How Cryogenic Fluids Work

Cryogenic fluids are used in dozens of industries, usually to freeze objects at extremely low temperatures or to cool down devices that would otherwise get overheated, such as infrared sensors and MRI machines. But not all cryogenic fluids and cryocoolers are the same, so it’s important to understand how they’re used in different contexts.

Although they have a wide range of applications in medicine, manufacturing, and even space exploration, these fluids can be dangerous when not used properly.

In this article, we’re going to look at the science behind cryogenic liquids, what they’re used for in various industries, and how to handle them safely.

What is cryogenic fluid?

A generally accepted definition of a cryogenic liquid is one that has a boiling point under -130 °F (-90 C°). In other words, they’re incredibly cold when they’re in their liquid state, but they only turn into liquids at certain temperatures and pressures.

Cryogenic liquids are gases at room temperature and pressure, and they include some common elements like hydrogen, helium, and nitrogen.

Carbon dioxide and nitrous oxide are considered cryogenic fluids as well, even though their boiling points are a little higher than the common definition.

Cryogenic fluids typically fall into three categories:

  • Inert gases are those that don’t burn or react chemically with other elements, such as neon, argon, krypton, nitrogen, and helium
  • Flammable gases are those that can burn when the liquid is turned into a gas and exposed to the air, such as methane and hydrogen
  • Oxygen is treated as a separate category because it has unique properties that make it more dangerous than other cryogenic fluids. Because it has 4,000 times as much oxygen by volume when stored as a liquid, even materials that aren’t usually combustible, such as steel, can burn when exposed to it.

Liquid helium can reach the lowest temperatures out of all the cryogenic fluids, but liquid nitrogen is used most often, since it’s legal to purchase it anywhere in the world.

What is it used for?

Cryogenic fluids are used in a range of industries, from medicine to astronomy. Some devices, such as MRI machines, infrared cameras, and telescopes heat up very quickly, so cryogenic fluids are used to cool them and keep them at a stable temperature.

Liquid nitrogen is used in the production of some foods and medical products, such as vaccines, in which blast freezes or immersion freezers are used to preserve them.

Cryogenic processing can be used to improve the durability of certain tools, especially those made out of steel. By treating tools at temperatures of -300 °F, this process can make them more resistant to wear and increase their lifespan by 200% to 400%

Some cryogenic fluids are used as fuel, such as liquid hydrogen. These fuels can be used in space, including on rockets and satellites, where other fuels cannot, because they can burn at low temperatures and in the absence of oxygen.

Finally, some cryogenic fluids are simply used for decor. Because they produce a fog that can be lit up with lights, some fluids, such as CO2 and liquid nitrogen, are often used in movies and nightclubs to produce an atmospheric effect.

Is liquid nitrogen cryogenic?

Liquid nitrogen is one of the more commonly used cryogenic fluids because it’s safe and extremely effective when handled properly. Liquid nitrogen is inert and noncorrosive, so it doesn’t carry the same risk of combustion that oxygen does. 

It’s also found at high concentrations in the atmosphere (over 78% by volume), making it relatively cheap to store and transport.

However, because it’s tasteless, odorless, and colorless, it can’t be detected by human senses. This means that if the concentration of nitrogen in the air is too high relative to oxygen, it can result in dizziness, loss of consciousness, and even death. Other risks include severe burns when exposed to the liquid in its cold state.

Liquid nitrogen also has many medical uses, including cryotherapy. This can be either localized cryosurgery, such as when liquid nitrogen is applied to the skin to freeze off warts, moles, and other abnormalities, or whole body cryotherapy.

How are cryogenics used today?

Cryogenics may sound like science fiction, but it’s actually been around for a long time. Scientists began to experiment with liquifying gases in the 1800s, and by the end of the century, Sir James Dewar managed to discover the boiling point of hydrogen.

One of the devices used to store cryogenic fluids is named after him: the Dewar Flask, which is basically a Thermos that uses a vacuum chamber as insulation.

Now, cryogenic liquids can be found in a range of industries, including:

  • Cryobiology: In addition to cryosurgery, cryogenics can be used to preserve organs outside the body, as well as embryos and cell tissues. This means it’s used in vitro fertilization, organ transplants, and other procedures. Other uses, such as cryonics, are more speculative, but continue to be researched.
  • Food preservation. Liquid nitrogen is the most commonly used cryogenic fluid for this purpose, because it can be sprayed on foods, such as fresh produce, to flash freeze them. It evaporates before the produce is eaten, meaning the food can last longer without the need for any harmful chemical preservatives.
  • Cryoelectronics. One of the limitations on computing power is the amount of heat that superconductors generate. By operating computers in extremely low temperatures, electrons can move around more easily.

These are just a few of the most recent applications for cryogenics, but more uses are being discovered each year. From biology to astronomy, cryogenic fluids are becoming an indispensable part of many industries.

Cryogenic fluids used in metal treatment

Cryogenic fluids were first used for treating metals in the mid-1900s, after World War II. Although heat treating techniques, including tempering and quenching, had been used for centuries, cryogenics offered the possibility of faster, more effective treating.

This treatment process used today, which subjects metals to both extremely high and low temperatures, causes certain metals, such as steel, to develop a different crystal structure than they would have if they were allowed to cool at room temperature.

In more precise terms, the metal’s austenite is turned into martensite, which hardens the material and produces more durable, longer-lasting tools.

Cryogenic processing involves more than just dipping your tools into liquid nitrogen, though. This is a finely-tuned process controlled by computers, and tailored to each metal. It takes place in several stages and can last up to 24 hours.

Handling cryogenic fluids safely

If you’ll be handling cryogenic fluids at your workplace, it’s important to understand how to protect yourself from some of their more dangerous properties. As we’ve seen, some fluids are more combustible than others, and all of them are too cold to touch.

Here are a few basic safety precautions to adhere to, regardless of which state (gas or liquid) the cryogenic materials are in:

  • Use Personal Protective Equipment (PPE). You should never handle cryogenic fluids without appropriate gloves and eye protection. Not only are they dangerous to human tissue, they can cause other materials to break as well. Plastic, rubber, and even steel tools can become brittle and shatter without warning.
  • Ensure proper ventilation. When cryogenic liquids turn into gas, they expand rapidly and can easily fill an enclosed space. Nitrogen gas itself isn’t dangerous, but it can reduce the amount of oxygen in the air to dangerous levels. Don’t go into a room if the oxygen levels are below 19.5%.
  • Don’t be fooled by fog clouds. While fog clouds are a sign that cryogenic fluids have been released, they may only represent a small portion of the leaked fluids.  A single liter of liquid nitrogen can expand to 695 liters at room temperature!
  • Treat liquid oxygen carefully. Liquid oxygen is more dangerous than the other cryogenic fluids due to the increased risk of combustion. Even items that aren’t ordinarily flammable can burn if liquid oxygen is spilled on it. Items of clothing that have been exposed to liquid oxygen should be aired out for an hour.

This is just an overview of what to look out for when handling cryogenic fluids. Always seek out professional advice specific to your industry.

How cold do cryogenic fluids run?

Cryogenic fluids are usually measured in Kelvin, which uses 0 as the lowest and coldest possible temperature. Each fluid has a boiling point measured at 1 atm of pressure, but remember, this can vary if more or less pressure is applied.

The boiling points for some common cryogenic fluids are:

  • Neon: 27K
  • Helium: 4K
  • Nitrogen: 77K
  • Hydrogen: 20K
  • Liquid oxygen: 90K

As you can see, Helium is the coldest cryogenic fluid, with a boiling point of –452 °F or –269 °C. Although reaching a temperature of 0K is possible in theory, 4K is the coldest that today’s commercially available cryocoolers can go.

Need treatment for your metal parts?

Treating your metal parts with cryogenic fluids is definitely not something you should do at home. At CTP Cryogenics, we’ve had 40 years of experience to get it right.

Our proprietary processing techniques are available for steel, iron, aluminum, Titanium and many other alloys. No matter what industry you work in, Deep cryogenic processing can reduce wear and tear on your equipment and increase the lifespan of your metal tools.

Contact us today to learn more about our process and get a custom quote!