Biomedical Engineering Reference
In-Depth Information
are actually intimately related to the multiphase character of evaporating systems
and to the fundamental constraint to numerically catch free evolving interfaces.
The issue of free interfaces tracking motivated more than two decades of research
activity and still remains one of the most challenging field in CFD. In this context, it
appears that the coupling of Eulerian approaches together with Level Set techniques
are the most promising for robust and CPU effective multiphase simulations. For
evaporating droplets on heated substrates, such an approach would present the great
interest to allow the treatment of the solid substrate, the evaporating liquid and the
surrounding gas on the same basis without the necessity to invoke quasi-steadiness
hypotheses or spherical cap geometries.
F.
C o n c l u s i o n
The evaporation and wetting of sessile droplets is a growing area of interest to scien-
tists and engineering. This increasing interest is driven by many recent applications
making use of this fundamental phenomenon. With these exciting opportunities
there are some serious challenges concerning the understanding of underlying phys-
ical mechanisms. In studying this phenomenon two main approaches have been
adopted over the last decade, experimental techniques and numerical modeling ap-
proaches. A variety of experimental techniques have been utilized to reveal the
trends and behavior associated with phase changes and wetting of sessile droplets,
whether on heated substrates or evaporating under ambient conditions. To measure
evaporation rates and droplet profile evolution, some of the experimental techniques
used include optical measurements, microbalances and Atomic Force Microscopes
cantilevers. To measure interfacial and bulk temperatures, microthermocouples and
infra red thermography have been implemented. The hydrodynamics within evapo-
rating droplets has also been characterized using Particle Image Velocimetry (PIV)
techniques. The use of these experimental techniques by numerous research groups
over the last decade has led to the establishment of some accepted trends and behav-
iors regarding the evaporation rates, wetting tendencies and hydrodynamics within
volatile droplets. Following these established physical trends, the challenge has
been to develop adequate theoretical models and numerical schemes to predict and
confirm experimental observations. Many numerical approaches have been devel-
oped and tested by confronting the predicted results to the experimental data with
some mixed success.
In this chapter we have reviewed some of the modeling approaches developed
to describe droplet evaporation. We pointed to the challenges posed when it gets
to developing accurate numerical approaches. Coping with free moving interfaces
and being able to integrate this dynamics numerically in an accurate manner is one
of these challenges. Contact lines and physical length scales in this region where
the three phase meet is another important challenge to properly model the problem.
The physical phenomena near the contact line span over length scales ranging from
continuum to molecular scales. This poses a very serious challenge to any numerical
Search WWH ::




Custom Search