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Q & A: vacuum chamber to boil water

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Most recent answer: 11/22/2013
Q:
Hello, How difficult would it be to create a partial vacuum in a chamber say one cubic litre so that water would boil at 15 degrees C. I believe the vacuum would have to be HG 29.42. Would this need an extremely strong chamber and what kind of equipment would I need to do it, or would this just be impossible for me to do without expert and expensive equipment. Thanks in advance if you answer my question. Best regards Mike
- Mike Nettleship (age 63)
Sheffield United Kingdom
A:

The chamber doesn't have to be any stronger than any normal vacuum chamber. The strength needed is just determined by the pressure difference across the chamber wall.  After all, the difference between 0.99 atm and 0.999999999 atm is much less than the normal variation in atmospheric pressure. Really good vacuums require chambers with very good seals and with no porous materials to gradually give off gas, but don't require special strength.

At any rate, you won't need a special vacuum. The vapor pressure of water at 15°C is around 0.017 atm. You can boil water by pulling back on the plunger in a syringe with a standard Luer-lock cap. To boil larger amounts a fairly cheap vacuum pump and a glass chamber with a decent rubber gasket seal should work fine.

Mike 


(published on 10/18/2013)

Follow-Up #1: non-permanent magnets

Q:
Firstly, thank you for answering my last question. I can't find an answer in your questions page. I'm building a wind turbine generator and have a question which I cannot find an answer to anywhere else on the net. Question: I have some neodymium magnets. If I mechanically force two magnets which want to repel each other closely together so that if they were released they would fly apart at speed, does this weaken their magnetic field so the force holding them apart would diminish. If that force would diminish would it be over a short time i.e. a few weeks or months or years. I thank you now in anticipation of your answer. Best regards Mike Nettleship
- Mike Nettleship (age 63)
Sheffield UK
A:

My guess is that the magnetization will decay only over a period of many years, at room temperature. If the magnets are heated or mechanically shocked, however, the decay can speed up a lot.

Mike W.


(published on 11/22/2013)

Follow-up on this answer.