Rate of Evaporation
- Evaporation is the process of converting a substance (such as water) from its liquid state to its gaseous state at temperature lower than the boiling point of the liquid.
- There are several ways of making a liquid evaporate faster:
- Increase its temperature
- Increase its surface area
- Pass air through it or across its surface
- Make the liquid into a fine spray
A spray is made up of millions of tiny liquid droplets with a very large total surface area. The highly curved surfaces make it easier for molecules to escape.
Cooling by Evaporation
- Blowing air into a liquid will cause the liquid evaporate faster.
- During evaporation, latent heat is absorbed from the liquid (as a surrounding) causing the temperature of the liquid decreases.
Applications of Cooling by Evaporation
- The cooling effect in many refrigerators is produced by the evaporation of a volatile liquid called Freon.
- The liquid Freon evaporates rapidly in the pipes in the freezer compartment as more and more of its vapour is drawn away by the electric pump. As the Freon evaporates, it draws the necessary latent heat from the food inside the refrigerator.
- The pump compresses the vapour which turns liquid again on being forced through the zig-zag pipe at the back of the refrigerator. The latent heat released is given off through the cooling fins.
- In this way, thermal energy is extracted from the food inside the refrigerator and given out at the back. A refrigerator actually makes your kitchen warmer.