the base fluid. The concomitant thermal identity resulting due to the combined interactions of Hartmann number and volume fraction of the nanofluid have been presented. The entropy generation rate decreases with the increase in Ha for all values of Ra and inclination angles of the enclosure.

Effects of Magnetohydrodynamics on Natural Convection and Entropy Generation with Nanofluids

The paper presents a numerical study of the magnetohydrodynamic natural convection heat transfer of a heated block situated on the bottom wall of an enclosure filled with nanofluids. The transport equations for a Newtonian fluid are solved numerically using the lattice-Boltzmann method. The effective thermal conductivity and viscosity of the nanofluid are calculated by the Koo–Kleinstreuer–Li correlation. The influence of pertinent parameters such as Rayleigh number, solid volume fraction, Hartmann number, magnetic field inclination angle, nanoparticle volume concentration and aspect ratio of the rectangular heated block on the flow, heat transfer characteristics, and entropy generation has been investigated. It is found that the total entropy generation is an increasing function of the Rayleigh number, whereas it is a decreasing function of the Hartmann number. Moreover, the numerical results demonstrate that the average Nusselt number increases steadily but nonlinearly by the augmentation of the nanoparticle volume fraction. Also, the results show that the magnetic field with an inclination angle of has the maximum heat transfer coefficient and total entropy generation.

Lattice Boltzmann simulation of magnetohydrodynamic natural convection heat transfer of Al 2 O 3 –water nanofluid in a horizontal cylindrical enclosure with an inner triangular cylinder

Abstract In this study the lattice Boltzmann method is applied to investigate the effect of magnetic field on natural convection heat transfer of Al 2 O 3 –water nanofluid in a two-dimensional horizontal annulus. In this model, the effect of Brownian motion on the effective thermal conductivity is also considered. The effective thermal conductivity and the effective viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. The effect of nanoparticle volume fraction for the enhancement of heat transfer was examined for several sets of values of Rayleigh and Hartmann numbers. Also, a correlation of the Nusselt number with physical parameters is presented. The obtained results indicate that the value of the maximum stream function decreases with increasing Hartmann number. Furthermore, we notice that the Nusselt number has a direct relationship with the Rayleigh number; but quite the opposite is true with the Hartmann number. The obtained results indicate that the Lattice Boltzmann method with double-population is a powerful approach for the simulation of natural convection heat transfer in nanofluids in regions with curved boundaries.

On the Limits of Validity of the Low Magnetic Reynolds Number Approximation in MHD Natural-Convection Heat Transfer

In the majority of magnetohydrodynamic (MHD) natural-convection simulations, the Lorentz force due to the magnetic field is suppressed into a damping term resisting the fluid motion. The primary benefit of this hypothesis, commonly called the low-R m approximation, is a considerable reduction of the number of equations required to be solved. The limitations in predicting the flow and heat transfer characteristics and the related errors of this approximation are the subject of the present study. Results corresponding to numerical solutions of the full MHD equations, as the magnetic Reynolds number decreases to a value of 10−3, are compared with those of the low-R m approximation. The influence of the most important parameters of MHD natural-convection problems (such as the Grashof, Hartmann, and Prandtl numbers) are discussed according to the magnetic model used. The natural-convection heat transfer in a square enclosure heated laterally, and subject to a transverse uniform magnetic field, is chosen as a case study. The results show clearly an increasing difference between the solutions of the full MHD equations and low-R m approximation with increasing Hartmann number. This difference decreases for higher Grashof numbers, while for Prandtl numbers reaching lower values like those of liquid metals, the difference increases.

Magnetohydrodynamic free convection and entropy generation in a square porous cavity

The problem of entropy generation in a fluid saturated porous cavity for laminar magnetohydrodynamic natural convection heat transfer is analyzed in this paper. Heat transfer results are also presented additionally. Darcy's law for porous media is considered. Magnetic force is assumed acting along the direction of the gravity force. As boundary conditions of the cavity, two vertical opposite walls are kept at constant but different temperatures and the remaining two walls are kept thermally insulated. For a range of Rayleigh number ( Ra=1–10 4) and Hartmann number ( Ha=0–10), heat transfer, overall entropy generation rate, and heat transfer irreversibility are presented in terms of dimensionless Nusselt number ( Nu), entropy generation number ( Ns), and Bejan number ( Be), respectively. Finally, parametric results are presented in terms of isothermal lines, streamlines, isentropic lines, and iso-Bejan lines.

Magnetohydrodynamic natural convection heat transfer from radiate vertical porous surfaces

Magnetohydrodynamic natural convection heat transfer from radiate vertical surfaces with fluid suction or injection is considered. The nonsimilarity parameter is found to be the conductive fluid injection or suction along the streamwise coordinate ξ = V{4x/υ2gβ(Tw – T∞)}1/4. Three dimensionless parameters had been found to describe the problem: the magnetic influence number N = σB2yυ/ρV2, the radiation-conduction parameter Rd = kαR/4aT3∞, and the Gebhart number Gex = gβx/cp to represent the effect of the viscous dissipation. It is found that increasing the magnetic field strength causes the velocity and the heat transfer rates inside the boundary layer to decrease. Its apparent that increasing the radiation-conduction parameter decreases the velocity and enhances the heat transfer rates. The Gebhart number, i.e, the viscous dissipation had no effect on the present problem.

Magnetohydrodynamic natural convection heat transfer from horizontal cylinders

Magnetohydrodynamic natural convection heat transfer from horizontal cylinders