Sharif Digital Repository

We study the dynamics of a conducting fluid carrying (i) a uniform current in the presence of a non-uniform magnetic field or (ii) carrying a non-uniform current in the presence of a uniform magnetic field, using particle image velocimetry (PIV). Our results show that the average angular velocity of the induced rotation has a power-law dependence on the electric current passing through the fluid with an exponent ≈2/3, in excellent agreement with our simulation results, for the same system. To explain the experimental observations we explore all possibilities for inducing rotation in a fluid carrying an electric current. Our theoretical discussion indicates two scenarios wherein applying... 

This paper presents the effects of a non-uniform magnetic field on the hydrodynamic and thermal behavior of ferrofluid flow in a wavy channel by 3D numerical simulation. The wavy surfaces at the top and bottom of the channel are heated by constant heat fluxes. Moreover, the sidewalls are adiabatic. In the wavy section, in the perpendicular direction of the main flow, the magnetic field that linearly varies along the direction of the main flow is applied. The mathematical model that is consistent with the principles of ferrohydrodynamics and magnetohydrodynamics is used for the problem formulation. The results indicate that the wavy wall enhances the heat transfer rate on the bottom of the... 

Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power source is utilized to mix two fluids. One of these active methods is magnetic micromixers using ferrofluid. In this technique, magnetic nanoparticles are used to make one phase responsive to magnetic force, and then by applying a magnetic field, two fluid phases, one of which is magneto-responsive, will sufficiently mix. In this study, we investigated the effect of the magnetic field’s characteristics... 

The Smoothed Particle Hydrodynamics (SPH) method is extended to solve magnetostatic problems involving magnetically interacting solid bodies. In order to deal with the jump in the magnetic permeability at a fluid-solid interface, a consistent SPH scheme is utilized and a modified formulation is proposed to calculate the magnetic force density along the interface. The results of the magnetostatic solver are verified against those of the finite element method. The governing fluid flow equations are discretized using the same SPH scheme, developing an efficient method for simulating the motion of paramagnetic solid bodies in a fluid flow. The proposed algorithm is applied to a benchmark problem... 

In this article, a three-dimensional numerical simulation is performed to investigate the effect of magnetic field on the heat transfer of ferrofluid inside a tube which is equipped with twisted tape. This work comprehensively focused on the flow feature and temperature distribution of ferrofluid in presence of non-uniform magnetic field while ferrofluid swirled inside a tube with twisted tape. In this study, it is assumed that the ferrofluid is single phase and laminar and constant heat flux is applied on the outside of the tube. The magnetic field is established by wire in parallel direction with the axis of the tube. The base fluid is water with 0.86 Vol% Nano particles (Fe3O4). The... 

In this article, the effects of nonuniform magnetic fields on the hydrodynamics and heat transfer from a heated sphere to its surrounding ferrofluid flow have been investigated. Kelvin body forces originate from the nonuniformity of the applied magnetic field and can generate the vortices behind the sphere leading to a considerable change in the velocity and temperature fields. The applied magnetic field disturbs the thermal boundary layer and decreases heat-transfer resistance, leading to a significant enhancement in the heat-transfer coefficient. Variations of the local and average Nusselt number value (Nu), separation angle, recirculation length, and drag coefficient were considered to...