Double-Walled Structure: A thermos flask, also known as a vacuum flask, consists of two layers of glass or stainless steel with a small gap between them. This creates a double-walled structure.
Evacuation of Air: During the manufacturing process, the air is removed from the gap between the two walls. This is done by heating the flask and then allowing it to cool, which creates a vacuum. The remaining air is then pumped out using a vacuum pump.
Vacuum Insulation: The vacuum created between the two walls acts as an excellent insulator. Since there are no air molecules to transfer heat through conduction or convection, heat transfer is significantly reduced. This is what allows the thermos flask to keep its contents hot or cold for an extended period.
Silver Coating: To further enhance insulation, the inner surface of the outer wall and the outer surface of the inner wall are often coated with a reflective material, usually silver. This coating helps to reduce heat transfer through radiation.
By combining the vacuum insulation with the silver coating, thermos flasks effectively minimize heat transfer, allowing them to maintain the temperature of their contents for several hours.
