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Dry ice. a liquid nitrogen

Dewar vessels help to store a substance at a temperature that has a lower or higher value. One of the main qualities of such a device is its low thermal conductivity. Due to this, the temperature can maintain its original value. In addition, the activation of this factor is also facilitated by processes of various directions occurring in the substance itself.

Modern vessel design

Vessels are being made dewar vessels so ... Both glasses - both the one inside and the one outside, are made of heat-resistant aluminum. Sometimes stainless steel can be used as the main component. The main property of a substance for placing it in a vessel is specific gravity. Between the two glasses there is a jumper. It should be strong enough, but at the same time thin enough. It can be made from of stainless steel or from the most durable plastic (the latest trends).

Manufacturers are constantly faced with the question of ensuring a vacuum seal due to the existing fastening. To do this, the vessel that is outside is covered with a special substance - an adsorbent. Such a substance is able to absorb excess gases released inside the vessel. To reduce heat loss, the vessel is additionally covered with heat-insulating material. To reduce the possible convection process, a foam cylinder is attached to the lid, which overlaps the jumper, but does not completely do this. All those gases that have low pressure are pumped out of the vacuum region. The surface is carefully polished from the inside.

Helium Dewars

The use of helium for its use in vessel design is due to low heat losses. That's why this species The vessel is shielded with helium cooled with liquid nitrogen. For the screen, metals are used that conduct heat well. In such a Dewar vessel, two jumpers can be observed: one is made for liquid nitrogen, the other for helium. The helium jumper is also supplied with drain fittings, connectors for connecting a pressure gauge and a siphon. Such control methods allow you to build up a certain pressure and control the manipulations performed.

Scope of Dewar vessels

Any person uses Dewar vessels almost every day in his life, sometimes completely unaware of it. An ordinary thermos is a vessel model adapted for the preservation of tea, coffee and other drinks. Dewars are used for experimental research to help keep substances cool. Besides, this equipment allows you to leave unchanged biological samples for their use in medicine.

Dewar tanks

Tanks of various types are used to transport refrigerated substances over a distance. The principle of their manufacture is identical, only the volumes are increased compared to conventional vessels. The foundation that makesmobile dewar tankspossible to application - walls with a double bottom. The material for the manufacture of glasses is steel, and jumpers are made from it. Liquid nitrogen is used as a cooling medium; the tank can be shielded with a helium layer. Dewar tanks help to keep the qualities of the refrigerated substance in their original state.

Thermal insulation of Dewar vessels

Previously, two models for providing thermal insulation of the vessel were used: vacuum, and shielding of the vessel with helium, coupled with cooled nitrogen. Both models were very effective, but in both cases there could be very small some points that needed to be improved. In particular, with a possible gas leak and a violation of the integrity of the shell, it was almost impossible to detect it. The use of cryogenic liquids of various kinds makes it possible to increase safety in the use of the vessel. After all, in the case of too much loss of the original product, the vessel is able to explode due to the pressure difference between the internal and external environment.

Thermal insulation of pipelines for pumping nitrogen

Nitrogen is one of the substances that require constant monitoring during pumping and transportation. Therefore, thermal insulation for pipelines in contact with this gas must be appropriate. More oftenthermal insulation of pipelinestoday it is carried out in the form of a liquid ceramic material. A lot of silicone balls filled with oxygen, invisible to the eye, are constantly moving inside the liquid consistency. The basis for such a liquid are acrylic polymers, synthetic rubber, and inorganic elements. This combination contributes to greater flexibility, greater reliability of the material. Such liquid material is usually white in color. It dries quickly enough, forming the necessary protective film.

A new method of thermal insulation

Thanks to the technologies being put into operation (the use of liquid thermal insulation) for the transportation and storage of nitrogen and other substances, the production of Dewar vessels should also become much cheaper. At the same time, the benefits of using devices for practical purposes will increase markedly. This also applies to tanks and small vessels made on the same basis.

Fragment of a patent application

Physicists Karol Olszewski and Zygmunt Wroblewski used a glass box with double walls to store liquefied gases, with air evacuated from the interwall space. This container was developed by the German physicist Adolf Ferdinand Weinhold.

Device

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

Modern designs

Modern Dewar vessels are constructed somewhat differently. The inner and outer vessels are made of aluminum or stainless steel. The thermal conductivity of the material is not important, but strength and weight play a big role. The neck connects the inner and outer vessels. In dewars with a volume of up to 50 l, the inner vessel is attached only to the neck and it experiences great physical stress. It also has high requirements for thermal conductivity. Those. the neck should be strong, but thin. In ordinary vessels, the neck is made of stainless steel. In high-quality Dewar flasks, 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 covered 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 convection heat transfer, a foam plastic cylinder is attached to the Dewar lid, which does not tightly close the neck. The vacuum cavity is pumped out to a pressure of 10 -2 Pa. Silvering of internal surfaces was abandoned and replaced with polishing.

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

Helium Dewars

Diagram of a Dewar vessel for helium
1 - neck for filling nitrogen;
2 - head with fittings;
3 - neck of the helium container;
4 - container for liquid nitrogen;
5 - thermal screens;
6 - container for liquid helium;
7 - thermal insulation;
8 - adsorbent

Links

Specifications, nitrogen storage in a Dewar

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See what "Dewar vessels" are in other dictionaries:

- (named after J. Dewar) vessels with double walls, between which a vacuum is created [not less than 1.33 mN/m2 (10 5 mm Hg)], which ensures high thermal insulation of the substance inside the vessel. Heat transfer in D. with. almost happens...

Dewar vessel- Dewar vessels: a, b glass; into metal for liquid gases (nitrogen and helium). DEWAR VESSEL, a flask with double walls silvered on the inside, from the space between which air is pumped out. Thermal conductivity of a rarefied gas between the walls ... ... Illustrated Encyclopedic Dictionary

A flask with double walls silvered on the inside, from the space between which the air is pumped out. The thermal conductivity of the rarefied gas between the walls is so small that the temperature of the substances placed in the Dewar vessel remains constant for a long time ... encyclopedic Dictionary

Vessel with double walls, between which a vacuum of at least 1.33 mN/m² (10–5 mm Hg) is created, which provides high thermal insulation of the internal volume of the vessel. Proposed by the English physicist J. Dewar in 1898. The simplest Dewar vessel ... ... Encyclopedia of technology

- [in the name of the English. physicist and chemist J. Dewar (J. Dewar; 1842 1923)] a vessel with double walls, a vacuum is created between them, which provides high thermal insulation in the vessel inside the vessel. Small D. with. made of glass, vessels ... ... Big encyclopedic polytechnic dictionary

For liquid oxygen A Dewar vessel is a vessel intended for long-term storage of substances at high or low temperatures. Before being placed in the Dewar vessel, the substance must be heated or cooled. Constant temperature ... ... Wikipedia

VESSEL DEWAR- A special refrigerating vessel for freezing and storing sperm of producers in liquid nitrogen. It is a double-walled container made of aluminum alloys or stainless steel. A special thermal insulation is placed between the walls. For increase … Terms and definitions used in breeding, genetics and reproduction of farm animals

- (from Cryo... and Greek states standing, motionless) A thermostat in which the working unit or the object under study is maintained at temperatures below 120 K (cryogenic temperatures) due to an external source of cold. Usually as... Great Soviet Encyclopedia

Cryogenic temperatures, usually temperatures below the boiling point of liquid air (about 80 K). Such temperatures are usually counted from absolute zero (See Absolute Zero) temperature (273.15 ° C, or 0 K) and expressed in kelvins ... ... Great Soviet Encyclopedia

In 1879, the German physicist A. Weinhold was puzzled by a purely scientific problem: how to store liquid or even solid hydrogen with a melting point as low as -259.2 ° C in laboratories. What was needed was a vessel that could maintain such a low temperature even in a warm room. The exit has been found. The scientist came up with the idea to connect two thin-walled glass vessels, placing one inside the other, hermetically solder the necks, and pump out air from the space between them. Thus, the vacuum kept the temperature of the inner container, not allowing it to heat up or cool down (the usual window panes). Being also an experienced glass blower, the physicist easily described the result in detail in his book “Demonstration Experiments in Physics”, modestly calling the invention the “Weinhold bottle”. A few years later, his Scottish colleague James Dewar improved the product by silvering the inner walls of the vessel to better maintain temperature. And the "bottle" turns into a "Dewar vessel".

But the improvements didn't end there. German glassblower Burger, who for a long time produced flasks for laboratories, noted that the Dewar vessel can be useful not only in science, but also in everyday life.

In 1903, Burger slightly modified the Scot's vacuum vessel, dressing the fragile glass in a metal shell, providing it with a functional cup-lid, and was the first of the three developers to guess to patent the invention. Soon a competition was announced for the best name for novelties. The Germans actively proposed various intricate names for the vessel. However, the winner was a resident of Munich, who remembered the Greek word therme (hot). So a thermo-vessel, exactly like the company that started its production got their name. In 1904, the German company THERMOS GMBH began the serial production of Dewar vessels, from that moment referred to as thermoses.

Naturally, the creator of the thermos, James Dewar, tried to prove the rights to the invention, which by that time had already brought serious income. Unfortunately, the scientist did not achieve justice, and Reinhold Burger remained the only developer indicated in the patent.

More than a hundred years have passed since then. Now you can choose a thermos of any capacity and color, in a metal, plastic and even glass case. And, for example, in Soviet time practically in each family there was a large tin thermos of red or blue color, decorated with flowers or picture rising sun. Bright and shiny, in the Soviet kitchen it was kept in plain sight as a piece of furniture. German thermoses did not reach the Union, but you could easily buy Chinese equivalent. Most of the thermoses brought to the country were produced at the Beijing Deer factory. In fact, foreign company names are usually transcribed rather than translated, but Olen decided to leave its Chinese name, entering the Western market as Bejiing Deer (Beijing deer). Thus, a tin Chinese with a German name entered our lives.

By and large, the design of the thermos has not changed since then, with the exception of a small but very important detail - corks. She, unlike the top cover-cup, did not screw. The fact is that the inner vessel of the Chinese thermos consisted of glass and had no thread. So only a lid-plug, usually wooden, was used. Naturally, such a vessel could not be turned over, which is not always possible in nature or on long journeys.

Now there is a huge variety of brands and varieties of thermoses: for food, drinks, thermo mugs. In a word, progress does not stand still. However, for many, this is not just an object, but a warm reminder of pleasant events: a trip to nature with friends, a long journey or a winter walk.