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Cryogenic cooling combines heat transfer with low temperature physics to cool systems below about -250 degrees Fahrenheit (or -150 degrees Celsius, or 120 Kelvin), which is far colder than Antarctica, the coldest place on Earth. It’s a complex science, requiring more precision and elaborate engineering the closer to absolute zero you go.
Below, we’ll discuss some basics of cryogenic cooling, a handful of key applications, and how pressure vessels are used in this field.
Commercially available cryogenic cooling systems exist, but there’s a lot of highly specialized applications that require custom solutions, especially in the aerospace field. Some examples include the following, with more details on a few below:
Many telescopes studying the universe are launched into space because the Earth’s atmosphere blocks their sensors from getting the best data. There’s other things that can obscure data, depending on what the detectors are trying to read. Infrared detectors, for instance, have to be as cold as possible. They detect heat, so if the sensors themselves are warm, they won’t be able to see heat elsewhere.
Particle accelerators use superconducting magnets, which have to be cooled well into the cryogenic temperature range in order to function. The Large Hadron Collider, the biggest particle accelerator in the world, uses liquid helium, a cryogen, to cool its magnets to their operating temperature.
Many vaccines need to be kept within a specific temperature range so the components making up the vaccine don’t degrade. In particular, mRNA vaccines like the Pfizer-BioNTech and Moderna COVID-19 vaccines need to be kept between -76 and -112 degrees Fahrenheit (-60 and -80 degrees Celsius), which is cold enough that using cryogenic cooling is a requirement.
A lot of systems use cryogens (very cold, pressurized liquids like liquid nitrogen and helium) to do much of the cooling. You might have seen liquid nitrogen used to make ice cream in a science classroom. It’s associated with heavy white vapor that sinks to the floor – this is actually water vapor condensing from the extreme cold.
So how are cryogens kept colder than the coldest place on Earth? It’s because temperature and pressure are related. When you increase the pressure on nitrogen gas, it squishes the gas molecules closer together, and the gas temperature goes down. Eventually they’ll get so close together they condense into a liquid, which is more efficient to store and transport since it takes up much less space.
Cryogens have to be stored in pressure vessels to make sure they stay condensed. This includes cryogens used for cooling space systems, so the pressure vessels used to hold them need to be able to withstand a rocket launch and the harsh, zero gravity environment of space.
Pressure vessels designed for cryogenic cooling have to be able to withstand some additional requirements, in addition to the required pressure. Here’s a couple examples:
Cryogenic cooling can change a material’s properties, often making the material more brittle. Some of these effects last even after the material is returned to room temperature, so it’s important to understand how the temperature extremes will impact the material and design. The rate of temperature change may need to be controlled as well, to prevent the material from warping or cracking.
Seals need to be carefully designed, especially given how brittle rubber gets at cryogenic temperatures. It tends to shatter. O-rings can be made from malleable metals instead, as clamping two sides of a fitting together over the O-ring will deform the metal to precisely fill the gaps between the fittings. These types of O-rings need to be replaced every time they are unclamped.
Rexarc develops and manufactures custom stainless steel and carbon steel pressure vessels for the aerospace industry, among others. Learn more about our ASME standard pressure vessels here, or reach out to us with any questions you have about pressure vessels!
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