Why (or how) sprinkling reduces the temperature of the liquid ?

Question

This principle is used in fire fighting machines viz.sprinkler.
This we experience in day-to-day life also.Water from Shower is cooler than tap water. How? What is the physics/science behind it?

Answer 1

Actually it is the air surrounding the water spray that turns cooler.

If the relative humidity is low, and water is misted into that dry air, some of it will evaporate. In the process of evaporating water from the surface of the droplets (or stream of drops), heat from the air molecules is transferred to the water to vaporize it (you can look up the "heat of vaporization" to find out how much). So, as the heat is transferred from the air to the water, the air gets cooler and more saturated with water vapor.

This is the principle of how evaporative ("swamp") coolers work -- like the one at my house.

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Answer 2

Fire-fighting uses sprinkling not because it cools the water, but because it increases the surface area covered. 100 degree water will be just as effective as 40 degree water at snuffing out a flame by depriving it of oxygen (not by cooling it). Shower water is also not cooler than tap water. Unless the air is significantly colder than the tap water (in which case you shouldn't be showering), it's just the fact that your skin loses more heat when wet than the inside of your mouth does (you lose 70% of your body heat thru your scalp). Try putting a glass under the showerhead and comparing it to a glass of tap water. They will be the same temperature.

Answer 3

you are correct, because sprinkling increases the rate of evaportation. the molecules in a liquid do not all move at the same speed, temperature is a bulk measure of the average molecular velocity (higher speed = higher temp at the molecular level). to evaporate the molecule has to be at the equivalent of 212 degrees, so evaporation selectively removes the highest moving molecules only from the liquid. with the loss of the most energetic molecules, the bulk temperature of the remaining liquid lowers. people have used this principle to advantage in desert climes with lister bags. the exterior of the bag promotes evaporation which allows the remaining liquid to become cooler than the surrounding air temperature.

i don't think your examples are representative of the cooling effect, but you basic premise, that sprinkling reduces liquid temperature is correct.

Answer 4

Several good answers. That effect you mention is called evaporative cooling. There are many applications of it, and designing equipment to do that is a science.

Answer 5

Let me make a guess. If you split something up, whether it be water or something else, you are increasing the surface area available for exposure to the ambient.