Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
Controlling the relaxation and breakup of initially elongated ferrofluid droplets with rotating magnetic fields
Submission Author:
Arthur Guilherme , PB
Co-Authors:
Arthur Guilherme, Taygoara Oliveira
Presenter: Arthur Guilherme
doi://10.26678/ABCM.COBEM2023.COB2023-1993
Abstract
The relaxation and breakup of an elongated superparamagnetic ferrofluid droplet immersed in a nonmagnetic viscous fluid subjected to static and rotating uniform magnetic fields are considered by using a multiphase numerical model. Both phases are immiscible and incompressible fluids with equal density and viscosity. The relaxation follows the abrupt termination of a planar extensional flow, which, in turn, determines the droplet’s initial shape. The relaxation of initially elongated regular viscous droplets has been studied in the last decades, giving rise to important contributions in areas such as microfluidics, food processing, and pharmaceuticals. However, to the best of our knowledge, studies of initially elongated magnetic responsive droplets under the influence of magnetic fields during the relaxation process have not been published yet. The present study focuses on how the magnetic field, together with the capillary relaxation, affects the breakup pattern of initially elongated ferrofluid droplets. The magnetic capillary number, which measures the ratio between magnetic stress and surface tension, the dimensionless rotational frequency of the magnetic field (zero for static field), the initial magnetic field direction, and the axis of rotation are the key parameters considered in the analysis. The full incompressible Navier-Stokes equations with capillary and magnetic source terms are solved using the classical projection method in a staggered grid, while the interface capturing problem is treated using a level-set method with conservative high-order time and space discretization. The validity of the method is confirmed by comparing the results for a regular droplet with previous numerical and experimental data. We present results comparing the relaxation pattern for different magnetic field rotational frequencies and directions of rotation. The simulation results reveal that the application of rotating magnetic fields can control the relaxation and breakup pattern of the droplets, altering the number and volume ratio of resulting daughter droplets by simply varying the rotational frequency. We also observed that rotating magnetic fields can induce breakup even when the droplet is initially elongated by the action of a magnetic field, eliminating the need for flow. These findings provide insights into new methods for controlling droplet breakup in microfluidic applications and magnetic emulsion formation.
Keywords
Droplet relaxation, Magnetic-induced breakup, Rotating field, Breakup control
