Banca de DEFESA: Arthur Leite Guilherme

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Arthur Leite Guilherme
DATE: 07/08/2023
TIME: 14:00
LOCAL: Plataforma Microsoft Teams
TITLE:

EXTENSIONAL RHEOLOGY AND MAGNETIZATION OF DILUTE FERROFLUID EMULSIONS

KEY WORDS:

Ferrofluid droplet, Extensional rheology, Emulsion magnetization,
Drop rupture

PAGES: 85
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

This work presents an investigation of the effects of external uniform magnetic fields on the
rheology and magnetization of dilute ferrofluid emulsions subjected to planar extensional
flows. To this end, we performed three-dimensional numerical simulations of a single
superparamagnetic ferrofluid droplet suspended in a nonmagnetizable viscous fluid. This
system corresponds to the emulsion’s microstructural unit. The full incompressible
Navier-Stokes equations for a biphase system with the addition of the magnetic term are
solved using a projection method. The interface problem is addressed with the Level-Set
method. We find that the droplet’s configuration and magnetization depend on the external
field intensity and direction. Macroscopically, the droplet contribution to the bulk stress state
is anisotropic. The two extensional viscosities associated with the normal stresses of the
emulsion either remain constant or increase with the field intensity; the only exception occurs
when the field direction is perpendicular to the extension plane, in which the second
extensional viscosity decreases. When the external field is not aligned with the flow main
directions, the droplet tilts in the flow and the droplet magnetization points no longer in the
external field direction. At the emulsion level, this results in internal torques that lead to a
nonsymmetric stress tensor. In order to account for the unexpected shear components and
fully characterize the extensional rheology, we introduce new extensional material functions
such as shear and rotational viscosity coefficients. We also analyze the conditions for droplet
breakup. We find that the external field either induces or prevents the breakup depending on
the field direction. The subcritical deformations in the plane formed by the extension and
field directions vary linearly with the critical extension rate, regardless of the field direction.
Overall, this study provides new insights into applications for field-controlled smart materials
and precise manipulation of ferrofluid droplets.

COMMITTEE MEMBERS:
Interno - 2245668 - MARIO BENJAMIM BAPTISTA DE SIQUEIRA
Externo à Instituição - RONEY LEON THOMPSON - UFRJ
Presidente - 3375759 - TAYGOARA FELAMINGO DE OLIVEIRA
Externo ao Programa - 1700664 - YURI DUMARESQ SOBRAL - null