There ’s an old caper , that plump a small something like this : a thermos flask can keep raging thing red-hot and cold things cold . But how does it know ?
The joke is that the bank clerk does n’t have it off how a thermos flask works , but it ’s afairly commonquestion and there ’s no disgrace in not knowing how all of your dishware works . Besides , the solvent is pretty interesting .
Unless you are the type who consider the talking dishware subdivision ofBeauty and the Beastwas a documentary , you know that thermoses do not live when they are think to keep matter hot or insensate . So the question becomes : how do thermos flask keep spicy things hot and stale thing cold ? That ’s a small easier to answer , with some good old - fashioned thermodynamics .
Thermoses are middling commonplace today , and largely used for retention , for case , bake beans warm ( yes , we ’re a British publication , get over it ) . But like the microwave was originally invent forheating up dead hamster , thermos flask emerged from non - food - interrelate research .
In the later nineteenth hundred , Scottish pill pusher and physicist James Dewar developed a machine up to of knuckle under orotund quantity ofliquid oxygen . The problem was that liquid O boils at around – 183 ° C ( – 297 ° atomic number 9 ) , and there was no way to keep it coolheaded long enough to study it .
He was fighting the law of thermodynamics ( as you should ) , specifically , the second law , which dictate that heat always flows from hot to colder areas . Yes , we know thesecond law says a lot more than that , but that nineteenth - century intellect is sufficient for talking about the twist that keep your bean warm .
Heat is lost to the environment in three mode ; conductivity , convection , and radiation . Conductionis the heat conveyance that happen through verbatim physical contact , and energy transfer through collision between molecules and speck . Convectiontakes place in fluids , as hotter fluid rises to the top of a system and cooler fluid sink , create convection currents . Radiation , meanwhile , consume shoes through electromagnetic waves breathe as atoms move around or vibrate .
When you place raging coffee in a cup , heat is lose to conduction as the atoms within your cup collide with the sides of it , and the air above , transfer some of their energy to it . Convection helps speed affair up , pitch hot fluid to the top for its turn to be cooled until the temperature of your cup of corpuscle matches the surrounding environment .
Dewar came up with a path to importantly slow down these cognitive operation , though in his case it was to keep a melted cool . In 1892 , he came up with a dewy-eyed , though ingenious , solvent . He simply set one flask within another , separated by a near - vacuum . The vacuum stratum prevents conduction and convection , while inside the flask , he applied a contemplative material to slow down radioactivity .
The system slows the liquids or attic within from being heated by the external environment , or cooled by it if you prefer your beans hot . Dewardid not end up patentingthe arrangement , and improve , smaller flasks soon became cognise by the name " Thermos " after the company obtained a patent for it .
