Interfacial deformation and jetting of a magnetic fluid

TL;DR

This paper presents a numerical model that predicts the deformation and jetting behavior of a magnetic fluid under magnetic field gradients, capturing the transition from steady interface to jet formation without fitting parameters.

Contribution

The study develops a coupled Navier-Stokes and Maxwell equations model to accurately simulate magnetic fluid interface deformation and jetting phenomena.

Findings

The model predicts the critical magnet distance for jet formation.

It accurately captures large interfacial deformations.

The approach is free of fitting parameters.

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 addressed theoretically and experimentally [Soft Matter, (9) 2013, 8600-8608]: 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 any fitting parameter.