Weird issue with vacuum flask

Surely by now even the best thermos must have hit equilibrium so have you managed to just pop it apart?
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flask can be just like a kilner jar (a pre-zoomer thing, used for preserving fruit) where the 'vacuum' seal is that good -- it lasts for years at ambiant temp -
but yes, I don't believe a flask is manufactured to that precision, so,
must be another issue in addition to poor threads, like the seal is not rotating with the top, or? the food helped glue it down - starch wallpaper paste.
 
theone8181 said:
But there shouldn't be a pressure difference once it's cooled as the hot contents will not be hot anymore? Or is that the problem, in which case its not kept it warm till lunch so why bother with the flask?
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a pressure differential does not automatically equalize to a thermal gradient as it requires a mass-flow of air particles from atmospheric pressure to a lower than atmospheric pressure.

the op filled a flask with hot food and sealed it. the food then cooled reducing its natural pressure to below atmospheric pressure. in order for this to equalize there must be a transfer of mass from outside of the seal to inside the seal.

whilst the thermal energy has reached an equilibrium, the pressure energy maintains a difference. in order to change then molecules must move from outside the flask to inside, however the sealing of the flask prevents any such movement
 
I realised as I posted it it might be confusing. I can understand a fridge creating a vacuum for the reason you've got, but they've got proper seals on. Do thermos flash gave o-rings and the like, I always thought they were plastic threads with no soft material to compress, in which case the pressure should have equalised by now. If there was an oring in then just ignore what I've said. Are you sure the stuff going in wasn't too hot and has deformed something?
 
theone8181 said:
I realised as I posted it it might be confusing. I can understand a fridge creating a vacuum for the reason you've got, but they've got proper seals on. Do thermos flash gave o-rings and the like, I always thought they were plastic threads with no soft material to compress, in which case the pressure should have equalised by now. If there was an oring in then just ignore what I've said. Are you sure the stuff going in wasn't too hot and has deformed something?
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plastic can and is used as a sealing material- there's no rubber seal on a bottle of coke yet it can hold pressure.
 
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adolf hamster said:
plastic can and is used as a sealing material- there's no rubber seal on a bottle of coke yet it can hold pressure.
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What I mean is that will a none compressible seal, I'm surprised it's sealed well enough to create a vacuum. My job involves building vacuum sealed lasers, so I know how hard is it to seal (I mean proper vaccums). I'd have thought the leak rate would mean it would have equalised by now.
 
theone8181 said:
What I mean is that will a none compressible seal, I'm surprised it's sealed well enough to create a vacuum. My job involves building vacuum sealed lasers, so I know how hard is it to seal (I mean proper vaccums). I'd have thought the leak rate would mean it would have equalised by now.
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it won't be a perfect vacuum, but it doesn't need to be, although going back and looking at the op's link not only has he got a silicone seal to deal with, but also a very large diameter lid which would explain why it's become so tight.
 
theone8181 said:
What I mean is that will a none compressible seal, I'm surprised it's sealed well enough to create a vacuum. My job involves building vacuum sealed lasers, so I know how hard is it to seal (I mean proper vaccums). I'd have thought the leak rate would mean it would have equalised by now.
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Oh right, I get you.

It hadn't equalised after 3 days. And it's gone in the bin now, so that's your last update. :D
 
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