Can a Perfectly Insulated Thermos Keep Liquid at the Same Temperature Forever?

[korneld]

Say, you could create a thermos that is perfectly insulated from the environment. No heat going in and out 'till the end of time. If you put boiling-hot water in it, would that water stay the same temperature forever?

What I am curious about is if friction or something else would gradually wear the molecules down, or the conservation of energy would keep that from happening?

Thanks.

 

[timthereaper]

The 2nd Law of Thermodynamics let's you because you're not increasing entropy. However, in real systems, there's always friction and energy transfer unless you find a way to make molecular collisions inelastic.

 

[Lsos]

The 2nd Law of Thermodynamics let's you because you're not increasing entropy. However, in real systems, there's always friction and energy transfer unless you find a way to make molecular collisions inelastic.

Won't the friction turn the heat energy in the thermos bottle into, well, heat?

Or another way of looking at it, won't the friction of one molecule against another simply transfer the momentum (and therefore heat) of that molecule to the other?

...and either way, the total heat of the system will remain unchanged?

 

[lalbatros]

There is no perfect thermos and thermodynamics is an idealisation of reality.
How could you shield the fluid inside the thermo from any gravitational influence?
How could you build a thermo that would shield the fluid from absolutely everything?
What about gamma rays?
Would that thermo become an isolated universe?

In practice, a cofee thermo could keep cofee hot for a few hours.
How could you build a thermo that would keep it hot for a year?
Try to calculate this.

How could you keep the fluid from any sound, if not by a huge isolation?

At a certain point the experience would become almost impossible for many reasons.
Huge amount of money.
Huge time to get this thermo in steady state!

Thermodynamics is a mathematical theory.
It is extremely useful as long as one stay practical.
Just as with any branch of mathematics!

 

[timthereaper]

The Thermos, a plastic rendition of the Dewar flask, does a good job of prohibiting the 3 types of heat transfer: conduction, convection and radiation. In theory, if you used perfect materials and flawlessly constructed it, you possibly could keep the heat indefinitely. However, we can't get perfect except in theory.

 

[NobodySpecial]

In theory, if you used perfect materials and flawlessly constructed it, you possibly could keep the heat indefinitely. However, we can't get perfect except in theory.

Except you would still get evaporation from hot liquids

Always annoyed me how a dewar could keep liquid nitrogen at 200deg below room temperature for weeks but you couldn't get one that would keep coffee at 60deg above room for more than a few hours.

 

[timthereaper]

Except you would still get evaporation from hot liquids

I don't think you would if the container was sealed, which would need to happen if you were to "perfectly" insulate the liquid of choice.

I do agree with the coffee/hot drinks argument though. You get heat where you don't want it and never get enough where you do.