A vacuum flask, also known as a thermos flask or a Dewar flask, is a double-walled container designed to keep liquids hot or cold for extended periods of time. It is a widely used piece of equipment in everyday life, from outdoor activities such as camping to office work and even medical settings.
The vacuum flask has two walls, with the inner one made of glass or steel and the outer one providing insulation; the vacuum prevents heat transfer.
The vacuum flask operates on the principle of thermodynamics. Heat transfer occurs in three ways: conduction, convection, and radiation. In a vacuum flask, the vacuum or insulating layer reduces the effects of conduction and convection, while the reflective surface of the vacuum jacket reduces the effects of radiation. This means that the heat of the liquid is trapped inside the flask, keeping it hot or cold for longer periods of time.
Vacuum flasks are available in a range of sizes and shapes, from small ones that hold a single cup of liquid to large ones that can hold several liters. They come with different features, such as screw-on or push-button lids, handles, and spouts. Some vacuum flasks are designed for specific purposes, such as those with narrow openings for sipping or those with wide openings for pouring.
The vacuum flask is an essential item that has become a staple in many aspects of everyday life. Its ability to keep liquids hot or cold for extended periods of time is due to the thermodynamics principles of heat transfer, making it a reliable and convenient way to enjoy hot or cold drinks while on the go.