Interfacial deformation and jetting of a magnetic fluid. (2nd January 2016)

• Record Type: Journal Article
• Authors: Afkhami, Shahriar; Cummings, Linda J.; Griffiths, Ian M.
• Is Part Of: Computers & fluids. Volume 124(2016)
• Page Start: 149
• Page End: 156
• Publication Date: 2016-01-02
• Subjects: Moving boundaries and interfaces -- Navier–Stokes solver -- Maxwell equations -- Magnetic fluids -- Volume of fluid method; Fluid dynamics -- Data processing -- Periodicals; 532.050285
• DOI: 10.1016/j.compfluid.2015.05.015
• Languages: English
• ISSNs: 0045-7930

Abstract

Highlights: We model nonlinear evolution of ferrofluid–air interface under a magnetic field. We determine interfacial deflection of a magnetic fluid and transition into a jet. Numerical results provide data of maximum deflection of a ferrofluid. A scaling law, without a free parameter, for maximum deflection is predicted. Abstract: An attractive technique for forming and collecting aggregates of magnetic material at a liquid–air interface by an applied magnetic field gradient was recently proposed, and its underlying principle was studied theoretically and experimentally (Tsai et al., 2013): when the magnetic field is weak, the deflection of the liquid–air interface has a steady shape, while for sufficiently strong fields, the interface destabilizes and forms a jet that extracts magnetic material. Motivated by this work, we develop a numerical model for the closely related problem of solving two-phase Navier–Stokes equations coupled with the static Maxwell equations. We computationally model the forces generated by a magnetic field gradient produced by a permanent magnet and so determine the interfacial deflection of a magnetic fluid (a pure ferrofluid system) and the transition into a jet. We analyze the shape of the liquid–air interface during the deformation stage and the critical magnet distance for which the static interface transitions into a jet. We draw conclusions on the ability of our numerical model to predict the large interfacial deformation and the consequent jetting, free of fitting parameters.