How does water kept in an earthen pot become cool during summer?

Insulation

First, you should realize that there is nothing magical about earthenware or ceramic materials. The pot material does not decrease or increase the temperature of its contents, but it does insulate it somewhat from the temperature of the air around the pot.

If you pour cold water into an earthenware pot, jug, or ewer that has been kept indoors at room temperatures, the temperature of the water will increase to match the temperature of the inside of the vessel. This is true whether you store the jug inside or bring it outside into the heat. This is mainly due to the fact that the material acts as a good insulator and doesn't conduct heat well, so heat (thermal energy) cannot flow from the air surrounding the jug to the water inside it.

Note that had you placed hot water in the earthenware jug, it would remain hot longer than if you placed it in a container made of some material that doesn't insulate. So the earthenware jug keeps the hot stuff hot and the cold stuff cold. That's what a modern thermos does.

Evaporative Cooling

I actually think there is more too it than only insulation. Assuming the earthenware pot absorbs some of the water in it (which it will if it is not sealed with a glaze or other coating), then the outside of the pot will be slightly moistened. As this moisture on the pot evaporates, the temperature of the pot is reduced due to evaporative cooling (same way sweat cools the body). This cooling effect will keep the temperature of the pot lower then it would otherwise be. This effect will only work as long as the outside of the pot is kept moist.

Actual Phenomenon

Evaporate cooling! It's Half correct. Let me finish it.

Material: Burnt Clay

Clay itself is a mixture of water and mud i.e., what we mould to make a pot. After that the wet clay pot is heated so that all the moisture in the wet clay is taken out completely. But who is going to fill the place of the moisture?? Nothing. So that whole material is purely porous with a very fine holes all over.

Now when u pour water of any temperature more than the room temperature into the pot.. The water first spreads itself on to the walls of the pot. Due to the internal pressure of water, the water is forced to contact to the pot inner walls.(Don't get confused. This happens with any fluid or material, generally for solids its called as angle of repose, but for fluids, the angle of repose is 180 deg, i.e., horizontal force in all directions). So the water molecules starts filling the air gaps of the pot. In this condition, due to the very fine holes, the water molecules loose their contact and forms in to separate groups of water particles. Since the water volume is very less, it tends to go away from the pothole, and for that is has to be converted in to vapor state. But the temperature of the water is not enough to change its state from liquid to gaseous. So remember that the water is still in contact with the pot, so the heat is taken from the pot shell, thus reaches its latent heat and changes it state from liquid to gaseous.

This is why the pot first cools rather to the water inside. In addition, this is a pure Heat and Mass Transfer subject. This is how the pot shell takes out the heat of the water and the immmprisoned water molecules in the pot shell take that heat out and becomes vapor.

If you can observe a pot with water for a while, check for the following points.,

1) The Whole Pot Gets Wet in outside till the level of water.

2) If you can feel the water getting cooled after an observation of 30 mins., then check for the water level in the pot. (It surely goes down and where does that water go ??)

3) Check the Pot Shell inner face temperature and water temperature, and find out which is lesser.

Anywayz.... Buzz me for any queries; I am always ready to spread knowledge.

First answer by Schnazola. Last edit by ReverseGoal. Contributor trust: 0 [recommend contributor]. Question popularity: 16 [recommend question]