What cause vacuum bottles to "lose its vacuum"?
October 2, 2014 8:09 PM Subscribe
I've had a "timolino"thermos/ travel mug from David's Tea for two years, and love it to pieces. I use it everyday, and it used to keep my tea piping hot for at least six hours. In the last few months, the thermos lost its heat-retention drastically-- now my tea is only lukewarm after 2 hours. What could have caused this?
Some googling shows that the thermos has "lost its vacuum," which I took to mean air got into the supposedly vacuum space between the interior and the exterior walls, is that right? What could have caused this? I have a cheap thermos that lasted for years, and this more expensive one barely made two years. Do these things just vary greatly in terms of quality?
Some googling shows that the thermos has "lost its vacuum," which I took to mean air got into the supposedly vacuum space between the interior and the exterior walls, is that right? What could have caused this? I have a cheap thermos that lasted for years, and this more expensive one barely made two years. Do these things just vary greatly in terms of quality?
Response by poster: I dropped it once. I can't see any open seams or anything like that though.
posted by atetrachordofthree at 8:24 PM on October 2, 2014
posted by atetrachordofthree at 8:24 PM on October 2, 2014
Best answer: There's probably a plastic plug of some kind on the bottom of the mug, covering the hole through which the air was removed. The seal around that plug will have failed. Impact might cause this, but putting it through a dishwasher can also do it.
posted by jon1270 at 8:24 PM on October 2, 2014 [2 favorites]
posted by jon1270 at 8:24 PM on October 2, 2014 [2 favorites]
Response by poster: Ah, yes. I definitely put it through the dishwasher a couple of times without thinking. Oh well, onto the next one!
posted by atetrachordofthree at 8:29 PM on October 2, 2014
posted by atetrachordofthree at 8:29 PM on October 2, 2014
I have a cheap thermos that lasted for years, and this more expensive one barely made two years. Do these things just vary greatly in terms of quality?
I've been looking at the Zojirushi travel tea mugs to replace my dearly departed Nissan travel mug. Both are apparently quite solidly made.
posted by sebastienbailard at 2:55 AM on October 3, 2014 [1 favorite]
I've been looking at the Zojirushi travel tea mugs to replace my dearly departed Nissan travel mug. Both are apparently quite solidly made.
posted by sebastienbailard at 2:55 AM on October 3, 2014 [1 favorite]
I can't see any open seams or anything like that though.
A hole in the seam a few O2 molecules wide will destroy the vacuum in a matter of days or weeks, so you won't necessarily see anything.
Fun fact: expensive vacuums are lined with titanium or some other reactive metal, which acts as a vacuum pump. The titanium atoms on the outside are sometimes struck by molecules of gas (because the vacuum isn't perfect), and bond with the gas. This, over time, reduces the pressure inside by removing stray gas molecules one-by-one. Generally, however, this "pump" isn't useful for achieving vacuum - the titanium links are so weak that the next gas molecule will knock the first one off, raising the pressure again, so this "molecular pump" is only useful when the odds of a gas atom striking the area of a titanium atom's bonding cross-section are extremely low.
IOW, if you have a good enough vacuum, this will help preserve it. But preserve it from what? The opposite action: we know that gas molecules are loosely bonded to the irregular, jagged surface of the interior by a variety of bonds, and these slowly release over months or even years. All the titanium does is set up an opposite-direction "drift" in the number of free gas particles, grabbing them (eventually) after release.
When making a vacuum, you go through three stages. In stage one, the gas is so thick/vacuum so poor that you can treat it as a gas, and pump it out normally, like by aquarium pumps, house fans, and most pumps you've ever seen. In the next stage, gas molecules are unlikely to hit each other while traveling across the vacuum container (more likely to hit walls), so nothing you do to one molecule will affect another gas molecule. In this stage, the kinetic molecules have to be removed by fan blades that are moving faster than the molecules themselves, with multiple layers of blades, so that on average the ricocheting of gas molecules at hundreds of miles per hour tend to travel away from the vacuum area. In the third stage, the fan blades are unlikely to even see the gas molecules, and you need a getter/molecule pump like I've described above.
posted by IAmBroom at 2:29 PM on October 5, 2014 [1 favorite]
A hole in the seam a few O2 molecules wide will destroy the vacuum in a matter of days or weeks, so you won't necessarily see anything.
Fun fact: expensive vacuums are lined with titanium or some other reactive metal, which acts as a vacuum pump. The titanium atoms on the outside are sometimes struck by molecules of gas (because the vacuum isn't perfect), and bond with the gas. This, over time, reduces the pressure inside by removing stray gas molecules one-by-one. Generally, however, this "pump" isn't useful for achieving vacuum - the titanium links are so weak that the next gas molecule will knock the first one off, raising the pressure again, so this "molecular pump" is only useful when the odds of a gas atom striking the area of a titanium atom's bonding cross-section are extremely low.
IOW, if you have a good enough vacuum, this will help preserve it. But preserve it from what? The opposite action: we know that gas molecules are loosely bonded to the irregular, jagged surface of the interior by a variety of bonds, and these slowly release over months or even years. All the titanium does is set up an opposite-direction "drift" in the number of free gas particles, grabbing them (eventually) after release.
When making a vacuum, you go through three stages. In stage one, the gas is so thick/vacuum so poor that you can treat it as a gas, and pump it out normally, like by aquarium pumps, house fans, and most pumps you've ever seen. In the next stage, gas molecules are unlikely to hit each other while traveling across the vacuum container (more likely to hit walls), so nothing you do to one molecule will affect another gas molecule. In this stage, the kinetic molecules have to be removed by fan blades that are moving faster than the molecules themselves, with multiple layers of blades, so that on average the ricocheting of gas molecules at hundreds of miles per hour tend to travel away from the vacuum area. In the third stage, the fan blades are unlikely to even see the gas molecules, and you need a getter/molecule pump like I've described above.
posted by IAmBroom at 2:29 PM on October 5, 2014 [1 favorite]
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posted by blnkfrnk at 8:18 PM on October 2, 2014