Sessile drops are usually encountered in daily life

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Introduction:
Sessile drops are usually encountered in daily life, including espresso spills, rain water drops on rain coat and water onto
a cooking plate. For hundreds of year, research has been conducted over sessile drop to study the surface and the contact
phenomenon such as evaporation, dynamics spreading, contact angle and the surface characteristics such as wettability and
surface roughness. Along the way different method were adopted for visualization and quantification of sessile drop namely
Goniometry method, Wilhelmy plate method, Captive bubble method or Axisymmetric Drop Shape Analysis.
The behavior of sessile drop in contact with various solid surfaces vary as some of the liquids wet the surface to a limited
extent forming an intermediate drop shape at a given contact angle whereas some of the liquid spreads over the solid
surfaces making a film. This behavior of sessile drop to maintain contact with solid surface is called wetting. When a
sessile drop is formed on the solid surface, the angle formed between the solid surface and a tangent aligned with the liquid
at the apparent intersection of three interface is defined as contact angle (figure 1). The three interfaces are solid-liquid,
liquid-vapor and solid-vapor interfaces. The intersection of all three interfaces is called contact line. Contact angle is the
macroscopic representation of microscopic phenomenon such as surface energies, surface roughness and also the surface
coating has the crucial role in the wettability of the material for a given liquid [1].
The problem of the evaporation of a liquid drop has been known for many years [1,2] and recently again attracted the
interest of many researchers. This problem is particularly actual in microfluidics, where evaporation plays crucial role for
the small droplet size .A drop deposited on a solid substrate forms together with solid and gas phases the triple contact line.
Understanding of evaporation and heat transfer processes in a liquid drop and near the contact line is very important for
many industrial applications such as micro-electronics, micro- and nanofabrication, ink jet printing, and other fields.
A lot of theoretical and experimental studies of the evaporating droplet with small capillary size exist in the literature. The
diffusive evaporation rates depend on contact angle [3] and the investigations of the substrate nature effect [4] still remain
an important issue. The evaporation of sessile drops of pure liquids is satisfactorily described by model of Hu and Larson
[5] based on a purely diffusive evaporation mass flux for the case of natural evaporation at ambient temperature. The recent
achievements on the topic are presented by review of Erbil [6]. However, the coupled heat and mass transfer problem when
the substrate is heated still requires more analysis and understanding. Such studies are important for understanding of the
heat transfer enhancement as well as contact line dynamics.
The evaporation of the sessile droplet on the heated surface is a common physical phenomenon encountered in
various situations and therefore, has received significant attention in the literature. On forming the sessile drop on the flat
surface, it forms wedge like shape near the contact line that creates the evaporation driven capillary flow. This capillary
flow sucks the drop to the contact line and due to the wedge shape of the evaporating droplet the evaporation rate increases
towards the wedge. The evaporation rate causes the mass-loss from the liquid phase and results in a changing drop profile;
either by a decrease in contact angle or a reduction in base radius or a blend of both. Picknett and Bexon, led a hypothetical
and trial examination concerning the evaporation of small drops where gravitational effects were neglected and a spherical
cap approximation for the drop shape analysis was applied. The outcome show the nearness of three distinct modes of drop
evaporation: constant contact radius (CCR), constant contact angle (CCA) or a mixed mode (Picknett and Bexon 1997). A
couple of years after the turning point work of Picknett and Bexon the evaporation modes were accounted to the wetting
behaviour by Birdi et al.. On hydrophilic surfaces, as the evaporation begin the contact angle decreases in time and the
contact radius remains constant (Birdi et al., 1989). The aim of this project is to analyse the spreading behaviour of several
liquids on aluminium surface with different roughness and to analyse the evaporation pattern of the sessile drop formed on
the solid surface.
1.1 Brief description of p…

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Original essay on: Sessile drops are usually encountered in daily life

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Introduction:Sessile drops are usually encountered in daily life, including espresso spills, rain water drops on rain coat and water onto
a cooking plate. For hundreds of year, research has been conducted over sessile drop to study the surface and the contact
phenomenon such as evaporation, dynamics spreading, contact angle and the surface characteristics such as wettability and
surface roughness. Along the way different method were adopted for visualization and quantification of sessile drop namely
Goniometry method, Wilhelmy plate method, Captive bubble method or Axisymmetric Drop Shape Analysis.
The behavior of sessile drop in contact with various solid surfaces vary as some of the liquids wet the surface to a limited
extent forming an intermediate drop shape at a given contact angle whereas some of the liquid spreads over the solid
surfaces making a film. This behavior of sessile drop to maintain contact with solid surface is called wetting. When a
sessile drop is formed on the solid surface, the angle formed between the solid surface and a tangent aligned with the liquid
at the apparent intersection of three interface is defined as contact angle (figure 1). The three interfaces are solid-liquid,
liquid-vapor and solid-vapor interfaces. The intersection of all three interfaces is called contact line. Contact angle is the
macroscopic representation of microscopic phenomenon such as surface energies, surface roughness and also the surface
coating has the crucial role in the wettability of the material for a given liquid [1].
The problem of the evaporation of a liquid drop has been known for many years [1,2] and recently again attracted the
interest of many researchers. This problem is particularly actual in microfluidics, where evaporation plays crucial role for
the small droplet size .A drop deposited on a solid substrate forms together with solid and gas phases the triple contact line.
Understanding of evaporation and heat transfer processes in a liquid drop and near the contact line is very important for
many industrial applications such as micro-electronics, micro- and nanofabrication, ink jet printing, and other fields.
A lot of theoretical and experimental studies of the evaporating droplet with small capillary size exist in the literature. The
diffusive evaporation rates depend on contact angle [3] and the investigations of the substrate nature effect [4] still remain
an important issue. The evaporation of sessile drops of pure liquids is satisfactorily described by model of Hu and Larson
[5] based on a purely diffusive evaporation mass flux for the case of natural evaporation at ambient temperature. The recent
achievements on the topic are presented by review of Erbil [6]. However, the coupled heat and mass transfer problem when
the substrate is heated still requires more analysis and understanding. Such studies are important for understanding of the
heat transfer enhancement as well as contact line dynamics.
The evaporation of the sessile droplet on the heated surface is a common physical phenomenon encountered in
various situations and therefore, has received significant attention in the literature. On forming the sessile drop on the flat
surface, it forms wedge like shape near the contact line that creates the evaporation driven capillary flow. This capillary
flow sucks the drop to the contact line and due to the wedge shape of the evaporating droplet the evaporation rate increases
towards the wedge. The evaporation rate causes the mass-loss from the liquid phase and results in a changing drop profile;
either by a decrease in contact angle or a reduction in base radius or a blend of both. Picknett and Bexon, led a hypothetical
and trial examination concerning the evaporation of small drops where gravitational effects were neglected and a spherical
cap approximation for the drop shape analysis was applied. The outcome show the nearness of three distinct modes of drop
evaporation: constant contact radius (CCR), constant contact angle (CCA) or a mixed mode (Picknett and Bexon 1997). A
couple of years after the turning point work of Picknett and Bexon the evaporation modes were accounted to the wetting
behaviour by Birdi et al.. On hydrophilic surfaces, as the evaporation begin the contact angle decreases in time and the
contact radius remains constant (Birdi et al., 1989). The aim of this project is to analyse the spreading behaviour of several
liquids on aluminium surface with different roughness and to analyse the evaporation pattern of the sessile drop formed on
the solid surface.1.1 Brief description of previous research on contact angle measurement<span class="font…

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