Electrokinetic instability refers to unstable electric field-driven disturbance to fluid flows, which can be harnessed to promote mixing for various electrokinetic microfluidic applications. This work presents a combined numerical and experimental study of electrokinetic ferrofluid/water co-flows in microchannels of various depths. Instability waves are observed at the ferrofluid and water inte...

Based on the momentum and continuity equations for ferrofluid under an applied magnetic field, assuming linear behavior for the magnetic material of the ferrofluid, and using carrying current concentric finite wire magnetic field model, the magnetic force was calculated. A modified Reynolds equation is obtained. It is simultaneously solved with the energy equation numerically by the finite diff...

We report flow instabilities with simultaneous, in-plane-rotating and dc-axial uniform magnetic fields. In uniform dc-axial magnetic fields, a ferrofluid drop in a Hele-Shaw cell with an ,1.0-mm gap forms the familiar labyrinth pattern. With subsequent application of an ,100-G rms in-plane, 20–40-Hz rotating uniform magnetic field, smooth spirals form. If the rotating magnetic field is applied ...

The present study is carried out to investigate the magneto-viscous effects on incompressible ferrofluid flow over a porous rotating disc with suction or injection on the surface of the disc subjected to a magnetic field. The flow under consideration is axi-symmetric steady ferrofluid flow of electrically non-conducting fluid. Karman’s transformation is used to convert the governing boundary la...

A microfluidic pump is described that uses magnetic actuation to push fluid through a microchannel. Operation relies on the use of magnetically-actuated plugs of ferrofluid, a suspension of nanosize ferromagnetic particles. The ferrofluid contacts but is immiscible with the pumped fluid. The prototype circular design demonstrates continuous pumping by regenerating a translating ferrofluidic plu...

Ferrofluids have been vastly wooed in diverse areas of engineering and research. This contribution briefly exposes some concepts specific to ferrofluids and how they relate to recent applications emerging in chemical engineering, including mass transfer enhancement, momentum transfer in laminar and turbulent pipe flows and in porous media flows, and the motion of magnetic nanoparticles in gas-l...

The spectral response of a Bragg grating reflector inscribed in a microstructured optical fibre is tuned by employing an infiltrated ferrofluid, while modifying the overlap of the ferrofluidic medium with the grating length. Significant spectral changes in terms of Bragg grating wavelength shift and extinction ratio were obtained under static magnetic field actuation. Spectral measurements reve...

This paper presents an approach to establish the analytical formula for the force acting on a non-magnetic disc plunged into a ferrofluid, due to the effect of a magnetic field gradient generated by the magnetic inductor of the actuator. The expression of the force acting on a magnetizable body placed in a magnetic field was used for the particular conditions imposed by the actuator configurati...

Ferrofluids are strongly paramagnetic liquids. We study the behavior of ferrofluid droplets confined between two parallel plates with a weak applied field parallel to the plates. The droplets elongate under the applied field to reduce their demagnetizing energy and reach an equilibrium shape where the magnetic forces balance against the surface tension. This elongation varies logarithmically wi...

In the present work we report on the behavior of ferrofluid microdrops in an immiscible nonmagnetic carrier fluid and vice versa subjected to the action of magnetic fields. Our experiments evidence previously unexplored instability and flow patterns. We investigated the instabilities initiated by constant magnetic field and by combined action of constant and rotating magnetic fields. The observ...