how evaporation causes cooling effect....?????

When a liquid evaporates it needs to acquire potential energy to change from a liquid to a gas.
This is stored as heat.
This heat does not create a rise in temperature.
This heat is known as latent heat.
Usually you heat a kettle and the water boils.
This is putting potential energy into the water, it then boils.
When water evaporates , it takes heat from its surroundings to do so.
The effect of taking heat out of the surroundings is that the surroundings cool down.
Therefore evaporation has a cooling effect on things.

  In the case of evaporation,as it is a surface process and can take place at any temperature,(where heat is not supplied from outside genrally),the latent heat of evaporation is taken from the liquid itself and in the course of the process,the liquid loses its temperature or cooling takes place in the liquid.That means,by evaporation,cooling can take place in the liquid itself until saturation has been arrived,when no further cooling can take place.Actually this principle is used in getting the wet bulb temperature.This is explained further below.
Whenever a change of state is taking place from liquid to a gaseous,it is really a process towards a higher state,and therefore,the particles taking part in the process require some energy in the form of heat while undergoing this physical change.This heat,known as latent heat is generally supplied by the liquid only,resulting in a lowering of its own temperature.Thus evaporation causes cooling.

 Evaporation is one of the four principal ways that heat can be transferred (the other three are radiation, convection, and conduction). Evaporation of sweat from the skin is an endothermic reaction: the reaction essentially "consumes" heat, which cools the body in the process.

For a liquid to turn into gas, either by boiling or evaporation, energy is required. This is known as the latent heat of vapourisation. In the case of boiling this is provided by external heat sources but in the case of evaporation it has to come from within the liquid itself, thus cooling it.

The energy is required to break the strong bonds between the molecules in the liquid and allow them to break free in gaseous form.
Evaporation is an endothermic (heat-absorbing) process because molecules must be supplied with energy to overcome the intermolecular forces. 

Evaporation occurs at the surface of a liquid, and energy is required to release the molecules from the liquid into the gas. The use of this energy, known as latent heat, causes the temperature of the liquid to fall.

whooph what a question and scary answers

show with a help of example rate of evaporation can be increase by increasing surface area

who was the king ruled french during french revolution

louis 16

yes.In an open vessel,the liquid keeps on evaporating.The particles of liquid absorb energy from surronding to regain the energy lost during evaporation.This absorption of energy from the surrondings make the surrondings cold.