How does a Thermos Work?

Who invented a Thermos Bottle? What is the Working of a Thermos Flask? How can it keep Liquids Hot or Cold for much longer time? What are the Uses?
how does a thermos work

You all love to have chilled and hot beverages depending upon the seasons. And these thermos flasks help you to keep things ready for the go when you are busy with your work schedules. Thermos belongs to the group of containers that keep food hot for hours as well as cold. They have been in use for a century now. Since these flasks are insulated, they keep things at their required temperature for a longer period of time. But how does a thermos work?

1. Who invented Thermos Flask and When?

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A Scottish scientist named Sir James Dewar invented this vacuum flask in the year 1892. He made it while he was researching cryogenics (a study and production of the behavior of materials at very low temperatures). He was producing large quantities of oxygen for industrial purposes when he met with the challenge of finding a way to keep the oxygen at a constant temperature. Also, check out the article what is the average garage door size?

In order to do so, he put a container inside a container, created a vacuum between those containers, and applied a reflective layer to the interior of the bottle. This prevented the loss of heat by any methods of heat transfer. His invention was patented by Reinhold Burger and Albert Aschenbrenner, who began using the Dewar flask (good for insulation) for commercial purposes. (Also read Who invented Paper and When?)

2. What are the Principles used in the Thermos?

There are three principles that define transfer and loss of heat which are, conduction, convection, and radiation. 

  • Conduction is the process of the direct transfer of heat. For example, when ice cubes are in a glass of water, the heat from the water is absorbed by the ice. The ice melts, making the water cold.
  • Convection is a process of heat transfer in fluids where there is a transfer of heat due to the tendency of the hotter (less dense) fluid to rise and the less hot (more dense) fluid to sink. For example, when water is placed in a vessel over the stove, the water molecules at the bottom of the vessel get heated and move to the surface, and the cold molecules sink down and rise up once they’re heated.
  • In radiation, heat transfer happens due to electromagnetic waves. For example, when standing near a heater, you will feel heat waves on your body from the heater.

How does a thermos work and how is it related to conduction, convection, and radiation? Well, the thermos flask is designed in such a way that transfer of heat by all three principles is prevented. (See What Does 3D Mean?)

3. How do Containers that keep Food Hot for Hours Work?

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Basically, these containers are the same as the thermos flask which is a bottle inside another bottle, but there is no contact between these two layers. These two layers are made of glass coated with silver. Nowadays stainless steel is used to provide the silver finish as well as it can also act in the same way as silver, thus making the flask less breakable. There is a vacuum created between them, which reduces the flow or transfer of heat between them. (Also read 7 Metal in Microwave Mythbusters Facts)

4. How does a Thermos Work?

How does a thermos work and how accurate is it? This largely depends on the factor of insulation within. (See Why does Black Absorb more Heat?)

  • The basic function of the thermos flask is that it provides insulation. Insulation is the property of some materials which prevent the passage of heat or electricity to transfer from one conductor to another. Thus, the heat is trapped in it and cannot escape from one layer of the flask to another. So basically the thermos flask works in a way in which it prevents the outflow of the heat of the liquids filled in them.
  • Conduction cannot take place as there will be no contact between any two layers.
  • Convection cannot take place as the top of the flask is closed with the cork or cap.
  • Radiation is prevented through the reflective surface of these layers inside and outside the flask. (See How to Change Transmission Fluid and Filter?)

5. What are the Uses of a Vacuum Flask?

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The thermos flask is a commercial name for the Vacuum flask. Thus apart from day-to-day uses of storing beverages at a constant temperature, vacuum flasks have other important uses. (See Morse Code Uses in Communication)

  • In laboratories and industries, vacuum flasks are used to hold liquefied gases like liquid nitrogen for processes where an extremely low temperature is required.
  • The insulation provided by a vacuum flask will help keep liquids at their liquid state even without cold or refrigeration equipment.
  • The vacuum flasks also help in storing certain types of rocket fuels.
  • The design of the flask is used in various experiments like optical experiments, chemical experiments, thermal experiments, etc.,
  • Thermos flasks are used during the shipping of medical vaccines as vaccines are sensitive to heat.
  • Machines like NMR and MRI machines are based on the use of double vacuum flasks.
  • In industries of oil and gas which require extensive pipelines and machinery at various temperatures, thermos flasks are used to keep the electronic tools and components insulated. (See How Is Gasoline Made From Oil?)

So how does a thermos work, is through preventing the three processes of conduction, convection, and radiation. And hence, these qualities of the thermos make them the containers that keep food hot for hours. (See What is a Chuckwagon?)

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