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Internal Structure Of Vacuum Flask
- Jan 23, 2018 -

   To make a container like a thermos, one way is to take a pot and wrap it in a foam insulation.There are two reasons why adiabatic materials work.First of all, plastic in a bubble is a poor conductor of heat. Second, the trapped air in a bubble is less conductive to heat.So it reduces conductivity. Since the air is separated into tiny bubbles, the foam insulation is largely responsible for eliminating the convection inside the foam. So there's very little heat transfer going through the bubble.
   The fact is that there is a better insulator than a bubble -- a vacuum. A vacuum is no atom.A complete vacuum does not contain any atoms. It is almost impossible to achieve a complete vacuum, but you can get close to the vacuum, without the atoms, you can completely eliminate the conduction and convection.
   There is a vacuum in the thermos bottle. Inside the thermos is the glass layer, which is surrounded by a vacuum. The glass bottle is easy to break, so wrap it in a plastic or metal shell. Many thermos are actually able to rotate and take out the glass jars.
   The thermos is a step closer. The glass was plated with silver (like a mirror) to reduce infrared radiation. The combination of vacuum and silver has greatly reduced the heat transfer caused by convection, conduction and radiation.
   So why do the things in the thermos eventually cool down? In the figure, you can see that there are two heat transfer paths. The larger one is the cork, the other is the glass, which creates a heat transfer path in the area where the top and bottom of the thermos are transferred. Although the heat transfer through these paths is rare, it is not without.
   Does the thermos know that the liquid inside is hot or cold? I don't know. What the thermos does is restrict the heat transfer through the wall of the thermos. That keeps the liquid inside the thermos for a long time, almost constant, hot or cold.