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To keep hot liquids hot and cold liquids cold by minimizing heat transfer between the inside of the thermos with the outside.
During an experiment, James Dewar formed a brass chamber that he enclosed in another chamber to keep the palladium at its desired temperature. He evacuated the air between the two chambers, and through the need for this insulated container, he created the vacuum flask.
If you are using wood, metal, plastic, or a thermos it would have to be a thermos because inside of it there insulators. Insulators are used to keep whatever is inside the same without the stuff outside interfering. Why else do you think we drink hot coffee in a thermos.
Most thermal pots use a vacuum flask inside. The inner and outer walls are separated by a vacuum. The only way heat is transferred from inner to outer walls is by radiation.
They are used to keep hot liquids warm because they are an insulator they're thick and will keep the heat in the liquid longer than just a cup as well they are used because of there coffee cup lid which makes it easy to take with you onto a job site or just anywhere really.
Vacuum flask.
by inhibiting heat conduction
There is no way to permanently store heat. The most you can expect, from a high-quality vacuum flask, is to keep the liquid cold, or hot, for a fairly long time. But gradually, some heat will seep in, or out, until the temperature in the vacuum flask will be equal to the temperature of the surroundings.
The vacuum reduce heat loss by conduction and convection.
Insulation
Hot drinks such as tea and coffee are usually held in a thermos flask. The flask will keep the drink warm for several hours when one is outside or on the move. Cold drinks can also be kept in them or even non drinking liquids that one wishes to keep at a steady temperature.
A Flask
The primary function of a thermos flask is to keep liquids hot or cold. There is an outer protective layer with a hollow area inside before the actual area where the liquid is stored. Heat or cold gets trapped in the hollow area and that is what keeps a liquid hot or cold.
It is due to heat transfer by radiation. You must first understand all objects emit some radiation, even room temperature items, but hotter items release greater radiation. With a hot liquid, the vacuum flask is releasing heat via radiation (radiant heat) outwards into the surroundings, the surroundings mostly absorb this radiant heat, therefore the radiant heat is constantly lost to the surroundings. However, with a cold liquid the radiant heat is transferred from the surroundings to the vacuum flask, where the vacuum flask is a relatively small "target" for the radiant heat to strike. Therefore the cold liquid only receives a small amount of radiant heat from the surroundings and thus changes temperature more slowly. Think of it this way: The surroundings is a very very large "target" for the heat released from the thermos to strike, while the thermos is a relatively tiny target for the heat from the surroundings to strike, thus it is easier for the thermos to lose heat than it is to absorb heat from the surroundings.
Heat can be transferred in three ways: conduction, convection, radiation. In a vacuum flask, conduction and convection are greatly reduced through a vacuum (hence the name!) between two glass layers, whereas radiation is greatly reduced by the mirror coating on the same glass. As a result, heat takes much longer to get out - or in, since you can also keep cold things in a vacuum flask.Note that no vacuum flask will keep things hot (or cold) indefinitely; it simply takes much longer for hot things to cool down, or for cold things to heat up.
It's a flask with a flat bottom. It's used for containing liquids when you don't want to have to use a stand to keep it from tipping over.
a insalator keeps liquids warm