A thermos flask or vacuum flask is a bit like a super-insulated jug. A typical thermos has an inner glass chamber and an outer plastic one. Between the inner and outer layers there is a vacuum. The outer material can also be made of metal, like stainless steel, for greater durability.
‘As a rule, man is a fool, when it’s cool he wants hot, when its hot he wants cool’! I have a faint recollection of this quote being on my calendar during my school days. Don’t you agree humans can be quite contrarian? When the winter is here, we long for warmth and do whatever we can to keep ourselves toasty. Then, when the summers come, we affix our eyes on air conditioners to shield ourselves from heat—the same heat that we embraced in the winter!
A thermos flask is one such invention that saves us in our contrarian needs. This is not exactly about keeping us warm/cold, but it does apply to our beloved beverages, e.g., coffee, tea, milk etc.
A thermos flask, also called a Dewar flask, is a special kind of bottle in which hot liquids like tea and coffee remain hot and cold items like ice or cold water remain cold for a long time. It is also popularly known by other names, such as a vacuum flask or simply a thermos.
How Thermos Flask Prevents Heat Leakage From The Container?
Now that you know about conduction, convection, and radiation, let’s get back to working of the thermos flask. Now, the main purpose of a thermos flask is to prevent the flow of heat to and from the flask. The inner chamber of the flask is made up of glass, which is a poor conductor of heat. Hence, heat does not flow by conduction. Since there is a vacuum between the inner and outer walls of the bottle, the flow of heat by convection becomes redundant. Finally, the silvering of the walls ensures that the heat is not lost by radiation. As a result, the liquid kept in a thermos flask continues to maintain its heat levels.
This means that the coffee you poured in the thermos in the morning will still be hot/warm when you sip it in the afternoon. Similarly, the cold soda you put in the thermos late at night will still be chilled when you crack it open in the morning.
