Banca de DEFESA: Victor Hugo Suarez Solis

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Victor Hugo Suarez Solis
DATE: 16/12/2022
TIME: 14:30
LOCAL: Plataforma Microsoft Teams
TITLE:

An Investigation of the Microstructure and Rheology of Suspensions with NaCl Crystalline Structures in the Presence of Shear and Magnetic Field

KEY WORDS:

Magnetic Field; NaCl microcrystals Suspension; Recrystallization; MagnetoViscous effect; Pseudoplasticity; Stress Relaxation.

PAGES: 110
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

In this work, the rheological effects of applying an external magnetic field to a suspension composed of NaCl crystals dispersed on an aqueous supersaturated solution of the same salt are studied using experimental protocols of the Laboratory of Microhydrodynamics and Rheology of the University of Brasília. The device used in the experiments is a parallel disk rheometer equipped with a magnetic cell. Static tests at constant temperature are performed in the absence of flow. Crystals grow in the solution because salt molecules meet up and interlock, arranging themselves in a lattice structure. These tests indicate, by microscopy observation, that the mean length of the crystals’ microstructure after recrystallization is greater the more intense the magnetic field applied to the samples is. By rheometric experiments (flow regime), we evaluated the behavior of the suspension viscosity in a weak flow regime at a controlled temperature for six increasingly higher magnetic field intensities. These tests show that the suspension viscosity decreases in a nonlinear fashion as the magnetic field intensity increases. This behavior is understood as a result of a weakening of the bonds in the crystal structures, which makes them more susceptible to breakups under the action of a shearing flow. The suspensions present a shear-thinning for every applied magnetic field, which is well described by a power-law model. Experiments in the regime of small amplitude oscillatory shear are also carried out. The viscoelastic modules are determined and we find that the storage modulus does not vanish at low frequencies, indicating the existence of a shear elastic modulus at equilibrium. Experiments using a step-strain in the presence of a magnetic field were also conducted. The stress relaxation function as a function of the magnetic field was obtained and a spectrum of relaxation times determined, showing complex memories of the examined suspensions with three relaxation times. The stress is found to relax to a residual stress, which decreases as the intensity of the applied magnetic field is increased. The results of this work can all be related to changes in the growth rate distribution and size distribution of the salt crystals with the intensity of an applied magnetic field. The present study could be important in the applications involving treatments of kidney stone formation by monitoring an external magnetic field.

BANKING MEMBERS:
Externo ao Programa - 3087995 - ANDRE VON BORRIES LOPES
Externo à Instituição - ERICK DE MORAES FRANKLIN
Presidente - 1170729 - FRANCISCO RICARDO DA CUNHA
Interno - 2730343 - RAFAEL GABLER GONTIJO