Many question about water(condensation evaporation)

[kevin_tee]

Why water condense when high pressure was applied and reduce to lower pressure?(I observe this when I play with water rocket, when I pump air inside there are no vapor, but after I shoot it, there is vapor coming out.)
Does water condense at 100%< humidity?
Does water vapor condense easier when it is heated? (When I boil water, it seems to condense easier)
Are there water vapor semipermeable membrane? (let air pass through, but water vapor can't.)
How many possible ways to condense water?(cooling etc)

Thanks to every comments

 

[Borek]

Some of the processes you observed are easy to explain by temperature changes.

 

[kevin_tee]

So does water vapor condense when it was pressurize and then depressurize?

 

[Borek]

Because of temperature changes. When you compress the air, it heats up ans starts to cool. When it expands it cools down, but as it lost some of the heat to the surroundings, it now cools down to the temperature that is lower than the initial one - and water vapor becomes saturated. Quite possible in the meantime the air - which, if I understand correctly the situation, was all the time in the contact with water - became saturated to a higher degree, which means condensation even easier.

 

[kevin_tee]

Thanks for your reply, but I didn't understand "Quite possible in the meantime the air - which, if I understand correctly the situation, was all the time in the contact with water - became saturated to a higher degree, which means condensation even easier." what does that mean? Thanks again.

 

[Borek]

In a closed vessel air that is above water sooner or later becomes saturated. Even if you don't wait long enough to have the air saturated (relative humidity 100%), it still becomes closer to saturation than the air you started with.

 

[kevin_tee]

Thank you so much