Vacuum flask

A vacuum flask (also known as a Dewar flask, Dewar bottle or thermos) is a special container that helps keep things hot or cold for longer.

It works by slowing down how quickly the temperature inside changes. This is done by trying to stop heat from moving in or out.

The vacuum flask was invented by James Dewar in 1892. It has two bottles, one inside the other, with a space in between. This space has very little air, which helps keep the temperature inside steady.

Vacuum flasks are used at home to keep drinks or food hot or cold for a long time. They can also be used for thermal cooking and many other jobs in factories and businesses.

History

The vacuum flask was invented by Scottish scientist James Dewar in 1892. He made it to study very cold temperatures, called cryogenics. Dewar built a flask with two layers and removed the air between them. This helped keep the contents at a steady temperature. He did not patent his invention, so others could use new materials like glass and aluminium to improve it.

Soon after, two German glassblowers, Reinhold Burger and Albert Aschenbrenner, found that this flask could keep drinks cold or hot for longer. They made a stronger version for everyday use and named it Thermos. Although Dewar tried to claim ownership, he lost a court case to them. The design was later improved by Gustav Robert Paalen, who made many different types for homes and sold them widely. The American Thermos Bottle Company began making these flasks in large numbers in Norwich, CT, making them cheaper and more available. Over time, many companies made similar products to keep drinks hot or cold, such as for coffee or camping trips.

The name "thermos" became commonly used for all vacuum flasks. As of 2023^[update], Thermos and THERMOS are still trademarks in some countries, including the United States, but the lowercase "thermos" was declared a genericized trademark in the United States in 1963.

Design

A vacuum flask has two containers, one inside the other and joined at the top. The space between them has very little air, which helps keep things hot or cold for longer. Heat can still escape through the opening at the top, so flasks are usually made from metal, special glass, foam, or plastic and closed with cork or plastic lids. They are often used to keep food or drinks warm or cool when you are traveling.

Very large flasks sometimes need extra support for the inner container, using special pieces called spacers. These can affect how well the flask keeps things hot or cold. Some special flasks used in machines like NMR and MRI have two layers of vacuum to protect very cold liquids. Other designs also help reduce evaporation from the flask.

Research and industry

See also: Cryogenic storage dewar

In labs and factories, vacuum flasks are used to store very cold liquids, like liquid nitrogen, which helps keep things frozen for experiments. These flasks can also hold gases that are very cold, such as oxygen and nitrogen. Because they are well-insulated, the liquid inside stays cold for a long time without needing extra cooling.

Vacuum flasks are also used to keep precise electrical equipment at the right temperature. They help make sure that special tools used to measure electricity stay accurate. One famous example is a device made by Guildline Instruments in Canada, which used a vacuum flask to keep its tools working perfectly.

These flasks are even used in space! NASA used them to store rocket fuel in the 1960s and 1970s. They are also used to protect medicines, like vaccines, from getting too warm during shipping. In the oil and gas industry, they help keep sensitive tools working in very hot places.

Safety

Vacuum flasks can break if not handled carefully. Glass ones might shatter without warning. Small scratches or chips can make this more likely, especially when the flask is filled quickly with very hot or very cold liquid. To help prevent this, it is important to prepare glass flasks properly before use.

When storing very cold materials, some vacuum flasks are pressurized and could burst if special safety parts are not used. Because the inside and outside of the flask can heat up or cool down at different speeds, this can sometimes cause the flask to break apart. Special joints are often used in some flasks to help prevent this problem.