Posted in Kafevend Blog

The challenges endured on any hike through the cold, damp English countryside, any long and arduous climb up the fells of the Lake District, are swiftly dissipated when the trusty Thermos flask is dug out from the rucksack and the hot tea or coffee therein revives our spirits and we muster the strength to carry on. It wasn't always so...

In 1892, Sir James Dewar, a prominent Scottish chemist and physicist, created the first vacuum flask in order to assist him in his study of liquefied gases. By utilizing two layers separated by a partial vacuum, his flasks could slow down the effects of heat transfer, which allowed him more time to study the liquid gases. Unfortunately, he lost out on the earnings his invention could have brought him as he failed to patent the design, which was then taken up by the company Thermos. As such, the vacuum flask is often colloquially known as either the Thermos or Dewar flask.

The vacuum flask works by having two separate layers joined at the neck of the vessel with the space between the two layers filled ( or perhaps, unfilled) by a partial vacuum. The inner vessel, often made of glass is typically silvered on one side. The reason this device is so efficient at maintaining the temperature of the substance it contains is because the vacuum and mirror effect of the silver helps to nullify heat transfer. However, the reason the temperature of your coffee or iced tea doesn't remain constant is due to it being difficult to create a perfect vacuum, and because the vacuum isn't present at the flask's cap. Any supports inside the layers to keep the glass in place will also lead to a temperature change. Nevertheless, you can rely on the flask to keep your drink hot or cold for several hours, certainly long enough for the average day trip!

by Kafevend

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