Question

last summer was usually hot. to keep cool, my wife brought several electrical fans that were running all the time in our sun-exposed kitchen. whenever someone was not in the room, i turned the fans off but she immediately turned them back on. can you explain to me, so I can then explain to her, by using the second law of thermodynamics, the following: why it feels cooler to me in front of the fan; why turning the fans off when nobody is in the kitchen is the right thing to do to keep the kitchen as cool as possible.

Answer 1

Why it feels cooler in front of the fan?

Answer:

The real fact is, actually the fan will not cause a cooling effect, in reverse it will produce heat. This is because a fan will convert electrical energy into heat energy. For example, if there is a closed room, with an electric fan running, heat is generated in the room. So it is clear that the fan does not make a cooling effect in the room.

The cooling effect of the fan is due to the wind chill reaction.The wind chill reaction is referred as the increase in the alterated heat reduction by the wind. The fan will blow the air, as a result, there will be an evaporation of sweat in our skin occurs due to the air. When the evaporation rate is higher, the more will be cooling effect.

Why turning the fans off when nobody in the kitchen is the right thing for maintaining the cooling effect as possible

When there is nobody in the kitchen it is advisable to switch off the fan, for power consumption. Addition to that it produce more heat energy to the kitchen, if nobody is there. This can be explained by the basic rules of a ceiling fan while running.

As soon as the fan is turned on the electrical energy enters into the motor. Lack of motor's efficiency, part of electrical energy gets converted into the heat energy which gets collected in the kitchen. Rest of the electricity which creates movement in the air and transformed as heat in the kitchen. As mentioned before, fans will evaporate the sweat, and makes the body cool. Our skin will ensure this process. Since nobody is in the kitchen and the skin is not exposed for evaporation of sweat, for feeling the movement of the air, there is no use of fan, and it simply produce heat energy to the Kitchen.