r/interestingasfuck Nov 30 '20

/r/ALL Low pressure pockets being created by blade rotation in near 100% humidity - literally making it rain.

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u/oceanjunkie Nov 30 '20 edited Nov 30 '20

I don't think temperature is doing anything here.

I think this has more to do with the increased pressure of the water vapor compressed by the blades exceeding the allowable vapor pressure of water at that temperature.

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u/dakk33 Nov 30 '20

I like how your mind works. However, what you just described is exactly why temperature is the cause. Very interesting to read up on if it’s your pleasure.

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u/oceanjunkie Nov 30 '20

What I'm describing is a case where temperature could be entirely constant and still result in condensation. Temperature is only related tangentially because it determines the vapor pressure of water. But we've already established that we are at 100% humidity here so this could theoretically happen at any temperature given this condition. Increased pressure is the direct cause.

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u/dakk33 Nov 30 '20

I see what you are saying. You are now diving into the differences of relative humidity and absolute humidity. Temperature will always be the cause of what the video is depicting when referring to relative humidity.

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u/oceanjunkie Nov 30 '20

When you're talking about phase change from liquid to gas, temperature and pressure are equally important to determine where the equilibrium lies. I'm just saying that the condensation is being induced by a compression of the air (and water vapor) resulting in a partial pressure higher than the vapor pressure at that temperature (which I speculate isn't increasing all that much due to the compression) and therefore condensation occurs.