Thermos advice

[andy]

How do they know to keep hot things hot and cold things cold?

Well, Thermo, it's like this. The insulation allows a minimum of heat transfer, regardless of whether the substance is hot or cold to start with. This means that cold things stay cold, and hot things hot.

what about warm stuff inside it?

 

[securespark]

The computer says, "no".

 

[Thermo]

i can never work out where the batteries go on mine

 

[Nige F]

Well, Thermo, it's like this. The insulation allows a minimum of heat transfer, regardless of whether the substance is hot or cold to start with. This means that cold things stay cold, and hot things hot.

oh so its not got a little computer inside then?

No . it`s got a vacuum between the inner and outer glass. The silvering (like a mirror) helps too Thermos is like Hoover, generic name is "Vacuum Flask"

 

[Steve]

The vacuum stops transfer by conduction - no particles in between the 2 glass tubes, so nothing to transfer energy to and through.

Silvering stops transfer by radiation - it reflects radiated heat back into the liquid.

Since no heat can get through by these 2 methods, convection is also out of the question, since this is the transfer of heat through movement of air / liquid. The air outside the flask cannot be heated, since the outside of the flask is cold!

Therefore the weak part of this is the lid, which does not have a vacuum. Silvering still allows transfer by conduction, since it is made of particles which always conduct heat.

 

[Thermo]

oh but how does it tell the difference between soup and tea cos soup seems to stay warmer much longer, is there a little sensor inside?

 

[Steve]

oh but how does it tell the difference between soup and tea cos soup seems to stay warmer much longer, is there a little sensor inside?

You being sarcastic? There are no electronic parts inside, just thermal physics. Soup may have higher thermal mass since it is more viscous.

 

[oilman]

Doubt if soup has higher heat capacity than water, since it has lots of low mass fibre in it. Dry the fibre out, and it can be used as an insulator. (Perhaps that's it, soup is self insulating ) Water is unusual in that it has such a high heat capacity. The soup probably stays warmer, the thicker it is, as the convection currents which bring the heat to the surface, will be lower.

 

[Thermo]

You being sarcastic? There are no electronic parts inside, just thermal physics. Soup may have higher thermal mass since it is more viscous.

I think were going to need a bigger boat to land all these fish!

Er yes i have been stringing along since the start, but i cant believe so many people have gone to such lengthy explanantions to help me understand. Thank you all so much!

 

[Steve]

Thermo, whats your last name?

I can picture it now,

Thermo S. Flask

 

[Thermo]

Nuclear since you ask!

 

[gcol]

Make sure you get a stainless (unbreakable) one though. Those cheaper plastic ones (with a glass inner) are fragile and break. I know because I once opened my flask one dinner time, looking forward to pea and ham soup. Unfortunately the soup was full of broken glass. Was still quite warm though!

 

[Richardp]

Nuclear since you ask!

yes Thermo but isnt your full name Thermo nuclear deuterium-tritium fusion reaction plasma equilibrium. ?
Respect!!