Question

why do be feel relief under a fan when we are perspiring

Answer 1

We get perspiration orsweating because our body tries to cool ourselves by releasing water (sweat) through the pores of our skin. And now when we sit under a fan ,the sweat on our body evaporates due to the air directed upon us, making our body cool.

Answer 2

because our sweat evaporates faster due the presence of fast winds and for evaporation the sweat takes the latent heat from our body and evaporates by which our body feels cool. Evaporation is faster when we sit under the fan. So we feel relief.