Why is the water in the earthen pot cool?

The earthen pot contains small pores. The water tries to go out through this holes but it gets evaporates on the outer surface of the pot. For the water to change from its liquid to vapour state it needs energy. This energy is taken from the remaining water inside the earthen pot as heat energy. So the water inside the earthen pot gets cooled.

Science Jul 22, 2019 0 8881 Add to Reading List

Why is the water in the earthen pot cool?

Short Answer:

The earthen pot contains small pores. The water tries to go out through this holes but it gets evaporates on the outer surface of the pot. For the water to change from its liquid to vapour state it needs energy. This energy is taken from the remaining water inside the earthen pot as heat energy. So the water inside the earthen pot gets cooled.

If you don’t understand keep reading.

Cooling of water:

Water can be cooled in two ways:

1. Normally heat will flow from hot body to cold body.

$Description: C:\Users\Manova\Desktop\blogs\blog7\body.png$

So to cool water which is in a container we need to make the outer surrounding cooler than the water. So the water will be cooled. For instance we use refrigerator to cool the water.

$Description: C:\Users\Manova\Desktop\blogs\blog7\fridge.png$

2. Water which is direct contact with the air evaporates. For the water to evaporate from liquid to vapour it needs heat energy. This energy is taken from the remaining water and the water is cooled.

$Description: C:\Users\Manova\Desktop\blogs\blog7\pot.png$

Why is the water in the glass or plastic bottles not cool?

If you take the glass or bottle there is no any pores and so evaporation will not happen on through the walls. But on the top surface evaporation will happen if it is not closed. But the heat will again flow from surrounding air to the glass or bottle through the wall. In the case of the pot, the wall won’t allow the heat transfer inside or outside much like thermo Cole.

Glass, Plastic → Heat transfer rate is high.

Earthen pot, Thermo Cole → Heat transfer rate is low.

$Description: C:\Users\Manova\Desktop\blogs\blog7\compare.png$

Some Facts:

1) Why dogs are keeping their tongue outside in summer season or in the time of hot?

Some of the spit from the dog gets evaporates and it takes the heat from the dog’s tongue to evaporate. So the tongue and the surrounding area get cooled. The dog feels cool.

2) Why do the human beings feel comfort in front of the fan even they get more sweat?

When the human being is exposed to the air of the fan the sweat from the body evaporates and it takes the heat from the man’s skin to evaporate. So the skin and the body get cooled. He feels cool and comfortable.

3) Why is the water in the lake or the river or the pond cooler than the atmospheric air surrounding it?

The little amount of water in the surface of the lake or the river or the pond gets evaporated and it takes the heat from the surrounding water for the evaporation process to happen. So the surrounding or remaining water gets cooled. Thus the water is cooler than the atmospheric air surrounding it.

Then comes the question, why then I have studied in the school that water boils at 100 degree Celsius at 1 atm. Yes, it is true. But it is boiling not evaporation.

Boiling:

$Description: C:\Users\Manova\Desktop\blogs\blog7\boiling.png$

In boiling the water forms the bubbles and becomes vapour at the surface of the vessel and goes out of the vessel.

a. Here heat transfer occurs between the surface of the vessel (Solid) and the liquid.

Solid – Liquid interface with bubble formation

b. But in the case of evaporation heat transfer occurs between the liquid and vapour.

Liquid - Vapour interface without bubble formation