CHARACTERIZATION OF NON-EQUILIBRIUMFLUCTUATIONS DURING FREE-DIFFUSION INHIGHLY-STRATIFIED SOLUTIONS OF GLYCEROL ANDWATER
Tesi di Dottorato
Data di Pubblicazione:
2023
Citazione:
CHARACTERIZATION OF NON-EQUILIBRIUMFLUCTUATIONS DURING FREE-DIFFUSION INHIGHLY-STRATIFIED SOLUTIONS OF GLYCEROL ANDWATER / S. Castellini ; supervisore: A. Vailati ; tutor: Marina Carpineti ; coordinator: M. Paris. Dipartimento di Fisica Aldo Pontremoli, 2023 Jul 25. 35. ciclo, Anno Accademico 2022.
Abstract:
We present two topics, both in the area of transport mechanisms
(mass diffusion or heat transport) occurring in fluids. The first and
main topic is a study of the non equilibrium fluctuations (NEF) that
occur during isothermal free diffusion between two solutions of
glycerol and water with various concentration differences. The
nonlinearity of the system, determined by the strong stratification of
the sample, requires the introduction of an interpretive model
capable of characterizing the dependence of the correlation
properties of the non-equilibrium fluctuations on the local
thermophysical variables of the system. The proposed model makes
it possible to characterize the dynamics of non-equilibrium
fluctuations in the presence of a wide range of relaxation times
determined by the strong stratification of the sample, unlike the
cumulative methods commonly used in dynamic light scattering
experiments, which work well in the presence of moderate dispersion
of relaxation times. The second topic concerns the convective
structures that appear in a thermophilic suspension of nanoparticles
heated from below. Such a system presents a complex stability
diagram, determined by the competition between the stabilizing flow
of nanoparticles induced by thermophoresis and the destabilizing
flow determined by thermal convection. We analyzed Rayleigh-
Bénard convection in a suspension of highly thermophilic
nanoparticles with a large negative separation ratio Ψ = −3.5 heated
from below. We demonstrated the presence of transient states
localized in the range of Rayleigh numbers 2200 < Ra < 3000. These
states rotate rapidly around their axis and gradually decrease in size
until the system returns to a purely conductive state. This second
topic is not totally separate from the first one, since the study of the
stability diagram is the first step toward studying the thermal and
concentration fluctuations generated by heating a thermophilic
colloidal suspension from below.
Tipologia IRIS:
Tesi di dottorato
Keywords:
Non Equilibrium Fluctuations; Diffusion; Glycerol; Solutions; Water
Elenco autori:
S. Castellini
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