Hartmann number

About: Hartmann number is a research topic. Over the lifetime, 2593 publications have been published within this topic receiving 61342 citations.

MHD forced convection of MWCNT–Fe3O4/water hybrid nanofluid in a partially heated τ-shaped channel using LBM

Abstract: Forced convection heat transfer of multi-wall carbon nanotubes–iron oxide nanoparticles/water hybrid nanofluid (MWCNT–Fe3O4/water hybrid nanofluid) inside a partially heated τ-shaped channel has been numerically investigated. The effect of magnetic field is taken into account. The governing equations are solved by the lattice Boltzmann method in the domain, and the results were compared with other numerical methods by an excellent agreement between them. The effects of parameters such as Hartmann number (0 ≤ Ha ≤ 60), volume fraction of nanoparticles (0 ≤ ϕ ≤ 0.003) and different location of two heaters on the fluid flow and heat transfer are studied. The results indicate that for all cases, the average Nusselt number of each heater increases as the volume fraction of nanoparticles increases. The heat transfer characteristics were significantly affected by the arrangement of the two heaters. The heaters located on the left half of the top wall is convection-dominant mechanism, and the conduction heat transfer is the primary mechanism when the heater is on the right half of the top wall. The average Nusselt number increases as Ha increases for the heater of dominating convection mechanism but decreases for the heater of dominating conduction mechanism.

MHD mixed convection of nanofluid in a flexible walled inclined lid-driven L-shaped cavity under the effect of internal heat generation

Abstract: In this study, mixed convective flow of nanofluid in an inclined L-shaped cavity which has elastic walls is numerically analyzed under the effects of internal heat generation and magnetic field by using the finite element technique with the Arbitrary-Lagrangian–Eulerian method. Simulations are performed for different values Richardson number (between 0.03 and 30), inclination angle of the cavity (between 0°and 180°), Hartmann number (between 0 and 50), orientation angle of the magnetic field (between 0°and 90°), internal Rayleigh number (between 1 0 4 and 1 0 6 ), solid nanoparticle volume fraction (between 0 and 0.04), flexible wall elastic modulus (between 1 0 4 and 1 0 8 ) and aspect ratio (between 0.2 and 0.7) of the L-shaped cavity. It was observed that the effects of elastic wall on the convective heat transfer features are significant for the lowest value of Richardson number and lowest values of elastic modulus while 11% of discrepancy is obtained in the average Nusselt number when cavity with elastic and rigid walls is compared. The impact of the magnetic inclination angle is significant when compared to magnetic field strength for the variation of the average Nusselt number. Cavity inclination angle has significant impacts on the variation of the average Nusselt number for water and nanofluid. A higher size of the cold wall (aspect ratio) increases the heat transfer rate while the internal Rayleigh number reduces it. Enhancement in the average Nusselt number is about 15%–19% at highest nanoparticle volume fraction of the nanofluid while the trends in the convective heat transfer features with respect to changes in the pertinent parameters are similar for water and nanofluid.

Magnetohydrodynamic flow in a right-angle bend in a strong magnetic field

Abstract: The magnetohydrodynamic (MHD) flow through sharp 90° bends of rectangular cross-section, in which the flow turns from a direction almost perpendicular to the magnetic field to a direction almost aligned with the magnetic field, is investigated experimentally for high values of the Hartmann number M and of the interaction parameter N. The bend flow is characterized by strong three-dimensional effects causing a large pressure drop and large deformations in the velocity profile. Since such bends are basic elements of fusion reactors, the scaling laws of magnetohydrodynamic bends flows with the main flow parameters such as M and N as well as the sensitivity to small magnetic field inclinations are of major importance. The obtained experimental results are compared to those of an asymptotic theory.In the case where one branch of the bend is perfectly aligned with the magnetic field good agreement between the results obtained by the asymptotic model and by the experiments was found at high M ≈ 8 × 10 and N ≈ 105 for pressure as well as for electric potentials on the duct surface. At lower values of N a significant influence of inertia has been detected. The pressure drop due to inertial effects was found to scale with N−1/3. The same – 1/3-power dependency on N has been found in the vicinity of the bend for the electric potentials at walls aligned with the magnetic field. At walls with a significant normal component of the field an influence neither of the Hartmann number nor of the interaction parameter has been found. This suggests that the inertial part of the pressure drop arises from inertial side layers, whereas the core flow remains inertialess and inviscid. A variation of the Hartmann number is of negligible influence compared to inertia effects with respect to pressure drop and surface potential distribution. The viscous part of the pressure drop scales with M−½.Changes of the magnetic field orientation with respect to the bend lead in general to different flow patterns in the duct, because the electric current paths are changed. The inertia–electromagnetic interaction determines the magnitude of the inertial part of the pressure drop, which scales with N−1/3 for any magnetic field orientation. The dependence of the pressure drop on M remains proportional to M−½. With increasing M and N the measured data tend to those predicted by the asymptotic model. Local measurements within the liquid metal exhibit discrepancies with the model predictions for which no adequate explanation has been found. But they show that below a critical interaction parameter flow regions exist in which the flow is time dependent. These regions are highly localized, whereas the flow in the rest of the bend remains steady.