This question already has an answer here:
I hope the question is clear enough and I'm sure that you can try this thing quite easily yourself. When I blow air from my mouth to my palm through a small opening, I feel cool in my palm, but its very warm when I do the same with an open mouth!
Does it have something to do with the speed at which the air is moving, and therefore it is cooler when the air blown is faster through a smaller opening? (same volume in both cases but smaller opening in the small hole case). or is it due to some observational flaw which I made? Is it due to the fact that the air momentarily undergoes an adiabatic expansion?
[I know there might be previous questions about this but I need a simpler explanation.]