The cryogenic storage dewar is one of the very earliest cryogenic applications. This practical storage vessel is typical in virtually all cryogenic industries and is used for storing, transporting, and applying cryogenic liquids.
In this blog, we look at the functioning and application of the cryogenic storage dewar. We explain how a dewar works, what types of dewars there are, and why many cryogenic infrastructures include a dewar.
What is a cryogenic storage dewar?
As we covered in our recent blog on cryogenic applications, the dewar has been used for over a century. As early as 1892, not long after the very first gases were liquefied, James Dewar developed this popular storage vessel to safely store cryogenic liquids such as liquid nitrogen and liquid helium.
A cryogenic storage dewar is, simply put, a highly insulated vessel specifically designed to hold materials at extremely low temperatures.
A vacuum is often used to insulate a dewar. Vacuum insulation is achieved by pumping out all the air between the double wall enclosing the entire dewar. The vacuum stops the movement of molecules, making heat transfer impossible.
Various types of cryogenic storage dewars
There are various types of dewars. While, in theory, a dewar can be fabricated in almost any shape, the three types below are perhaps the most well-known:
Bottle-shaped dewars (vacuum flask)
First off, bottle-shaped dewars. These vacuum-insulated vessels are used for cryogenic liquid storage and cryogenic sample storage. With this type, the screw cap is opened, and the sample is placed in the dewar for cryopreservation. We will come back to this again in detail later in this blog.
Dewars with a wide opening (open top)
Second, dewars with a wide opening at the top. This design is ideal for applications that cannot be performed with a bottle-shaped dewar. Examples include the embedding of small vials or the rapid freezing of tissues.
In addition to the above relatively simple dewars, there are also more sophisticated variants. One of these is the self-pressurizing dewar.
When a dewar is connected to an application, it can be essential that the cryogenic fluid reaches the application at a specific pressure. Mainly in laboratories, this can be extremely important.
When a higher pressure is required than the production capacity of a standard dewar, a self-pressurizing dewar is used. This particular dewar contains a special valve through which the cryogenic liquid passes through a boiling coil. This increases the pressure in the dewar, forcing the liquid gas out of the dewar with adequate pressure.
Cryogenic storage dewars not only come in different shapes and sizes but also in different materials. The exterior of a dewar is often made of stainless steel, but the two walls of the vacuum insulation can be made from either glass or stainless steel.
There are also dewars made of entirely different materials, such as foam. These relatively small dewars are lighter, cheaper, and can, for example, be used to rapidly cool samples. For long-term storage, a dewar with vacuum insulation is more efficient. After all, vacuum insulation offers the highest grade of insulation of all available insulators.
Application of cryogenic storage dewars
In the previous sections, we emphasized the importance of cryogenic storage dewars for storing biological samples. This, however, is not the only application of the dewar.
Among our customers, we regularly see the following three applications of a dewar:
Temporary storage tank for new sites
Most users of cryogenic liquids have a large storage tank on-site. This tank is placed by a gas supplier and is connected by vacuum-insulated piping to, for example, a cryogenic freezer, a nitrogen filling station, a freeze dryer, or other cryogenic applications.
However, dewars are usually temporarily used when the application is located where a fixed storage tank is not yet installed. Although these are often smaller than regular storage tanks, they allow safely storing liquid gases on-site.
For example, with flexible vacuum-insulated transfer lines and easy-to-install Johnston couplings, an application can be temporarily connected to a dewar until the final tank and associated infrastructure are installed.
Transportation to another room or department
Even when a location is equipped with a fixed storage tank, it may be required to carry small quantities of cryogenic liquid from this tank to a department or workplace. This is another application for which cryogenic storage dewars are used.
Many hospitals and laboratories use small dewars (wheeled or not), which are easy to move around the building. Employees transport small quantities of liquid gas from the central storage tank or a nitrogen filling station in a dewar to their workstations.
Finally, an application we’ve mentioned before: cryopreservation. Cryopreservation is a widely used method within the medical and pharmaceutical industries, where biological material or chemical components are preserved using cryogenic fluids. In most cases, liquid nitrogen (-196°C) is used as the coolant; however, this depends on the material that needs to be cooled.
Cryopreservation takes place in special rooms called biobanks. These rooms are full of dewars in which the material to be preserved is stored for long periods. Some examples of materials preserved by cryopreservation include blood cells, stem cells, eggs, embryos, plant germplasm, and medications.