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How Does a Vacuum Flask Work?

Vacuum insulation is one of the best ways to keep the beverage in the thermos hot for a long time. The vacuum is used to prevent the heat from losing and the cold air from entering. On the surface, this principle seems relatively simple, but it actually contains some physical phenomena: heat conduction, convection, and heat radiation.

So, how does the vacuum flask work? 

Thermodynamics points out that there are three ways to conduct heat:

1. Convection: The phenomenon in which fluid flows by itself and takes away heat;

2. Heat conduction: Heat transfer occurs between contacting objects due to temperature difference;

3. Thermal radiation: a phenomenon in which an object transfers heat in the form of electromagnetic waves;

For vacuum flasks, the specific methods of these three ways are:

1. In a vacuum flask, there is a layer of vacuum interlayer, the inside and the outside of which are called "inner tank" and "outer shell" respectively, and a high vacuum is drawn between them. Without air, the convection between the inner tank and the outer shell is minimized.

2. The inner tank and the outer shell are basically not in contact with each other, and there is no solid support in the middle. Only at the top, the insulation is used to connect the inner tank and the outer shell as a whole to minimize heat conduction.

3. A good vacuum flask will also have a reflective layer inside to reflect the heat transferred from the inner tank due to thermal radiation to the greatest possible extent.

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