Evaporation of water absorbs heat energy from the surroundings. The full explanation is out of syllabus but for those interested, you can read up on latent heat and enthalpy of vaporization. Similarly, melting of ice also absorbs heat energy.
From past year’s PSLE:
Some buildings use a cooling mist system 2 lower the temperature of the surrounding air. the mist comes out in the form of small water droplets.
Q: How does the cooling mist system help 2 lower the temp of the surrounding air? (2m)
Some fans were added 2 the cooling mist system.
Q: how do the fans help in the cooling mist system? (1m)
Evaporation of the water droplets absorbs heat energy. The heat from the surrounding air is lost to the evaporating water and this lowers the temperature of the surrounding air. Mist increases the surface area of the water droplets, so that there is a greater rate of evaporation.
The use of fans creates wind which further increases the rate of evaporation and produces a greater cooling effect. It also disperses the mist and the cooler air, circulating the air which increases the efficiency of the cooling.