Nonlocal-nonlinear dynamics in core-annular ferrofluid systems

Source abstract

Abstract A weakly nonlinear analysis is conducted on a two-ferrofluid system in a rod-annular geometry, where a thin ferrofluid film coats a current-carrying wire, and a second ferrofluid of different magnetic susceptibility fills the region between the film and the annulus. An azimuthal field generated by the current and an applied axial field produce a magnetic forcing, interacting with surface tension at the interface of the fluids. A nonlocal PDE is derived, governing the interface evolution of the initially stationary system, where numerical solutions reveal the complexity of the interplay between the magnetic and capillary forcing. The magnetic field can further enhance the development of lobe and collar structures, features that arise in the hydrodynamic case, thereby increasing the surface area of the interface. Under certain settings, it can provide partial stabilisation and even a flat stable interface. The interface morphology is readily influenced by the field strengths, the domain size, and the radius of the annulus, offering precise control over interfacial profiles and surface area. Such manipulability may have important implications for applications in coating, printing, heat transfer, and microfluidic transport.