Why Can The Thermos Be Kept Warm?
May 18, 2022
Heat travels in three ways: radiation, transfer, and convection.
1. Radiation
Have you ever had this kind of experience? Some thermos cups are made of ceramic or purple sand, and their thermal insulation effect is not as strong as that of pure stainless steel. Although they are all two-layered, they cool quickly.
Of course, part of the reason is that the middle is not a vacuum layer, and part of the reason is that the silver cup on the inner wall of the pure stainless steel thermos cup can reflect the radiation of hot water heat.
You have seen the inner liner of the thermos, and there is a silver coating on the inside and outside. That is the reason. As the service life increases, the thermal insulation effect will decrease after the coating peels off.
2. Pass
There will be a vacuum layer between the inner wall and the outer wall of the vacuum flask. The function of the vacuum layer is to reduce heat transfer. Sound cannot be transmitted in a vacuum, and the same is true for heat.
3. Convection
This vacuum layer can block the water temperature in the cup from being transmitted to the outside, and can also block the external temperature radiation from entering the cup. This blocking effect is mutual. Therefore, the hot water in your cup will cool down very slowly, and the cold water in the cup will heat up very slowly.
2. How does the heat of the vacuum flask dissipate?
Let's talk about the thermos again. Why is the lid of the thermos a cork stopper, or a hollow plastic shell stopper?
Because the air inside these two materials accounts for a large proportion, the thermal conductivity is poor. It’s just poor. In the final analysis, it still conducts heat. In addition, the mouth of the bottle, the place that directly contacts the air, is the two places where the thermos loses the most heat.
The vacuum effect of the cup body of the regular big manufacturers can still be guaranteed, that is, for the pure cup body, there is no major problem with heat preservation.
The same is true for the thermos, and it is also at the lid and the mouth of the cup. But in the end, the lid of the cup is on the mouth of the cup, and in the end, you have to take the lid to talk about it.
