Dynamics of Active Bubbles in a Magnetic Fluid in an Inhomogeneous Magnetic Field

Purpose. To develop a method for generating active bubbles and droplets containing a non-magnetic core and a shell of magnetic fluid, as well as to study the influence of the magnetic field on their dynamics.

Methods. The experiments were carried out on an experimental setup for studying the dynamics of droplet and bubble flow in magnetic liquids, developed based on known methods. An annular permanent magnet placed on top of an electromagnet was used as a source of an inhomogeneous magnetic field. A permanent magnet was used to study the effect of an external magnetic field on the dynamics of bubbles or droplets. The supply of the non-magnetic phase into the channel was carried out using a syringe pump. The dynamics of droplet and bubble flows were recorded by the passing light of the illuminator using a high-speed camera (Nikon 1).

Results. Studies of the dynamics of active bubbles and droplets formed in an inhomogeneous field of an annular magnet were carried out by injection a non-magnetic phase into a magnetic liquid. The influence of the magnetic field configuration on the velocity, acceleration, and size of active droplets has been studied. The phenomenon of selforganization of bubbles on the surface of the oil layer and the influence of an external magnetic field on the resulting inclusions are shown.

Conclusion. During the experiment, it was found that the separation of non-magnetic droplets and bubbles occurs from a levitating non-magnetic volume. The size and dynamics of bubbles and droplets can be controlled using an external magnetic field. As the current increases, the droplet velocity increases, the acceleration decreases, and the size decrease. This is due to a change in the configuration of the field created by the combined magnetic field source. With the phenomenon of self-organization of non-magnetic bubbles covered with a magnetic shell, it can be noticed that their diameter decreases with increasing concentration of magnetic fluid and the thickness of the shell increases. The application of a magnet in the direction of the bubbles makes the magnetic shell of the bubbles thinner, which leads to further destruction of the bubbles in cases when they are covered with a shell of low-concentrated MF. In the case of bubbles covered with a shell of concentrated magnetic liquids, they do not collapse.

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