How does a thermos keep stuff hot (or cold)?!
Answers:
A practical vacuum flask is a bottle made of glass, metal, or plastic with hollow walls; the narrow region between the inner and outer wall is evacuated of air!. It can also be considered to be two thin-walled bottles nested one inside the other, and sealed together at their necks!.
Using vacuum as an insulator avoids heat transfer by conduction or convection!. Radiative heat loss can be minimized by applying a reflective coating to surfaces!.
The contents of the flask reach thermal equilibrium with the inner wall; the wall is thin, with low thermal capacity, so does not exchange much heat with the contents, affecting their temperature little!. At the temperatures for which vacuum flasks are used (usually below the boiling point of water), and with the use of reflective coatings, there is little infrared (radiative) transfer!.
The flask must, in practice, have an opening for contents to be added and removed!. A vacuum cannot be maintained at the opening; therefore, a stopper made of insulating material must be used, originally cork, later plastics!. Inevitably, most heat loss takes place through the stopper!.
Www@FoodAQ@Com
Using vacuum as an insulator avoids heat transfer by conduction or convection!. Radiative heat loss can be minimized by applying a reflective coating to surfaces!.
The contents of the flask reach thermal equilibrium with the inner wall; the wall is thin, with low thermal capacity, so does not exchange much heat with the contents, affecting their temperature little!. At the temperatures for which vacuum flasks are used (usually below the boiling point of water), and with the use of reflective coatings, there is little infrared (radiative) transfer!.
The flask must, in practice, have an opening for contents to be added and removed!. A vacuum cannot be maintained at the opening; therefore, a stopper made of insulating material must be used, originally cork, later plastics!. Inevitably, most heat loss takes place through the stopper!.
Www@FoodAQ@Com
There is a pocket of air between the surface the liquid contacts and the outside of the thermos!. This air is a vacuum that minimized the conduction that transfers heat in or out of the container!.Www@FoodAQ@Com
This might help
scroll down to Theory
http://en!.wikipedia!.org/wiki/Vacuum_flas!.!.!.Www@FoodAQ@Com
scroll down to Theory
http://en!.wikipedia!.org/wiki/Vacuum_flas!.!.!.Www@FoodAQ@Com
"he" doesnt need a thermos to keep me hot!.!.!.!.*ahem*!.!.!. anyway, what was the question!?
Cheers mona =)Www@FoodAQ@Com
Cheers mona =)Www@FoodAQ@Com
Uh, its brain reacts to what is put in it, yeah I know great answerWww@FoodAQ@Com