History

A vacuum flask is a type of flask that aims to stop all three forms of heat transfer. Conduction, convection and radiation.

ConductionA 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. 

Issues 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 radiation can escape, is by the lid being taken off.

ConvectionThe only way    convection occur's 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.

RadiationThe 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. 

Designed and invented by Scottish scientist Sir James Dewar in 1892 as a result of his research in the field of cryogenics and is sometimes called a Dewar flask in his honor

The vacuum flask consists of two flasks, placed one within the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which prevents heat transfer by conduction or convection. Heat transfer by thermal radiation may be minimized by silvering flask surfaces facing the gap but can become problematic if the flask's contents or surroundings are very hot; hence vacuum flasks usually hold contents below the boiling point of water

Vacuum flasks are used to maintain their contents (often but not always liquid) at a temperature higher or lower than ambient temperature, at ambient pressure of approximately 1 atmosphere (14.7 psi). Domestically and in the food industry, they are often used to keep food and drink either cold or hot.The thermal wares with wider dia' are being used for storing solid food too.

Use:(Domestically)

How Does it work?

Presently

Stainless Steel Thermos Bottle

Vacuum flasks are at risk of implosion hazard and glass vessels under vacuum in particular may shatter unexpectedly. Chips, scratches or cracks can be a starting point for dangerous vessel failure. There by eliminating glass makes flask a much more sturdy and safe equipment to carry around.

WHY?From Vacuum Glass Flask Thermos to Stainless Steel Vacuum Flask Thermos...

Thermos Flask