I have a thermos and just put water at a cold-ish temperature in (below room temperature). Whenever I leave it for long enough, it feels like it gets colder, is this actually possible and happening or am I imagining things? I’ve been told it has something to do with “dead-air” but I don’t understand what that means.
(This is my first time posting in this sub, if this question would fit better at a different sub please tell me)
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A thermos is an insulated container, also known as a dewar. A proper one has an inner and outer glass layer, with a vacuum in the middle of these two bottles to prevent heat transfer.
You’re imagining things.
When you put cold liquid in, the first thing it does is heat up the liquid a bit, because the inner glass layer started out at room temperature, heating up the water. Then temperature remains stable for a long time, but doesn’t get even colder.
You can make the cold last for a long time by pre-cooling your thermos in the refrigerator, or indeed making the water initially even colder if the thermos is first stored in the freezer.
If you are putting warm water and ice cubes in the thermos, it might take a while for the ice to melt and for the liquid portion to cool.
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