Everything You Need to Know About Cryocoolers
- September 3, 2020
- Controlled Thermal Processing
- Cryogenic Processing
Cryocoolers are refrigerators that can reach extremely low temperatures for use in the field of cryogenics. Although there’s no exact temperature at which a device or process is considered to be cryogenic, the U.S. National Institute of Standards and Technology treats temperatures below −180° C (which is −292° F, or 93 Kelvin) as cryogenic.
Cryogenic refrigerators are used in a variety of industries, and range from small devices that can fit on a table-top, to massive systems used in particular accelerators. The term cryocooler refers to the smaller devices, which have inputs of 2-3 W up to 20 kW.
There are several different types of cryocoolers, all of which rely on a thermodynamic cycle, but have varying arrangements of cryogenic fluids and moving parts.
Let’s take a look at the physics behind cryocoolers, a few different types of cryocoolers you can buy, and some of the industries that they’re used in.
How does a pulse tube cryocooler work?
One of the most widely-used cryocoolers is the pulse tube cryocooler. It was developed in the 1980s and has many industrial uses, from manufacturing to the military. Its main purpose is to cool objects quickly using extremely low temperatures.
Unlike other types of cryocoolers, there are no moving parts in the cold chamber of the pulse tube refrigerator, so it can be used in a wider range of settings. There are several key elements to the pulse tube cryocooler, including a compressor unit with a piston, a heat exchanger, and a regenerator.
The cryocooler is usually filled with helium at 10 to 30 bars of pressure. In spite of its name, there aren’t actually any “pulses” used in the pulse tube cryocooler. A piston in the compressor unit, which is kept at ambient temperature, moves back and forth.
This movement increases or decreases the pressure on the gas, and puts it in contact with the regenerator, usually made of stainless steel or copper wire mesh.
There are several heat exchangers, one of which allows heat to flow out of the device into the surrounding area, and another that transfers cooling power into the area where the object in question will be cooled.
This is similar to the process used in other cryocoolers, but the pulse tube cryocooler is less complicated, making it more affordable and reliable.
Commercial cryocoolers can reach temperatures as low as 4.2 Kelvin, but even lower temperatures have been reached when the helium gas is replaced with an isotope.
Additionally, multi-stage units can be used to reach temperatures lower than that which a single cryocooler can reach on its own.
How much does a cryocooler cost?
The cost of a cryocooling system depends on how specialized you need it to be. Since the equipment is often used in very specialized settings, such as science and medicine, the cost will go up if you need to buy a highly customized cryocooler.
At the same time, as cryocoolers become more widely used in a variety of applications, the cost of more generic cryocoolers is likely to go down. For example, in 2001, the M87 cryocooler was expected to sell for $2,000 per unit in batches of 10,000.
Markets and Markets predicts that cryocoolers will become a $3 billion industry by 2022, which may result in lower costs overall. You can find used cryocoolers sold on Ebay for under $1000, but the quality and reliability of these devices will vary.
Another thing to keep in mind is the cost of helium gas. While traditional cryocoolers use liquid helium, 4K closed cycle cryocoolers do not. Since helium is a scarce resource that may be depleted by 2030, its cost is likely to go up, so investing in a 4K cryocooler that doesn’t require helium may save you money in the long run.
What industries is cryocooling good for?
While many people hear the term “cryogenics” and think of sci-fi stories about freezing human tissue, cryocooling is used in a much wider range of applications.
One of the primary uses of cryocooling is to cool devices that heat up very quickly, such as infrared sensors used in the military or the magnets used in MRI machines.
Pulse tube cryocoolers are also common in astronomical research, and can be found on the earth and in the sky – such as in the Atacama Cosmology Space Telescope and the James Webb Space Telescope.
Additionally, cryocoolers have a range of industrial uses, such as in the manufacturing of semiconductors, where they’ve been used since the 1980s. Some other industries that are expected to contribute to growth in the cryocooler market in the coming years are the fields of cryosurgery and proton therapy, and microsatellite development.
In short, there’s no single industry that cryocooling is good for, and it has a wide variety of uses in medical, military, commercial, and industrial applications.
Cryogenic “hardening” and cryocooling
(Note: The term “hardening” is used here only because the terms wear resistance and hardness are commonly used interchangeably. In fact, wear resistance is dependent on factors beyond hardness and cryogenic treatment addresses those factors. Cryogenic treatment of a previously correctly heat treated component results in an insignificant change in harness; the change may be either an increase or decrease in hardness.
Most of the industrial uses that we’ve looked at involve cooling down a device – such as an infrared sensor – that heats up very rapidly. But another common use of cryocooling is in a process called cryogenic treatment, in which a metal, such as steel, is cooled to a low temperature to improve its mechanical properties.
How does this work? Essentially, the metal is brought down to a temperature of −185 °C (−301 °F), which alters the crystal structure. Cryogenic treatment is most often used on tools made out of high alloy tool steels to enhance wear resistance and fatigue life and hence to extend tool life.
There are also an increasing variety of applications to improve the wear resistance, service life, and dimensional stability of machine parts, automotive components, and precision defence related components.
According to The Fabricator, thermal processing has been around for a long time, and involves varying the temperature of a material in a predetermined, controlled manner to obtain desired mechanical, electrical, magnetic or optical properties.
Conventional heat treatment relies on rapidly cooling of a heated metal in water, air, or oil – a process called quenching. Cryogenic treatment is generally performed after quenching and entails a controlled cooling from room temperature to cryogenic temperatures, generally -300 deg. F or lower, followed by a controlled return to room temp, and finally an excursion to +300 deg. F. or higher.
The goal is to produce a dimensionally stable steel part, that has the correct combination of hardness, wear resistance and impact strength. It takes a precise, finely-tuned process to get it right.
Cryogenic treatment can be used on everything from brake rotors to gun barrels to aluminum optical components, as well as, of course, steel and carbide cutting tools.
Can you buy a cryoprocessor?
Cryoprocessors are not considered especially dangerous or restricted devices, so in a way, yes, anyone can buy a cryoprocessor. You can even find them on eBay.
If your business produces tooling or metal parts that must withstand abrasive wear, then it may be worth investing in a cryoprocessor to do the cryogenic “hardening” process yourself. But if you only need to use a cryoprocessor occasionally, you can hire the team at CTP Cryogenics to do it.
Get your metal parts cryocooled
Depending on how experienced you are with cryocoolers and how often you’ll be using them, it may be more affordable to get your metal parts cooled by professionals.
At CTP Cryogenics, we have thirty years of experience performing cryogenic treatment and thermal processing. Our proprietary process can remove stresses and improve the performance of tools made of steel, iron, aluminum, plastic, and more.
Contact us today to find out more about our process and get a custom quote!