Thermos Bottle: Stainless Steel Inside & Out - 24h Cold & 12h Hot

[barnabe_fisico]

TL;DR Summary

A thermology question: Keeping different cold and heat in thermos bottle

Manufacturer information:

Interior material: stainless steel
Exterior materials: Stainless steel
Keeps cold liquid for: 24 hours
Keeps hot liquid for: 12 h


I was looking for a thermos bottle and came across a situation that I'm having a hard time answering.
Why is the cold keeping time different from the warm time?

 

[anorlunda]

Summary: A thermology question: Keeping different cold and heat in thermos bottle

Why is the cold keeping time different from the warm time?

Probably because heat loss is proportional to the difference between inside and outside temperatures.

If your room is at 70F, cold water at 40F is 30F colder than the room, but boiling water at 210F is 140F hotter than the room.

 

[DaveC426913]

Heat transfer is proportional to the difference in temperatures. The bigger the the difference in temperature between heat source and heat sink, the faster heat will be transferred.

[nm Anorlinda beat me.]

 

[Dale]

Probably because heat loss is proportional to the difference between inside and outside temperatures.

Maybe also because the range of acceptable "cold beverage" temperatures is different than the range of acceptable "warm beverage" temperatures.

 

[256bits]

Summary: A thermology question: Keeping different cold and heat in thermos bottle

Why is the cold keeping time different from the warm time?

No thermodynamic reason.
( With radiative heat transfer - which is usually what is meant by a thermos - and the same temperature difference between hot and ambient, and cold and ambient. the hot will cool down slightly faster than the cold object. For temperatures of drinks that we consume the difference of power heat transfer is only about 5%, and less as the bodies approach ambient, so not a typical concern at all. )

since they do not define 'hot' or 'cold', or the 'test' conditions. it boils down to whether or not you accept their 'data' on face value, and purchase the product.

 

[willem2]

For temperatures of drinks that we consume the difference of power heat transfer is only about 5%, and less as the bodies approach ambient, so not a typical concern at all

I think the effect is quite a bit larger. Net radiated power across a constant temperature difference goes as the third power of the absolute temperature. (difference between 2 fouth powers). 5% would correspond to a temperature difference of only about 293 * (1.017) about 4 K, where the difference is more like 50K.

 

[256bits]

I think the effect is quite a bit larger. Net radiated power across a constant temperature difference goes as the third power of the absolute temperature. (difference between 2 fouth powers). 5% would correspond to a temperature difference of only about 293 * (1.017) about 4 K, where the difference is more like 50K.

So much for the table napkin calculation.
I get a much larger initial percentage now - 28%.
If hot is closer to 100 C, then the 12 hour cooling could be correct.

 

[Merlin3189]

( With radiative heat transfer - which is usually what is meant by a thermos ...

My experience of vacuum flasks (sometimes Thermos, more often not) is that conduction is a significant route of heat loss (or gain - though I have much less experience of that.)
When I decided to buy a steel vacuum flask, because glass ones were too fragile, I quickly decided to go back to glass, because they do at least retain some heat!
I assume that both have a similar vacuum gap, and I give the benefit of the doubt to steel in hoping that (polished?) steel might be as reflective as "silvered" glass, but I suspect that even thinner stainless steel is more conductive than the glass. At any rate, I found it much less effective than my glass ones.

For both types there is a plug and I also believe heat is conducted through that.