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Why vacuum flask keep cold liquids cool better than hot liquids warm?
Wiki User
∙ 13y ago
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.
Wiki User
∙ 13y ago
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Why is the inside of a vacuum flask shiny?
To reflect radiation back, where from it is coming. So hot contains will remain hot and cold will remain cold.
Does a thermos freeze liquid?
A vacuum flask keeps hot things hot & cold things cold. Just how it tells the difference is one of the mysteries of the scientific world !
Why a thermaflask has double walls?
The double walls are required to contain a vacuum which prevents the transfer of heat, so the contents of the flask remain hot (or cold) for longer.
Where do you get vacuum in the vacuum flask?
The flask works because there is a gap between the inner and outer walls of the flask. During the manufacturing process the air in the gap is extracted and the opening is sealed - creating a vacuum between the walls. Heat transmits rapidly through air - but a lot less rapidly, in fact only very, very slowly, through a vacuum. A vacuum flask not only keeps heat in, it also keeps it out. If you put iced water into a vacuum flask it will stay cold for a very long time.
What is a vacuum flask made of?
A vacuum flask is a type of flask that aims to stop all three forms of heat transfer. Conduction, convection and radiation. A vacuum flask prevents conduction by making a vacuum between the inside and the outside layer of the flask, so that the only solids that touch are the lid and the main body of the flask. This means the amount of conduction that occurs is minimised. One major drawback though, is when the hot water transfers heat with the cold air inside the flask, then the hot air transfers heat with the cold lid, and then on the likely chance that the lid is hotter than the surroundings, the lid transfers heat with the air molecules around it. This means that a considerable amount of heat is lost to the surroundings. The only way convection can occur is by the hot liquid or solid transferring heat with the trapped air inside the flask, although this only affects the temperature of the water by a bit, because most of the liquid condenses again. The flask is made so that radiation is reflected back of the sides, which is made of a shiny material. Also, the flask is not transparent; it is made of an opaque material, usually plastic or metal. The only way radiation can escape, is by the lid being taken off.
What is the name of the thing used to keep liquids warm or cold?
Vacuum flask.
Why your vacuum flask cannot maintain the cold anymore?
There could be a crack or leakage that allows air to flow in or out of the flask. It may be time to replace the flask with a new one.
How does vacuum flasks keep hot liquids hot and cold liquids cold?
by inhibiting heat conduction
Why can cold water in an uncapped vacuum flask still stay cold?
It will certainly not stay cold as long as if it were capped.
The presence of -------------- in a thermos flask keeps the substances either hot or cold?
A vacuum is the answer.
What Vacuum flask keeps liquid at same temperature?
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.
Why is the inside of a vacuum flask shiny?
To reflect radiation back, where from it is coming. So hot contains will remain hot and cold will remain cold.
How does hot water becomes cold in a vacuum flask?
Its because there are contact points between the inner part of the flask and the outer part, which allows some thermal conductivity to occur.
What is the main disadvantage of using metal instead of glass in a vacuum flask?
becuase metal conducts heat
Why does the hot tea in a Thermos flask remain hot for a long time?
The Thermos (vacuum) flask has a double skinned glass cylinder inside. Between the two walls of the glass cylinder is a vacuum. The glass cylinder is also silvered on all inner and outer surfaces. Both the vacuum and the silvering help to prevent the rapid cooling of a hot liquid, or the warming of a cold liquid. The vacuum inhibits heat transfer by conduction. The silvering reflects the heat and inhibits the heat escaping from the flask. Thermos (often used for a vacuum flask) is a trade-name.Eventually, as anyone who uses a vacuum flask, the once hot drink will have become cool by the end of the day.
Does a thermos freeze liquid?
A vacuum flask keeps hot things hot & cold things cold. Just how it tells the difference is one of the mysteries of the scientific world !
What is the Functions of thermos flask with diagram?
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.
