Question

Why does a desert cooler cool better than a ceiling fan on a hot dry day ?

Answer 1

Fans essentially circulates the air around it rather than create a cooling effect. On a hot dry day, it circulates the hot air around it and dissipates the heat in the room but doesn't cause cooling. During hot dry day, rate of evaporation increases, hence cooling effect increases. Therefore desert coolers cool better than a ceiling fan on a hot dry day.

Answer 2

The particles of liquid in desert cooler absorb energy from the surrounding to regain the energy lost during evaporation. In summer this is fast. Hence desert cooler cool better in a hot dry day.