Wet bulb temperature and water evaporation 1

[Bobfd7dbf]

Hello

Does water stops evaporation process when it's temperatue is equal to the wet bulb temperature of the ambient air ?

If it doesn't,Why the water temperature does not drop less than the wet bulb temperature ?

Thanks in advance.

 

[Compositepro]

Evaporation will stop when the air temperature (dry bulb) equals the wet bulb temperature (100% relative humidity). Heat for evaporation comes from incoming air. Water cannot drop below wet bulb temperature of the air because this will cause condensation (not evaporation) and warming of water to wet bulb temperature.

 

[Bobfd7dbf]

Thank you for your reply.. i am talking about if the air is not saturated and it passes over a stream of water with a temperature equals to the wet-bulb temperature of this air ..why doesn't the evaporation process take place in this case ??

 

[Compositepro]

Evaporation does take place. This is because air with a dry bulb temperature above the wet bulb temperature (less than 100% RH) will add heat to the water to cause evaporation. The temperature of the water will stay at the wet bulb temperature.

 

[Bobfd7dbf]

It's clear sir,
But how does evaporation takes place without cooling the water ??
Evaporation of water will make the particles with the highest energy evaporate and therefor the temperature will drop .
So i want to understand how does evaporation take place in water with temperature equals to the wet bulb temperature of the air without a decrease in temperature??

I hope you know what i mean and thank you.

 

[3DDave]

The warm air heats the water and keeps the water temperature from decreasing. At some water temperature the heat lost to evaporation equals the heat gained from the air.

 

[Compositepro]

"But how does evaporation takes place without cooling the water ??"

That is due to the difference between latent heat and sensible heat. When a liquid boils, liquid changes from liquid to vapor with no change in temperature, but a large transfer of heat. The situation you describe, where the liquid is at wet bulb temperature, is where evaporation transitions to boiling so there is no bubble formation.

 

[IRstuff]

A swamp cooler's water reservoir does cool down on the surface, but on a hot day, the reservoir gains back heat from its container, which is exposed to the ambient. The same case can be made with a puddle of water sitting on a surface; it's constantly losing energetic molecules of water through evaporation, but it regains energy conducted from the surface itself and the air as well.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm