Cryogenic storage dewars and EM waves

In summary: Indeed, if you cut a dewar in half you will find that the vacuum space is not actually empty but includes multiple layers of metal covered films ("space blanket").The vacuum between the metal layers of a dewar acts as a thermal insulator, reducing the rate at which the contents boil away.
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I was researching cryogenic storage dewars and read that, "All dewars have walls constructed from two or more layers, with a high vacuum maintained between the layers. This provides very good thermal insulation between the interior and exterior of the dewar, which reduces the rate at which the contents boil away."

I thought that heat was a type of EM wave (infrared), and as I know EM waves can travel through a vacuum. So how does a vacuum provide good thermal insulation?
 
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Conduction (and convection, if possible) is far more efficient than thermal radiation. Making the walls of the vacuum reflective in the infrared helps, too.
 
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Got it! Thanks:biggrin:
 
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Indeed, if you cut a dewar in half you will find that the vacuum space is not actually empty but includes multiple layers of metal covered films ("space blanket").
While it is certainly true that convection and conduction typically will dominate heat transport, radiation is still very much something you need to consider when designing a dewar (or, more generally, a cryostat).
This is also one reason the inside of cryostats are typically very shiny (often gold plated)
 
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mfb said:
more efficient than thermal radiation.
"Break even" is around 500 K; higher temperatures "run-away" as T4.
 
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f95toli said:
Indeed, if you cut a dewar in half you will find that the vacuum space is not actually empty but includes multiple layers of metal covered films ("space blanket").
I used to work in a small cryogenics factory. I'd tell everyone I was 'a cryogenics technician specialising in installation of radiation shielding', since it sounded so much better than 'wrapping pipes in aluminium foil'.
 
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f95toli said:
Indeed, if you cut a dewar in half you will find that the vacuum space is not actually empty but includes multiple layers of metal covered films ("space blanket").
That's the flashy modern stuff. The Vacuum Flasks I used to keep my tea in were blown glass with internal silvering. I'm amazed at just how good the domestic stainless steel flasks are, compared with the old 'Thermos'. And you can drop them too!
 
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1. What is a cryogenic storage dewar?

A cryogenic storage dewar is a specialized container used for storing materials at extremely low temperatures, typically below -150°C. It is designed to keep the contents at a constant temperature by minimizing heat transfer from the surrounding environment.

2. How does a cryogenic storage dewar work?

A cryogenic storage dewar works by using a combination of vacuum insulation and reflective coatings to minimize heat transfer. The vacuum space between the inner and outer walls of the dewar reduces conduction and convection, while the reflective coatings minimize radiation heat transfer.

3. What materials can be stored in a cryogenic storage dewar?

A cryogenic storage dewar can be used to store a wide range of materials, including biological samples, chemicals, and gases. It is commonly used in scientific research, medical applications, and industrial processes.

4. What are the potential hazards of using a cryogenic storage dewar?

The main hazards associated with using a cryogenic storage dewar include the risk of frostbite from direct contact with the extremely cold materials, as well as the potential for explosion or asphyxiation if the contents are not handled properly. It is important to follow all safety protocols and guidelines when working with cryogenic materials.

5. How are EM waves used in cryogenic storage dewars?

Electromagnetic (EM) waves are used in cryogenic storage dewars to monitor the temperature and level of the stored materials. This is typically done using sensors that detect changes in the EM waves as the temperature or level of the materials changes. EM waves are also used in the construction of the dewar itself, as the reflective coatings on the inner walls help to minimize heat transfer.

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