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Numerical Heat Transfer, Part A: Applications
An International Journal of Computation and Methodology
Volume 70, 2016 - Issue 10
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Original Articles

Internal fluidity of a sessile droplet with the presence of particles on a hydrophobic surface

, , &
Pages 1118-1140 | Received 01 May 2016, Accepted 09 Aug 2016, Published online: 20 Oct 2016
 

ABSTRACT

Thermocapillary flow inside a sessile droplet is considered in relation to microsized particles, resembling the environmental dust particles’ removal from the hydrophobic surface. Polycarbonate surface is textured through solution-induced crystallization to generate surfaces with hydrophobic characteristics. The dusts are collected from the local environment and characterized using the analytical tools. Internal fluidity of the droplet is simulated numerically in line with the experimental conditions. An experiment is carried out to measure the velocity of the dust particles using the optical microscopic system. It is found that thermocapillary-induced forces generate counter-rotating cells in the droplet, which depends on the droplet contact angle. The percentage of dust particles removed from the hydrophobic surface into the droplet, due to droplet internal fluidity, increases with the size of the dust particles and it remains almost constant with progressing time. The dust particles follow the streamlines in the circulation cells inside the droplet.

Nomenclature

Bo=

Bond number

Cp=

specific heat capacity

g=

gravity

Gr=

Grasshoff number

k=

thermal conductivity

Ma=

Marangoni number

Nu=

Nusselt number

p=

pressure

R=

the wetting radius

T=

temperature

t=

time

V=

velocity

=

volume of the droplet

β=

thermal expansion coefficient

=

temperature derivative of the surface tension

μ=

dynamic viscosity

ν=

kinematic viscosity

ρ=

density

σ=

surface tension

θ=

contact angle

Subscripts=
D=

drag

eff=

effective

ext=

external

g=

gravity

P=

particle

W=

water

o=

refer to ambient

Nomenclature

Bo=

Bond number

Cp=

specific heat capacity

g=

gravity

Gr=

Grasshoff number

k=

thermal conductivity

Ma=

Marangoni number

Nu=

Nusselt number

p=

pressure

R=

the wetting radius

T=

temperature

t=

time

V=

velocity

=

volume of the droplet

β=

thermal expansion coefficient

=

temperature derivative of the surface tension

μ=

dynamic viscosity

ν=

kinematic viscosity

ρ=

density

σ=

surface tension

θ=

contact angle

Subscripts=
D=

drag

eff=

effective

ext=

external

g=

gravity

P=

particle

W=

water

o=

refer to ambient

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