Numerical study of a single droplet falling through a nonuniform horizontal magnetic field with a constant gradient

Abstract A numerical study of magneto-hydrodynamic mixed convection in a cavity has been conducted to investigate the influence of magnetic field on integrated flux of thermal energy, linear momentum, and kinetic energy. Shear force through lid motion establishes the forced convection effect and buoyancy force due to differential heating of the moving lid and the stationary interface ensures the natural convection phenomenon. Additionally, conduction through the solid slab with prescribed temperature at the outer surface attached to the cavity induces conjugate heat transfer. Further, the top and bottom walls throughout the domain are kept insulated and a uniform horizontal magnetic field is applied on the interface toward left. Fluid flow and heat transfer characteristics are examined for a range of Hartmann number (Ha): 0, 10, 50, and 120 at fixed values of Reynolds number, Grashof number, and Prandtl number of 300, 9 × 104 and 0.71, respectively. The result shows that the transport of heat in the near wall regions of the fluid domain is primarily governed by diffusion, whereas advection appears stronger in the central region of the cavity. Increase in magnetic field strength from Ha = 0 to 120 gradually suppresses the recirculating structure of the flow signifying a reduction in advective strength as depicted by the decrease in the value of total integrated heat flux from 25.15×10-3 to 6.0×10-3. The reduction in heat flux, momentum fluxes, and kinetic energy fluxes with increase in magnetic field has been well correlated in the range of 0≤Ha≤120.

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A numerical study of a bubble pair rising side by side in external magnetic fields

Journal of Fluid Mechanics ◽

10.1017/jfm.2021.695 ◽

2021 ◽

Vol 926 ◽

Author(s):

Jie Zhang ◽

Ming-Jiu Ni

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Lorentz Force ◽

Stokes Equations ◽

Numerical Study ◽

Three Dimensional ◽

Transverse Field ◽

Asymmetric Distribution ◽

Streamwise Vortices ◽

Horizontal Magnetic Field

The motion of a pair of bubbles rising side by side under the influence of external magnetic fields is numerically examined. Through solving the fully three-dimensional Navier–Stokes equations, the results reveal that the bubble interactions are rather sensitive to the field direction and strength. At first, we identify that, in a hydrodynamic flow, whether the two bubbles will bounce or coalesce depends on the developments of the counter-rotating streamwise vortices during the collision. In particular, for an originally bouncing bubble pair, a streamwise magnetic field tends to promote their coalescence by weakening the strengths of the standing streamwise vortices, and such a weakening effect is caused by the asymmetric distribution of the Lorentz force in the presence of another bubble such that a torque is induced to offset the original streamwise vortices. Under a horizontal magnetic field, on the other hand, the influences are highly dependent on the angle between the bubble centroid line and the field: a transverse field or a moderate spanwise field always leads the bubble pair to coalescence while a strong spanwise field has the opposite effect. This anisotropic effect comes from the Lorentz force induced flow diffusion along the magnetic field, which not only produces two pairs of streamwise vortices at the bubble rear, but also homogenizes the pressure along the magnetic lines. As the competition between the two mechanisms varies with the magnetic direction and strength, the interaction between the bubble pair also changes. We show that the external magnetic fields control the bubble interaction through reconstructing the vortex structures, and hence the core mechanisms are identified.

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Numerical study of single droplet impact onto liquid metal film under a uniform magnetic field

Physics of Fluids ◽

10.1063/1.4903821 ◽

2014 ◽

Vol 26 (12) ◽

pp. 122107 ◽

Cited By ~ 8

Author(s):

Jin-Jin Wang ◽

Jie Zhang ◽

Ming-Jiu Ni ◽

René Moreau

Keyword(s):

Magnetic Field ◽

Liquid Metal ◽

Metal Film ◽

Uniform Magnetic Field ◽

Numerical Study ◽

Droplet Impact ◽

Single Droplet

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Numerical Study of Natural Convection of Biological Nanofluid Flow Prepared from Tea Leaves under the Effect of Magnetic Field

Processes ◽

10.3390/pr9101824 ◽

2021 ◽

Vol 9 (10) ◽

pp. 1824

Author(s):

Yacine Khetib ◽

Ahmad Alahmadi ◽

Ali Alzaed ◽

Hussein A. Saleem ◽

Mohsen Sharifpur ◽

...

Keyword(s):

Magnetic Field ◽

Numerical Study ◽

Control Volume ◽

Simple Algorithm ◽

Tea Leaves ◽

Nanofluid Flow ◽

Horizontal Magnetic Field ◽

Side Walls ◽

Strong Convection ◽

Glycol Solution

The heat transfer of a biological nanofluid (N/F) in a rectangular cavity with two hot triangular blades is examined in this work. The properties used for nanoparticles (N/Ps) are derived from a N/P prepared naturally from tea leaves. Silver N/Ps are distributed in a 50–50 water/ethylene glycol solution. The cavity’s bottom wall is extremely hot, while the upper wall is extremely cold. The side walls are insulated, and the enclosure is surrounded by a horizontal magnetic field (M/F). The equations are solved using the control volume technique and the SIMPLE algorithm. Finally, the Nu is determined by changing the dimensions of the blade, the Rayleigh number (Ra), and the Hartmann number (Ha). Finally, a correlation is expressed for the Nu in the range of parameter changes. The results demonstrate that an increment in the Ra from 103 to 105 enhances the Nu more than 2.5 times in the absence of an M/F. An enhancement in the strength of the M/F, especially at the Ra of 105, leads to a dramatic reduction in the Nu. An increase in the height of the triangular blade intensifies the amount of Nu in weak and strong convection. The enlargement of the base of the triangular blade first enhances and then decreases as the Nu. The addition of 5% silver biological N/Ps to the fluid enhances the Nu by 13.7% in the absence of an M/F for high Ras.

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