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2. Evaporation

3. •Evaporation
Evaporation is nothing but a thermal separation
process. Theoretically, evaporation means simply
vaporization from the surface of a liquid. Vaporization
of a liquid below its boiling point is called evaporation.
Thus, no boiling occurs and the rate of vaporization
depends on the diffusion of vapour through the
boundary layers above the liquid.

4. During Evaporation
• Water turns from a
liquid to a gas.
• Water moves from
rivers and lakes into
the atmosphere in
the form of water
vapor.
• Water vapor forms
clouds.
• Water changes into
solid.

6. •Factors Affecting
Evaporation
There Are 4 Factors To Affect
Evaporation.
1) Temperature
2) Surface Area
3) Humidity
4)wind Speed

7. •Temperature
It is also affected by
temperature. As the
temperature of air is increased,
its capacity to hold moisture
also increases . The rate of
evaporation increases on
increasing the temperature of
the liquid. The rate of
evaporation of a liquid can be
increased by heating it.
Hence evaporation is directly
proportional to the
temperature of evaporating
surface.
Warmer the
evaporating
surface, higher
the rate of
evaporation

8. Humidity
When the humidity of air is low , then
the rate of evaporation is high, and
water evaporates more readily.
When the humidity of air is high, then
the rate of evaporation is low, and water
evaporates very slowly .

9. Wind
Speed
Evaporation depends on the wind speed as well. When the
winds are light, a thin layer of air just above the surface gets
nearly saturated; under the circumstances the difference
between the vapour pressure between ground and air is very
small . This results in very low evaporation. On the other
hand, when the wind velocity is high, turbulence is set up in
the air. Moisture evaporated from the ground is mixed
upward and the vapour-pressure difference between the
atmosphere and the surface remains large.
Thus, the rate of evaporation is accelerated. Wherever there is
a combination of high temperature, very low relative humidity
and strong wind, the rate of evaporation is exceptionally high.

10. Surface Area
The rate of
evaporation
increases on
increasing the
surface area on the
liquid.
The rate of
evaporation can be
increased by
increasing the
surface of the liquid.

11. Evaporation Cause
Cooling?
• In an open vessel the liquid
keeps on evaporating. The
particles of liquid absorb
heat energy from the
surrounding to regain the
energy lost in the
evaporation.
• This absorption of energy from the
surroundings make the liquid cool.

12. Cooling by evaporation
• Air is blown into the
dichloromethane
liquid.
• This liquid rapidly
evaporates.
• The rapid
evaporation causes
cooling.
• Eventually the water
below the can freezes
the can to the block
of wood.

13. 1 Cooling effect of
evaporation
When we apply a
perfume/alcohol to
our body... We feel
cool.
Perfume/alcohol
evaporates easily and
takes the energy
from your body.

14. Cooling of a Deodrant on
hand
• When perfume is put
on our palm, it feels
cold because the
particles of matter
gain energy from our
surroundings or
from our palm and
evaporate at a fast
rate causing our
palm to feel cold.

15. Water kept in an earthen pot
• Water kept in an
earthen pot
becomes cool after
some time because
of the tiny holes
present in the pot,
which helps the
water to evaporate.
And due to this the
water becomes cool
in a short period of
time .

16. 2.Cooling effect of
evaporation
We can easily catch
a cold when we are
wet.
As we dry out, latent
heat is taken from
our body. If it is
windy, we can cool
down even more.

17. 3.Sweating
• When we are
hot , water is
produced by our
skin.
• As this water
evaporates it
cools our skin.

18. Drying clothes
•Evaporation of water
from wet clothing is
encouraged by:
– warming (the Sun)
– blowing air across
(wind)
– maximizing the area
exposed (hanging
from a line)