Me and my dad were arguing last day about this question: suppose it is a very hot day, and the temperature in my room is about $30$ Celsius degrees. There is no air conditioner on, no fan, nothing. The room has a window on which the Sun is shining, and the window is closed with the roller shutter raised halfway.
There is only a door.
Now the question: I state that is I put a fan inside the room and I turn it on, and I close the door leaving the window closed too, what the fan will do will be just to move the (hot) air inside the room, and the temperature won't change (or it will change in a very subtle way, like $29.5$ Celsius degree after a while).
My dad instead said that the fan will make the room less hot due to the air movement by the fan.
Who is right? I believe I am right, since the air in the room won't change its temperature just by being moved, and the fan doesn't produce any cold effect (on the contrary, by Joule effect there is a little amount of heat produced by its engine, right?).
What is the correct reasoning?
Best Answer
I would say you are correct. The reason a fan cools you down is due to evaporation of sweat. A fan does not lower the temperature in any way it does however as you mentioned increase the temperature due to all energy from the fan in the closed room will eventually be converted into heat.