Dewar vessel

The first container for storing liquefied gases was developed in 1881 by the German physicist A.F. Weinhold . It was a glass box with double walls with air evacuated from the inter-wall space and was used by physicists K. Olshevsky and S. Vrublevsky to store liquid oxygen ^{[1] [2]} .

In 1892, Scottish physicist and chemist Sir James Dewar refined Weinhold’s glass box, turning it into a double-walled narrow- necked flask to reduce the evaporation of liquid. The interwall space is silvered and air is pumped out of it. Dewar first demonstrated his vessel to an audience at a public lecture on January 20, 1893 ^[3] . Dewar hung this entire fragile structure on springs in a metal casing. Thanks to his development, Dewar was the first to obtain and retain liquid ( 1898 ) ^[4] and even tried to obtain solid ( 1899 ) hydrogen ^[5] .

The first Dewar vessels for commercial use were produced in 1904 when the German Thermos GmbH thermos company was founded.

The original Dewar vessel was a glass flask with double walls, from the space between which air was pumped out . To reduce the radiation loss , both inner surfaces of the flask were coated with a reflective layer. Dewar used silver as a reflective coating. A similar design is used in modern cheap household thermoses.

Modern designs

Modern Dewar vessels are structurally made somewhat differently. The inner and outer vessels are made of aluminum or stainless steel . The thermal conductivity of the material is not important, and strength and weight play a large role. The neck connects the inner and outer vessels. In dewar with a volume of up to 50 l, the inner vessel is mounted only on the neck and it experiences great mechanical stress. It also has high thermal conductivity requirements. That is, the neck should be strong, but thin. In ordinary vessels, the neck is made of stainless steel. In high-quality Dewar vessels, the neck is made of durable reinforced plastic. This raises the problem of vacuum tight fastening of metal and plastic. Outside, the inner vessel is coated with an adsorbent , which, when cooled, absorbs residual gases from the vacuum cavity. To reduce heat loss, the inner vessel is covered with additional thermal insulation. To reduce the convection heat transfer, a foam cylinder is attached to the dewar cover, which tightly closes the neck. The vacuum cavity is pumped out to a pressure of 10 ⁻² Pa. They refused silvering of internal surfaces and replaced it with polishing.

Modern Dewar vessels have low evaporation losses: from 1.5% per day for large tanks, up to 5% per day for small volumes.

Dewar helium vessels

Helium has a very low heat of vaporization . Therefore, to reduce heat loss in helium dewar, thermal screens cooled by liquid nitrogen are used . Screens are made of materials that conduct heat well ( copper ). Such a Dewar vessel has two necks: for liquid nitrogen and helium . The helium neck is equipped with special fittings for gas discharge, siphon , pressure gauge , valve connection. The helium dewar cannot be tilted; it must always be in an upright position.

With the development of multilayer screen-vacuum thermal insulation technology, proposals for helium Dewar vessels appeared in the market, which do not use liquid nitrogen cooling. According to the manufacturers, in such Dewar vessels the evaporation loss is 1% per day for 100 liter containers.

• To preserve the temperature of food and drinks , Dewar household vessels - thermoses are used .
• In laboratories and in industry, a dewar vessel is used to store cryoliquids , most often liquid nitrogen .
• In medicine and veterinary medicine, special Dewar vessels are used for long-term storage of biological materials at low temperatures.
• In geophysics, electronic components and crystals are placed in Dewar vessels when working in hot wells (from 400K).
• In astronautics. The detector of the NICMOS instrument mounted on the Hubble Space Telescope was placed in a Dewar vessel using solid nitrogen as a refrigerant.

• Thermos
• Cryogenics
• Cryostat

• Burger, R., US Patent 872,795 , “ Double walled vessel with a space for a vacuum between the walls ”, December 3, 1907.
• Sivukhin D.V. General course of physics. - M .: Nauka , 1975 .-- T. II. Thermodynamics and molecular physics. - 519 p.

• Technical Specifications of Dewar Vessels for Nitrogen Storage
• Safety Instructions for Working with Liquid Nitrogen and Dewar Vessels
• Dewar vessel explosion when pouring liquid nitrogen (TB violation)