I agree that if you leave the bucket in there, and your vacuum system is any good, that you’ll eventually empty the bucket. But if you have a sufficiently-powerful pump to suck out the air on a timescale shorter than the evaporation timescale, pump out (almost) all of the air, then seal the chamber and leave it there, you’ll end up with a small amount of water evaporated and most of the water still in the bucket, at a temperature only slightly below the original temperature. Or if you don’t like postulating a vacuum pump that fast, then seal the bucket while you’re pumping down, then open the bucket after the chamber is evacuated and sealed. I think this gets closer to what the OP was asking about.
And if your pumping was at the University, it was probably within a few meters of my office, not miles.
I’m sure that we’re in agreement on the physics, Chronos (and I’m very relieved about this!), it’s just different interpretations of the OP. Your “powerful pump sucking out all the air” example is essentially equivalent to stopping at step 3 in my pumping sequence in post #20, assuming that the bucket has enough water that this step is reached. Still, in this case I’d claim that there is never a “vacuum”. Your other example (the bucket being sealed during pumping, then opened when the room was at vacuum) is one that I had not initially seen as a possible reading of the OP, but I’ll accept that he could have meant that.
[Incidentally, my late-night back-of-the-envelope calculations show that if you take a sealed squash court (say 32’ x 21’ x 16’) at 30 degrees C, evacuate it, then open up a sealed 2-gallon bucket full of water in it, essentially all of the water will evaporate and the resulting vapor pressure will be slightly under 32 Torr (i.e. 32mm Hg). If the bucket is 4 gallons, it’ll end up half-full. So, with real-world rooms and buckets, we really are in the transition region between full bucket and empty bucket. Standard disclaimers for late-night back-of-the-envelope calculations apply.]
Back in 1998 I did some collaborative work with this guy in Chemistry at MSU. His research group was about to move into a new on-campus facility under construction at the time, but his laser experiments were temporarily in a lab here, which is about a mile east of the center of campus. It took me about 20 minutes to walk from the lab to the original Pickle Barrel on campus.
I should have added that in my back-of-the-envelope calculation in the above post, the room is evacuated and then re-sealed by closing a valve in the pump line before the water bucket is unsealed. If the room is being evacuated continuously then the situation is the same as my post #20, and the bucket will always end up empty.
The experiment is routinely conducted by refrigeration techs. Only instead of a room, they have a system of tubing, compressor, etc. When commissioning a new system, or after repairs, all the air and water must be pumped from the system…down to less than 100 milliTorr. (1 milliTorr = 1 micron in ref-tech speak)
If the system contains water, they have to pump on it for a long time (perhaps overnight) because the water will evaporate until it freezes. If this occurs in a well insulated portion of the system, it will take hours to sublimate so that the vapor can be pumped from the system.
BTW, 13X zeolyte would make also an excellent pump for the water vapor once you had the majority of the air out. This is the basis for some solar powered (to regenerate the zeolyte) refridgeration systems that have been succesfully demonstrated. (I can explain the failure on “Rough Sceince” if anyone is curious)
Finally, if anyone wants a demonstration of the vacuum “pumping” achievable by a condensor in a steam plant do the following:
Obtain an empty screw top juice carton, with lid.
Put about 1/4 cup water in the carton. Place the lid on the carton, but
DO NOT TIGHTEN IT AT ALL, IT MUST BE LOOSE.
3)Microwave (lay carton on side to fit) for ca. two minutes.
4)Immediatly the microwave stops, open the door, and tighten the lid.
This question has the possibility of some serious applications. Those of you who are familiar with fiberglass yachts know that a significant number of them develop a condition known as osmosis which invariably is associated with a high moisture content in the fiberglass matrix of the hull. Back in the 80’s, I proposed to my employer that we vacuum bag the hull in lieu of heat application to remove that moisture so that we could continue to rebuild and rectify the problem.
We experimented with several square feet whereby we pressed a perimeter caulking onto the hull and applied a nylon film over a coarse fabric within the confines of the sealant to facilitate the extraction of a “airborne” water molecules through a vacuum port under the constant influence of an extraneous vacuum set at 25 inch of mercury. Clearly we allowed for water molecules to escape the confines of the hull fiberglass laminate into a vacuum and provided for constant discharge. To my dissapointment however after two days , the results were negligible. I’m still perplexed as to why the experiment failed. Needless to say, we continued to use heat to effect moisture extraction.
I’m not so sure. There will be some characteristic timescale for the water to evaporate, and there will also be some characteristic timescale for the pump to pull gasses out of the room. If the pump’s timescale is significantly shorter than the evaporation timescale, then you’ll get the room pressure down below 32 Torr, even before the bucket is emptied (how much below 32 Torr would depend on how much faster the pump timescale is). If one used such a fast pump to get down to vaccum (or at least, to almost vacuum) and then sealed the system, the subsequent evolution of the system would be much like the situation where the bucket is sealed while you’re pumping. To be fair, I don’t know if it’s possible to make vaccum pumps which work that quickly.
I also won’t dispute your calculations on just how much water would be left in the bucket (since I haven’t had time to do the calcs yet myself), but I will say that a squash court strikes me as an awfully big room. If you go with something more on the order of 4m x 4m x 3m, you should still have plenty of water left.
And a minor nitpick, but Pickle Barrel isn’t on campus, it’s just across the street.
Well, not better. The point is to have the water boiling for a bit, so that the majority of the air is purged and replaced by steam. If that is done, the carton will completely collapse on cooling, and rather suddenly as well.
Putting hot water in leaves most of the air…the water will give off some vapor, but that quickly cools the water. The hot vapor/water will heat the air a bit, driving some of it out. You get a noticeable decrease in volume on cooling, denting the sides, but it is slow, andnot nearly as spectacular a demonstration.
I used caps on the instruction not to tighten the lid. The resulting explosion would be loud, but not really dangerous. A juice carton will fail at fairly low pressure…a bit more than a paper bag. This is the reason I said use a juice carton, rather than a more robust container.