The thermo flasks we use so much during sport or for our summer trips use the vacuum principle to keep drinks hot or cold for extended periods. How does it work?
The secret lies in the structure of the thermo flasks, which has a vacuum gap between two ‘walls’.
This is because a vacuum is an excellent thermal insulator. In an environment without pressure, there are very few air molecules and without these molecules, heat transfer through molecular collisions is drastically reduced.
Conduction and convection require a material medium through which heat molecules can travel. The absence (or near absence) of matter and fluid means that heat cannot easily transfer from one wall of the flask to another.
To maximise this feature of the vacuum, thermo flasks often include reflective coatings on the inside of the walls (e.g. aluminium) that help reflect thermal radiation (heat) back into the drink, further helping to maintain a constant internal temperature.
For hot drinks, this system prevents heat loss from the inside to the outside. For cold drinks, it does not allow heat to enter from the outside.
Once again, vacuum science is able to influence small and big issues in everyday life!
