Understanding Evaporation and Cooling: Physics Problem Explained

[danago]

Hey. If i jump out of a swimming pool, into a breeze, i feel cold.

Is this because the breeze is moving the more moist air away from my body, allowing more evaporation to occur, cooling the water, and since two substances of different temperatures naturally want to equalize in temperature, heat is transferred from my body to the water, thus making me feel cooler?

Is that theory correct? or am i completely on the wrong track? also, what other factors contribute to my cooling after jumping out of the pool?

Im just trying to fully understand these concepts in physics, since it is the subject i am struggling the most in at the moment.

Thanks,
Dan.

 

[HallsofIvy]

Since you headed this "evaporation", you should mention "heat of evaporation". Your body loses heat when water evaporates off it, making you feel cooler. Yes, it is true that the breeze contributes by moving the air, made more humid by the evaporated water, away from you body so that less humid air, which can accept more evaporated water takes its place.

 

[danago]

Since you headed this "evaporation", you should mention "heat of evaporation". Your body loses heat when water evaporates off it, making you feel cooler. Yes, it is true that the breeze contributes by moving the air, made more humid by the evaporated water, away from you body so that less humid air, which can accept more evaporated water takes its place.

When you say heat of evaporation, you mean the thermal energy required to change the state of the water, from liquid to steam?

 

[In_Development]

Well, from what I remember (though it is possibly oversimplified) is that evaporation causes cooling. This is because of the endothermic nature of evaporation, the intermolecular bonds require the intake of energy in order to break and for the separate molecules to move apart (hence taking on gaseous form).

One of the aspects that affects rate of evaporation is the saturation of the surrounding air. If there is an abundance of water molecules (basically the air is humid) then evaporation will slow down. Therefore, when there is a breeze, the saturation of the air is decreased as the newly evaporated particles are moved away from your body allowing for more to evaporate, hence increasing the rate of evaporation and the rate at which energy is taken in from the surroundings to fuel the process... I think this is correct but don't take my word for it!

EDIT: I think I basically just repeated what the other post said... just in different terms, DOH!

 

[danago]

ok, but what other factors affect the cooling in this situation, or is evaporation due to a breeze the only major one id need to consider?

 

[In_Development]

Well, off the top of my head, the other factors that affect rate of evaporation are:

1. An increased surface area : volume ratio, which I believe is rather unlikely to spontaneously occur on your body!

2. Increased heat input from the surroundings... This won't really cool you per se because the overall heat has to increase anyway.

Therefore, as far as evaporation goes, the breeze is the prime factor affecting it. When concerned with other possible reasons for cooling occurring I can't really think if any.

 

[danago]

ok thanks for the help.