N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

Analysis of the Evaporation of Water Droplets from Textured

Surfaces

Neil Shirtcliffe, Sanaa, Aqil, Glen McHale, Michael Newton and Y. Erbil

Lei Zhai et. Al.

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

NormalWenzel, total contact

sr r θθ coscos =

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

NormalCassie-BaxterPartial contact

( )11 1 fCosfCos sr −−= θθ

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

Richard Burkmar 2004 Rosemary Calvert

Ken Love

Ken Love

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

θθθθ

θθθθ

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

cDRdt

dVS

CL ∆−= πρ 4

( )θπρ cfDRdt

dVS

CL ∆−= 4

( ) ( )oPBbL

ePB Hr

ctDueueue

u

eH θ

ρθ +∆−=++++

+−≡

22

3210 2)1(log

1

Spherical drop in free space

Picknett and Bexon, drop on a surface

Approximation for 90 to 180°

cD∆u(t)=cosθ(t)

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

0

30

60

90

120

150

180

0 200 400 600 800 1000 1200 14000.0

0.3

0.6

0.9

1.2

1.5

1.8

Time, s

Con

tact

Ang

le,

θθ θθo

Diam

eter or H

eigh

t, mm

1 2 3

d

h

θ

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

For Stage 1 it is possible to model the evaporation with a constant contact radius, 2, 3.

( )L

LV cfD

dt

dA

ρθπ ∆−=

8

3

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

0 100 200 300 400 500 600 700 800

Time/s

A/m

m2

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

0.0

1.5

3.0

4.5

6.0

7.5

9.0

0 400 800 1200 1600 2000

Time, s

D∆∆ ∆∆

ct+k

, x10

-4 k

g m

-1

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

130.0

130.5

131.0

131.5

132.0

132.5

133.0

1800 2000 2200 2400 2600 2800 3000 3200

0.6

0.7

0.8

0.9

1.0

1.1

1.2

Time, s

Con

tact

Ang

le,

θθ θθo

Diam

eter or H

eigh

t, mm

Stage 2

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

∆+−=∆b

b

r

r)cos2(sin θθθ

θθ

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

d)c)a) b)

e) f) g) h)

Drop Collapse

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

0

30

60

90

120

150

180

0 200 400 600 800 1000 1200 1400

0.0

0.3

0.6

0.9

1.2

1.5

1.8

Time, s

Con

tact

Ang

le,

qo

Diam

eter or H

eig

ht, m

m

N. Shirtcliffe G. McHale

M. Newton S. Aqil Y. Erbil

Values of D calculated using two different approxim ations are very close to literature values, the cooling ef fect of the drop drying could not be calculated.

The Drying followed the predicted pattern initially

Despite this drops on Super-hydrophobic surfaces la st longer (on leaves the volume is increased by collec ting water over the whole surface).