The Dewar flask is the grandfather of modern thermoses. Today there are no problems with saving necessary products for a long time at a certain temperature. The reason for the invention of such a vessel was that physicists did not have the opportunity to preserve gases in a liquid state for some time. The Dewar flask for liquid nitrogen was precisely the invention that successfully solved the problem. And, as always happens, a godsend for scientific works found its application in everyday life.
Story
The so-called Dewar flask dates back to 1881. German scientist Adolf Ferdinand Weinhold developed the very first container that was used to store liquefied gas.
It was a glass box with double walls. A special feature of the design was that air was pumped out from the interwall space. Liquid oxygen could be stored in such a vessel. The inventor called the vessel “Weinhold bottle.”
In 1892, the Scottish chemist and physicist Sir James Dewar made some improvements to A. F. Weinhold's design. The glass box changed shape and became a flask with a narrow neck, which significantly reduced the evaporation of liquid. In addition, according to Dewar's instructions, the interstitial space was silvered. For the first time, not only liquid, but also solid hydrogen was obtained and stored.
The first demonstration took place at a public lecture in January 1893, and mass production of the vessels began in 1904. Thermos GmbH (Germany) was founded for the manufacture of thermos flasks, and it took up the implementation of the invention for commercial purposes.
Operating principle
How does a Dewar flask work? The design of the device is striking in its ingenious simplicity: a glass or metal flask with double walls, between which air is evacuated. This system significantly reduces the thermal conductivity of the walls.
The remaining very small amount of air molecules transfers the temperature to the contents of the Dewar flask environment. This residual thermal conductivity provokes constant and gradual evaporation of the liquid gas.
This, in turn, leads to an increase in pressure inside the container. To avoid an inevitable explosion, the device is equipped with a safety valve or is not tightly closed. A loosely closed plug has little effect on the evaporation of liquid nitrogen. Heat transfer from bottom to top occurs slowly, and the area of the hole in the vessel is negligible.
Thus, the gas is gradually released. The loss of the substance is insignificant, for example, one kilogram of liquid air will lose only 4 grams during 10 days of storage.
This device makes it possible to store and transport gas in a liquid state for a long time, which is very important for modern industry.
Models
In many industries, Dewar flasks are used for various purposes. There are several models:
- series X, XT, LD - aluminum, fiberglass neck, used for transportation and storage of liquid nitrogen and biomaterials;
- series SK, SDP - with a fiberglass neck, made of aluminum, used for transportation and storage of small amounts of liquid nitrogen;
- SDS series - aluminum, fiberglass neck used for transportation and storage of biomaterials;
- vertical (volume 28-660 liters) - made of stainless steel, used for transporting and storing nitrous oxide, liquid nitrogen, carbon dioxide, argon, oxygen;
- horizontal - made of stainless steel, used for storing liquid nitrogen.
In addition, the production of huge railway and road tanks has been mastered. There are also specially equipped ships transporting large quantities of liquefied gas.
Application
Dewar flasks are widely used in modern industries. Most often the device is used:
- in everyday life - for long-term storage of drinks and food (thermoses);
- in industry, laboratories - for preserving liquid nitrogen and other cryofluids;
- in veterinary medicine and medicine - for storing biological material;
- in geophysics - for work in hot wells (crystals and electronic components are placed in a vessel).
Price
Currently, the market offers a wide variety of brands and types of thermoses. Small household products are used for food or liquids (tea, coffee). The price, depending on the volume, material and brand of the manufacturer, can range from $5 to $50.
The cost of those vessels that are used in industrial scale and are called a Dewar flask. The price is determined by the volume and quality of workmanship. A good, large-volume device can cost several hundred dollars:
- model X-40SP (Kharkov Transport Equipment Plant, Ukraine) - $650;
- model L2050 (Cryo Diffusion, France) - $1050;
- model XT-3 (Taylor-Wharton, Slovakia) - $220.
Tanks, road or rail, for transporting cryogenic liquids cost tens of thousands of dollars.
In 1879, the German physicist A. Weinhold was puzzled by a purely scientific problem: how to store liquid or even solid hydrogen in laboratories with a melting point of as much as -259.2 ° C. A vessel was needed that would maintain such a low temperature even in a warm room. A solution was found. The scientist came up with the idea of connecting two thin-walled glass vessels, placing one inside the other, soldering the necks hermetically, and pumping out the air from the space between them. Thus, the vacuum maintained the temperature of the internal container, not allowing it to heat up or cool down (the same principle applies to conventional window glazing). Being also an experienced glassblower, the physicist easily described the result in detail in his book “Demonstration Experiments in Physics,” modestly calling the invention “Weinhold’s bottle.” A few years later, his Scottish colleague James Dewar improved the product by silvering the inner walls of the vessel to better preserve the temperature. And the “bottle” turns into a “Dewar flask”.
But the improvements didn't stop there. German glassblower Burger, for a long time who produced flasks for laboratories, noted that the Dewar flask can be useful not only in science, but also in everyday life.
In 1903, Burger slightly modified the Scotsman's vacuum vessel, putting the fragile glass in a metal shell, providing it with a functional cup lid, and the first of the three developers thought of patenting the invention. Soon a competition was announced for best name For new items. 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 thermal vessel, just like the company that produced it found your name. In 1904, the German company THERMOS GMBH began serial production of Dewar vessels, from that moment on referred to only as thermoses.
Naturally, the creator of the thermos, James Dewar, tried to prove the rights to the invention, which by that time was already generating serious income. Unfortunately, the scientist never achieved justice; Reinhold Burger remained the only developer named 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, red or blue, decorated with flowers or an image of the 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 it was easy to buy a Chinese equivalent. Most of the thermoses brought into the country were produced at the Beijing Olen factory. Actually foreign names companies usually transcribe rather than translate, 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, since those times the design of the thermos has not changed, with the exception of a small, but very important detail- traffic jams. It, unlike the top cup lid, did not screw down. The fact is that the inner vessel of the Chinese thermos consisted of glass and had no thread. So, only a plug lid was used, usually a wooden one. Naturally, such a vessel could not be turned over, which is not always possible in nature or on long trips.
Now there is a huge variety of brands and varieties of thermoses: for food, drinks, thermal mugs. In a word, progress does not stand still. However, for many it 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.
Video What is a thermos?
For their needs, not everyone has an idea about their structure. Now we will tell you how this container is designed and why, while in it, cryogenic liquids retain their properties.
Prototype of a modern vessel
The first tank for storing cryogenic liquids was invented at the end of the nineteenth century in Germany. Then it was a glass box with double walls, between which a vacuum was created. The Scottish scientist J. Dewar modified the invention, giving it the shape of a flask with a narrow neck.
This design was not chosen by chance - the narrow neck prevents the rapid evaporation of cryogenic liquids, and the vacuum in the interwall space helps maintain the specified temperature of the substances. The walls on the inside were silver plated, which provided additional thermal insulation. With the advent of new technologies, the design was improved until we got the product we use now.
Design of modern Dewar flasks
Modern products that we are accustomed to are somewhat different from their predecessors. While the first Dewar flasks were made of glass, they are now made of aluminum or stainless steel. Important role When choosing a material, strength and weight play a role.
The main components of a Dewar flask:
- external and internal vessel;
- neck;
- lid;
- adsorbent for the interwall space.
The external and internal vessels are connected at the neck. From the space between them, air is pumped out to a pressure of 10 −2 Pa (a vacuum is created). The walls of the inner vessel are coated on the outside with an adsorbent substance. This was done to remove residual gases from the vacuum space.
The neck connects both parts of the vessel. Depending on the model, the neck can be narrow or quite wide (up to 210 mm in diameter). It is made of reinforced plastic; to reduce the cost of production, stainless steel can be used.
The lid of the vessel allows you to tightly (but not hermetically) close the neck. A foam cylinder is additionally attached to it, which closes it and helps bleed off excess liquid nitrogen. The silvering of the vessel walls was abandoned, replaced by polishing.
If you are looking for Dewar flasks with high technical characteristics, we recommend ordering them in our store. All products come with a guarantee, and a large selection of products will allow you to choose the best option.
HVM, an Italian company headquartered in Livorno, has been developing and producing a wide range of cryogenic Dewar vessels for more than 20 years with different operating pressures, different gas and liquid removal systems, vertical and horizontal, palletized controls, etc. The company's products are used for storing and transporting gases at low temperatures. Areas of use:
- industrial
- scientific
- food
- fish farming
- cryobiology
- livestock farming
- pest control
Also, the company has developed oxygen therapy units (stationary “OXY-BLU” and compact “OXY-LIGHT”).
All products meet European ADR and TPED requirements (Directive 2010/35/UE). Westmedgroup is the official supplier of cryogenic vessels to Russian market medical equipment.
A Dewar flask is a vessel designed for long-term storage of substances at high or low temperatures. A constant temperature is maintained by passive methods, due to good thermal insulation and/or processes in the stored substance (for example, boiling). This is the main difference between a Dewar vessel and thermostats and cryostats.
First storage container liquefied gases was developed in 1881 by the German physicist A.F. Weinhold. It was a glass box with double walls with air pumped out from the interwall space and was used by physicists K. Olshevsky and S. Vrublevsky for storing liquid oxygen.
Scottish physicist Sir James Dewar improved the Weinhold glass box in 1892, turning it into a double-walled flask with a narrow neck to reduce evaporation of liquid. The interwall space is silvered and air is evacuated from it. Dewar suspended this entire fragile structure on springs in a metal casing. Thanks to his development, Dewar was the first to obtain and store liquid (1898) and even solid (1899) hydrogen.
The first Dewar flasks for commercial use were produced in 1904, when the German thermos flask manufacturer Thermos GmbH was founded. In laboratories and industry, a Dewar flask is used to store cryofluids, 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).
Cryostats vary
by the type of refrigerant used (nitrogen, helium, hydrogen, etc.);
by the material from which they are made (glass, metal, plastic);
for its intended purpose (for radio engineering, optical, medical and other research, for superconducting magnets, radiation receivers, etc.).
The advantage of using vertical cryogenic tanks is the space savings compared to horizontal cryogenic tanks. However, vertical tanks require the development of a project for their installation and registration with Rostechnadzor, unlike transport cryogenic tanks.
The thermos was invented by three people over a quarter of a century. In 1879, physicist Professor A. Weinold proposed using a double-walled glass vessel with a vacuum between the walls to preserve liquid gases. In 1890, English chemist Professor James Dewar improved the “Weinhold bottle” by silvering the walls, which reduced heat leakage through the walls. Finally, in 1904, the Berlin glassblower R. Burger added a protective shell to the Dewar flask and began selling it as a thermos for hot coffee or broth.
The Dewar vessel is a “vessel in a vessel” tank, the interwall space of which is filled with multilayer insulation (aluminum foil ADI-M-0.011 and glass paper - glass veil EVTI-7) and the air during manufacture is evacuated to a residual pressure of 10 (-4) mmHg. Art. To maintain a deep vacuum, an adsorbent and a hydrogen absorber are located in the interwall space. The material of the vessel is aluminum alloy AMts, thanks to which the temperature in the upper zone of the Dewar vessel does not rise above minus 170 degrees Celsius even with 5 kg in it. (12%) liquid nitrogen.
Currently, cryogenic equipment is being commercially produced ( Greek Krios- cold, genos- birth) of different types and brands: industrial Dewar vessels - SDP: SDP-5, SDP-10, SDP-16, SDP-25, SDP-40, etc. (the number indicates the capacity of the vessel in liters); SD - agricultural: SDS-5, SDS-20, SDS-30, X-30 (Kharkov-30), etc.; stationary storage facilities – HSZHA, KV-6202, KhB-0.5 (for 500 l.), KhB-0.2 (for 240 l.), etc.
The most important characteristic of the Dewar Vessel is the period of complete evaporation of liquid nitrogen, which for all SDP and SDS is 30-35 days, and in vessels of the old AT-6 type - up to 20 days. The volatility of liquid nitrogen from SDP-5 to SDP-40 ranges from 10 to 24 g/h (4.8-1.8% per day!), in SDS-20, SDS-35, SDS-50, respectively, 10.12, 14 g/h.
Dewar vessels of the new generation “SDS-35M” and SDS-6M – have more advanced multi-layer thermal insulation and high vacuum; the inner and outer layers of aluminum alloy are connected by a fiberglass neck, while the time for complete evaporation of liquid nitrogen reaches 300 and 48 days, respectively, and the evaporation of liquid nitrogen is 3.9 and 4.6 g/hour. (See Fig. Diagram of a Dewar vessel).
Liquid nitrogen is a colorless liquid, appearance resembles water. Its boiling point is -196 °C, specific gravity 0.804 kg/l, heat of evaporation -47.7 kcal/kg. Of all the cryogenic liquids obtained by liquefying atmospheric air (liquid air, liquid oxygen -183 °C), liquid nitrogen is the least dangerous and chemically inert. Evaporating, it turns into nitrogen gas, which is colorless, odorless, non-flammable, its specific gravity is 1.16 kg/m3, molecular weight 28; V atmospheric air it is contained in an amount of 79%. With prolonged inhalation of air with a high nitrogen content (decrease in oxygen content less than 16%), a person experiences a headache, and with high concentrations of nitrogen (for example, pouring nitrogen from a fallen Dewar flask), a fainting state occurs. Therefore, in rooms where they work with liquid nitrogen, there must be forced ventilation. At the point, Dewar vessels are stored in a playpen, in a specially fenced off place or laboratory, at such a distance from a window or door that a hose for filling with liquid nitrogen can reach it.
In the event of a fall, impact, or sudden shock, a disruption of the connection between the internal and external vessels may occur, since they are connected only in the neck area, which is accompanied by a loss of vacuum, therefore, during transportation, it is necessary to securely secure the Dewar Vessel in the body of the vehicle. The first sign of loss of vacuum is icing, the appearance of frost - the formation of a “snow coat” in the area of the neck of the casing of the Dewar Vessel; evaporation of the liquid occurs very quickly. It is strictly forbidden to leave such Dewar flasks for heating in a room where people may be present, since an increase in pressure in the interwall space can lead to an explosion. Dewar flasks that have lost vacuum are heated for at least three days in an isolated room, and then sent to the manufacturer for repair.
Features of the operation of Dewar Vessels is that the operator must regularly determine the level of liquid nitrogen in them. The first measurement is made a week after topping up, the second - a week after the first. The measurement results are recorded in a journal. For conventional Dewars, it is necessary to take a third measurement, during the third week after refilling, and it is necessary to record the ambient temperature and how many times the Dewar is opened. The level of liquid nitrogen can be determined with a special metal probe - a measuring ruler: it is lowered into the Dewar Vessel to the bottom and held for 15-20 seconds, removed - the frozen zone will show the amount of nitrogen in the Dewar Vessel.
