Vacuum flask

Thermos

Dewargefäß Deutsches Museum

Vacuum Dewar Flask

Liquid nitrogen tank

Gustav R. Paalen, Double Welled Vessel 1909

Termos, Thermofix original - Nordiska museet - NMA.0097258

Vacuum flask, also known as a Dewar flask, Dewar bottle, or thermos, is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings. Invented by Scottish scientist Sir James Dewar in 1892, the vacuum flask consists of two flasks, placed one within the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which significantly reduces heat transfer by conduction or convection.

Design and Function

A vacuum flask has two primary components: an inner chamber and an outer chamber. The inner chamber holds the substance to be kept hot or cold, while the outer chamber forms the protective casing. The space between these two chambers is evacuated to create a vacuum, a region with very few air molecules. This vacuum acts as an excellent insulator because heat transfer through conduction or convection is greatly reduced. Heat transfer by radiation is also minimized through the use of reflective coatings on the surfaces facing the vacuum.

To further enhance its insulating properties, the flask is usually made from materials that are poor conductors of heat, such as glass or plastic for the inner chamber, and metals or plastic for the outer chamber. The opening of the flask is typically sealed with a cork or plastic stopper to prevent heat transfer through convection.

Applications

Vacuum flasks are widely used to keep beverages hot or cold for extended periods. They are a common sight in various settings, from outdoor activities like camping to daily use in homes and offices. Beyond domestic use, vacuum flasks have specialized applications in science and industry, where they are used to store liquid nitrogen and other cryogenic liquids. Their insulating properties are crucial for the storage and transport of materials that require strict temperature control.

History

The vacuum flask was invented by Sir James Dewar in 1892 as a result of his research in the field of cryogenics. Dewar needed a storage vessel that could maintain a low temperature for his experiments with liquid gases. He created the first vacuum flask by placing one glass bottle inside another and pumping out the air between them to create a vacuum. Although Dewar did not patent his invention, a German company, Thermos GmbH, commercialized the technology and started selling vacuum flasks to the public in 1904.

Environmental Impact

Vacuum flasks can have a positive environmental impact by reducing the need for disposable containers for beverages. By using a reusable vacuum flask, individuals can decrease the amount of waste generated from single-use cups and bottles. Additionally, by keeping beverages at the desired temperature for longer, vacuum flasks can reduce the energy consumption associated with reheating drinks.

See Also

• Insulation
• Cryogenics
• Thermal conduction
• Convection
• Radiation

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