a hot object loses heat to the surroundings by radiation convection and conduction similarly a cold object gains heat from the surroundings by the same three modes to keep a hot body hot we need to reduce the loss of heat and to keep a cold body cold we need to reduce the gain of heat due to these three modes how does a thermos flask work a vacuum flask or thermos is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the surroundings of the flask instead of containing any
kind of heating or cooling element so as to keep hot things hot and cold things cold a thermos is designed in such a way that it minimizes transfer of heat by not allowing heat to escape or enter easily heat can be transferred to the air to keep heat from escaping you need insulation the best insulator possible is a vacuum where there is no air a thermos consists of two flasks here the two flasks are indicated with the colors red and gray they are placed one within the other and are joined at the neck using a
stopper made of an insulating material the gap between the two flasks is evacuated of air during its construction and this creates a near vacuum which significantly reduces heat transfer by conduction or convection the outer casing of a thermos flask is made up of plastic or metal plastic being a poor conductor of heat acts as an insulator preventing the heat loss through conduction inside the plastic case is another double walled container which is made of glass or stainless steel both of the walls of this container are silvered the narrow region between the inner and the outer
walls is evacuated of air and is sealed together to create vacuum this prevents heat loss through convection since there are no air particles to carry out the transfer of heat the silvered and shiny surfaces of the walls also further prevents heat loss through radiation these features in the thermos prevent heat transfer by either conduction convection or radiation the vacuum prevents conduction and convection of air this is because both conduction and convection need molecules of a medium for the transfer of heat the tight stopper prevents air from entering or leaving the flask so this too prevents
convection when radiation tries to leave the hot liquid the silvered surfaces reflect the heat back thus reducing radiation hence with very little heat escaping a hot drink stored in a thermos will stay steaming hot for several hours it is also the same for cold drinks heat is unable to easily penetrate into the flask from the outside environment the sealed stopper prevents conduction as it stops heat from getting in the flask the vacuum stops conduction and the metal lining between the outer case and the inner chamber prevents heat radiation although some heat still escapes or gets
in through the stopper thermos flasks are still a vast improvement compared to other insulated drink containers so these are all the features which help a thermos flask store hot and cold drinks to get more answers to the latest hots questions subscribe to our youtube channel and visit our website
