5 research outputs found
Evaporation of Sessile Droplets Laden with Particles and Insoluble Surfactants
We
consider the flow dynamics of a thin evaporating droplet in
the presence of an insoluble surfactant and noninteracting particles
in the bulk. On the basis of lubrication theory, we derive a set of
evolution equations for the film height, the interfacial surfactant,
and bulk particle concentrations, taking into account the dependence
of liquid viscosity on the local particle concentration. An important
ingredient of our model is that it takes into account the fact that
the surfactant adsorbed at the interface hinders evaporation. We perform
a parametric study to investigate how the presence of surfactants
affects the evaporation process as well as the flow dynamics with
and without the presence of particles in the bulk. Our numerical calculations
show that the droplet lifetime is affected significantly by the balance
between the ability of the surfactant to enhance spreading, suppressing
the effect of thermal Marangoni stresses-induced motion, and to hinder
the evaporation flux through the reduction of the effective interfacial
area of evaporation, which tend to accelerate and decelerate the evaporation
process, respectively. For particle-laden droplets and in the case
of dilute solutions, the droplet lifetime is found to be weakly dependent
on the initial particle concentration. We also show that the particle
deposition patterns are influenced strongly by the direct effect of
the surfactant on the evaporative flux; in certain cases, the “coffee-stain”
effect is enhanced significantly. A discussion of the delicate interplay
between the effects of capillary pressure and solutal and thermal
Marangoni stresses, which drive the liquid flow inside of the evaporating
droplet giving rise to the observed results, is provided herein
Evaporation of Sessile Droplets Laden with Particles and Insoluble Surfactants
We
consider the flow dynamics of a thin evaporating droplet in
the presence of an insoluble surfactant and noninteracting particles
in the bulk. On the basis of lubrication theory, we derive a set of
evolution equations for the film height, the interfacial surfactant,
and bulk particle concentrations, taking into account the dependence
of liquid viscosity on the local particle concentration. An important
ingredient of our model is that it takes into account the fact that
the surfactant adsorbed at the interface hinders evaporation. We perform
a parametric study to investigate how the presence of surfactants
affects the evaporation process as well as the flow dynamics with
and without the presence of particles in the bulk. Our numerical calculations
show that the droplet lifetime is affected significantly by the balance
between the ability of the surfactant to enhance spreading, suppressing
the effect of thermal Marangoni stresses-induced motion, and to hinder
the evaporation flux through the reduction of the effective interfacial
area of evaporation, which tend to accelerate and decelerate the evaporation
process, respectively. For particle-laden droplets and in the case
of dilute solutions, the droplet lifetime is found to be weakly dependent
on the initial particle concentration. We also show that the particle
deposition patterns are influenced strongly by the direct effect of
the surfactant on the evaporative flux; in certain cases, the “coffee-stain”
effect is enhanced significantly. A discussion of the delicate interplay
between the effects of capillary pressure and solutal and thermal
Marangoni stresses, which drive the liquid flow inside of the evaporating
droplet giving rise to the observed results, is provided herein
Возможные пути решения проблемы существования неиспользуемых участников в садоводческих товариществах Республики Беларусь
Recent experimental
results suggest that stacked layers of graphene oxide exhibit strong
selective permeability to water. To construe this observation, the
transport mechanism of water permeating through a membrane consisting
of layered graphene sheets is investigated via nonequilibrium and
equilibrium molecular dynamics simulations. The effect of sheet geometry
is studied by changing the offset between the entrance and exit slits
of the membrane. The simulation results reveal that the permeability
is not solely dominated by entrance effects; the path traversed by
water molecules has a considerable impact on the permeability. We
show that contrary to speculation in the literature, water molecules
do not pass through the membrane as a hydrogen-bonded chain; instead,
they form well-mixed fluid regions confined between the graphene sheets.
The results of the present work are used to provide guidelines for
the development of graphene and graphene oxide membranes for desalination
and solvent separation
Experimental and Theoretical Study of the Emergence of Single Chirality in Attrition-Enhanced Deracemization
Experimental studies help to deconvolute
the driving forces for
crystal growth during attrition-enhanced deracemization, demonstrating
an interplay between crystal size and crystal number in the emergence
of homochirality. A semiempirical population balance model is presented
based on considerations of the solubility driving force, as outlined
by the Gibbs–Thomson rule, and a frequency factor based on
the total interfacial surface area between solid crystals and the
solution phase
Liquid–Liquid Dispersion Performance Prediction and Uncertainty Quantification Using Recurrent Neural Networks
We demonstrate the application of a recurrent neural
network (RNN)
to perform multistep and multivariate time-series performance predictions
for stirred and static mixers as exemplars of complex multiphase systems.
We employ two network architectures in this study, fitted with either
long short-term memory and gated recurrent unit cells, which are trained
on high-fidelity, three-dimensional, computational fluid dynamics
simulations of the mixer performance, in the presence and absence
of surfactants, in terms of drop size distributions and interfacial
areas as a function of system parameters; these include physicochemical
properties, mixer geometry, and operating conditions. Our results
demonstrate that while it is possible to train RNNs with a single
fully connected layer more efficiently than with an encoder–decoder
structure, the latter is shown to be more capable of learning long-term
dynamics underlying dispersion metrics. Details of the methodology
are presented, which include data preprocessing, RNN model exploration,
and methods for model performance visualization; an ensemble-based
procedure is also introduced to provide a measure of the model uncertainty.
The workflow is designed to be generic and can be deployed to make
predictions in other industrial applications with similar time-series
data