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View Full Version : Why isn't water evaporating in my room?!?


Vorona
09-22-2003, 10:13 AM
Apparently I've got a very odd phenomenon in my room.

I live up in the attic, and I've noticed that water doesn't evaporate up there. No kidding. I brought a glass of water about a month ago, drank about half of it, put it down on a seldom-used area. Just noticed it yesterday -- the water's still there, half full.

I'll have a vase of flowers. The flowers die, I throw them out. *Months later*, the water is still in the vase (so I'm a little lax in rinsing out vases, ok?).

So what's going on? Bad air circulation? Paranormal phenomenon? What? This is too creepy for words!


PS I live in New York City, in case anyone is wondering what the climate is, if that has anything to do with it.

PPS The water evaporates just fine in the rest of the house.

StarvingButStrong
09-22-2003, 10:17 AM
Weird. I assume the attic isn't air tight (or you'd be dead from CO2 accumlation) so air must be being exchanged with the rest of the house and the outside. So it's unlikely humidity is sitting at 100% constantly which would keep things from evaporating.

Unless you have some constant source of water available in the attic to keep it humid? Fish tank, hot tub, huge number of plant pots?

Maybe it's a story for the XFiles.

Q.E.D.
09-22-2003, 10:17 AM
Water won't evaporate if the ambient humity is around 100%. Get a cheap indoor thermometer/hygrometer from Radio Shack or someplace and measure the relative humidity.

Vorona
09-22-2003, 10:32 AM
Nope -- no plants (except for occasional flowers), no fish, no fountains, nothing. I have the windows open almost all the time (except for when it's deathly hot in the summer and I have the a/c on) or when it's deathly freezing in the winter.

But water doesn't evaporate in the winter, either -- and it's certainly not 100% humidity then (I know cause of the problems I have with fly-away hair!). This pheno lasts all year round.

Maybe this is a problem for Cecil!

robby
09-22-2003, 12:49 PM
Originally posted by Vorona
Nope -- no plants (except for occasional flowers), no fish, no fountains, nothing. I have the windows open almost all the time (except for when it's deathly hot in the summer and I have the a/c on) or when it's deathly freezing in the winter.

But water doesn't evaporate in the winter, either -- and it's certainly not 100% humidity then (I know cause of the problems I have with fly-away hair!). This pheno lasts all year round.

Maybe this is a problem for Cecil!

Sorry, I call baloney. There's no need here for Cecil or paranormal explanations. You just need to check all of the conditions a little less anecdotally--i.e. measure the net rate of evaporation at different times of the year, and measure the relative humidity.

Evaporation is a very well understood process (from a statistical/thermodynamic point of view). Strictly speaking, the rate of evaporation is dependent only on the type of liquid in question, the surface area, and the temperature of the liquid.

The rate of condensation back into the liquid is dependent only on the partial pressure of the gas phase of the liquid and the surface area of the liquid. In this case, the first condition corresponds to the relative humidity.

If the relative humidity in the attic is 100%, the water in a container is evaporating at the exact same rate as the rate of condensation. In this case, the level of water would remain constant, and the net rate of evaporation would be zero.

Also note that in the winter, the rate of evaporation is lower (due to the lower temperature of the water), and the water vapor partial pressure is also lower. 100% relative humidity in the winter may not feel particularly humid to you.

Alereon
09-22-2003, 01:26 PM
Also, note that a glass of water, and also a vase, methinks, are going to have a very small surface area relative to the volume of water. Therefore, you're not going to notice much water losss due to evaporation. Try hanging up a damp cloth and seeing how long it takes to dry.

Vorona
09-22-2003, 01:34 PM
Thank you for your answer. Could you possibly repeat it in English? Honest, I've never been accused of being stupid, but I really didn't understand it.

"Strictly speaking, the rate of evaporation is dependent only on the type of liquid in question, the surface area, and the temperature of the liquid."

The type of liquid: always water.
Surface area: Either glass or vase (of various sizes)
Temperature of liquid: Room temperature (so I guess anywhere between 60-90 degrees, since I don't regulate it while I'm at work).

"100% relative humidity in the winter may not feel particularly humid to you."

Why are you insisting that I have 100% humidity in my room in the winter?

Vorona
09-22-2003, 01:37 PM
You know when I really notice this? When I picked up a vase that I hadn't used in at *least* 8 months and it felt very heavy. I noticed that it *still* had water in it! Wouldn't you think that the water would've evaporated by then? I mean, humidity aside, 8 months is about 3 different seasons -- why didn't it evaporate at all in that time?

And as I've said -- I've noticed this does *not* happen downstairs in the first floor.

Rocketeer
09-22-2003, 02:18 PM
The lower floors of the house are warm and full of people, so the air is absorbing lots of water from dishes standing in the sink, house plants, peoples' breath, toilets, baths, etc. Because warm air moves upward, your attic room is getting all that humid air, so water in the attic isn't evaporating at all, because the air is already holding all the water it can.

If your attic is cooler than the rest of the house, that makes it worse, because cold air will not hold as much water as warm air. So the air coming up from the downstairs is, say, 72 degrees Fahrenheit and 80% saturated (that is, holding 80% of the water it could hold at 72F). But it cools as it enters your attic and becomes even more saturated and less likely to absorb more water from your vase. If it cools enough to become 100% saturated, it'll never absorb anywater from your vase.

There are charts, called psychrometric charts, which tell you how much water air at any given temperature can hold, but it's been a long time since college thermodynamics ;) and I'm pretty rusty.

Vorona
09-22-2003, 02:34 PM
I guess that makes more sense -- although the attic is *always* about 10-15 degrees *hotter* than downstairs (which is usually why I leave the windows open all winter, except when there's a bitter wind).

But still -- why wouldnt the water evaporate in the winter when there's no humidity? (Trust me, there aint *no* humidity -- I brush my hair and the static makes me look like a banshee. Don't anybody tell me there's humidity in that room in the winter!!). Wouldn't one think that *no* humidity would cause at least *some* evaporation? I'm serious, the water in my room acts like concrete!

Crafter_Man
09-22-2003, 03:19 PM
The bottom line is that, unless the RH is 100%, the water in the glass and vase must be evaporating. And as already mentioned, if the ratio of surface area to volume is small, you might not notice it.

To prove water is evaporating, take a damp cloth and wipe a smooth, flat object with it (glass, etc.). Note that the thin coat of water makes the surface shiny. Then come back in an hour or two. Is there still a thin coat of water on the surface?

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