Cryocoolers are becoming increasingly relevant in the field of military technology, aerospace, medical and many more. Essentially, they are devices that are designed to provide cooling effects at extremely low temperatures. For decades, scientists have been developing these coolers, and they remain a vital part of many applications used by military personnel and beyond. As technology advances, the demand for cryocoolers has increased and continues to grow. This blog post aims to explore cryocoolers and how they're unlocking cryogenic cooling technologies for the military and beyond.

What is a Cryocooler?

A cryocooler is a type of refrigerator designed to reach cryogenic temperatures, typically below 120 K (-153 °C, -243.4 °F). The term is most often used for smaller systems, usually table-top size, with input powers less than about 20 kW.

In most cases, cryocoolers use a cryogenic fluid as the working substance and employ moving parts to cycle the fluid around a thermodynamic cycle. The fluid is typically compressed at room temperature, precooled in a heat exchanger, and then expanded at some low temperature. The returning low-pressure fluid passes through the heat exchanger to precool the high-pressure fluid before entering the compressor intake. The cycle is then repeated 12 times.

Heat exchangers are important components of all cryocoolers. They are used to cool the warm fluid due to heat exchange with the cold fluid. Depending on the kind of heat exchange between the fluids, heat exchangers can either be regenerative or recuperative.

Cryocoolers are used in a variety of applications, including medical equipment, aerospace, and research laboratories.

How Cryocoolers Work:

Cryocoolers operate on an ideal refrigeration cycle, which is essentially a reversible thermodynamic cycle like any other mechanical refrigeration cycle. It involves compressing gas to create heat energy, which is then transferred to a cooling medium, thus producing refrigeration. An internal mechanism is used to remove heat from the cold temperature source, and it is dissipated to the surrounding air.

Most cryocoolers operate by utilizing cryogenic fluids, which are circulated through a series of moving components to create a thermodynamic cycle. Concurrently, there are two fundamental methods by which cryocoolers function:

Regenerative systems employ flow and pressure in an oscillating manner to achieve the desired refrigeration. Typically, these systems utilize pressure oscillators rather than displacers.

Recuperative systems operate by circulating fluids through a predetermined high and low-pressure loop. To achieve cryogenic temperatures, the liquid is compressed at room temperature, subsequently cooled by a heat exchanger, and then expanded at a lower temperature based on the specific requirements of the system. Such cryocoolers necessitate reciprocating pistons or unidirectional compressors without valves. Maintenance also involves the use of oil-removal tools to prevent freezing of oil residues. Other components include orifices, capillaries, and valves or expansion engines, which facilitate appropriate low-temperature expansion.

Types of Cryocoolers:

Cryocoolers come in many different types, each with a different method of cooling. These include Gifford–McMahon cryocoolers, pulse tube cryocoolers, Stirling cryocoolers, Brayton cryocoolers, and others. Gifford–McMahon (GM) cryocoolers were initially developed in 1960. Their application in the 1980s for cooling charcoal adsorbers to approximately 15 K in cryopumps, proved highly valuable in the semiconductor fabrication industry. This enabled the production of extremely clean vacuums, creating a substantial market for these cryocoolers. As a result, significant enhancements were made to their reliability and cost-effectiveness. Gifford-McMahon cryocoolers are often used in industrial applications, such as cooling MRI machines, while Stirling cryocoolers are often used in space applications. Stirling cryocoolers were initially developed in the early 1950s to liquefy air in small quantities, particularly in remote areas. In the 1960s, smaller Stirling cryocoolers found utility in cooling infrared detectors for military night vision equipment.

In a Brayton cryocooler, the inclusion of an expander at the cold end offers the advantage of extracting work and providing gross refrigeration equivalent to the extracted work. This cooling effect holds true even in the case of an ideal gas. However, the presence of a moving component at the cold end may give rise to reliability challenges.

Pulse tube cryocoolers work by taking advantage of the thermal behavior of a gas that is periodically compressed and expanded. The gas heats up when compressed and cools when expanded, and pulse tube cryocoolers utilize this principle to create low temperatures. In a simple pulse tube cryocooler, the compressed gas is pushed through the pulse tube, which causes it to expand, cool, and absorb heat from its surroundings. The expanded gas is then pushed back into the pulse tube where it is compressed again, reheated, and eventually expelled to the outside of the cryocooler. This process is repeated continuously to create and maintain low temperatures. Pulse tube cryocoolers are very popular in the scientific community due to their low noise and lack of moving parts.

Some of the most common types:

• Heat exchangers and regenerators: These are important components of all cryocoolers. A heat exchanger is a device in which the warm fluid gets cooled due to heat exchange with the cold fluid.
• Stirling Refrigerators: These are a type of cryocooler that operates on the Stirling cycle.
• Gifford-McMahon Refrigerators: These refrigerators operate on the Gifford-McMahon cycle.
• Pulse Tube Refrigerators: These use the sudden expansion and release of refrigerant gaseous substances to achieve cooling.
• Joule-Thomson Refrigerators: These refrigerators operate on the Joule-Thomson effect, which involves the cooling of a gas as it expands.
• Helium Cryocooler: This type of cryocooler uses helium as the working fluid.
• Polycold Cryocooler:A Polycold Cryocooler is a type of cryogenic refrigeration system that provides significant cooling power, uses safe, non-flammable, non-toxic, HCFC-Free refrigerants, and is used to capture water vapor and other condensable substances within a vacuum process, as well as in direct cooling applications such as cooling electrostatic chucks used in semiconductor production or cooling various sensor technologies.
• Brayton Cryocoolers: These operate on the Brayton cycle, which is a thermodynamic cycle that describes the workings of a constant-pressure heat engine.
• Regenerative Cryocoolers: These use a regenerative heat exchanger where heat is periodically stored and released by the material.
• Recuperative Cryocoolers: In a recuperative cryocooler, the flow direction of two fluids is constant and simultaneous. The two fluids are separated by a solid boundary across which the warm and cold fluids exchange heat.

Applications of Cryocoolers:

Cryocoolers are used in the military for various purposes. One such use is cooling components of onboard sensors in electronic surveillance planes. The cooling is essential for sensing targets at long ranges that need to be maintained at low temperature levels. They're also essential in removing heat generated during the launch of missiles and keeping infrared sensors at low temperatures in missile defense systems. Thanks to advances in cryocooling, an increase in the effectiveness of missile defense systems has been seen, giving military personnel higher levels of safety and security.

Recent advancements in space cryocooler technology have successfully enabled the utilization of active refrigeration in space missions. Notable demonstrations such as the Sandia National Laboratory Cobra Brass and Multispectral Thermal Imager missions, as well as the National Aeronautics and Space Administration SABER, Hyperion, and AIRS missions, have effectively incorporated active refrigeration to accomplish their mission objectives.

Cryocoolers are also utilized in the medical field for MRI machines. These medical devices need to be kept at freezing temperatures in order to have the ability to conduct medical scans accurately. Additionally, they're also useful in cooling high-temperature superconducting magnets, which are essential in high-energy physics research.

Another application of cryocoolers is in the aerospace industry. They are used in satellites, spacecraft, and other aeronautical applications that require long-lasting cooling effects. They are useful in keeping electronics and cameras at low temperatures. This allows us to conduct space experiments and gather data without being hindered by the extreme temperatures.

Furthermore, cryocooler technology has revolutionized the use of cryogenic storage. They're essential in storing hydrocarbons, which makes it easier to transport natural gas through pipes. They're also used in cooling infrared cameras, which is essential for border surveillance.

Top Five Companies in the Cryocoolers Market:

1.Advanced Research Systems Inc. (ARS):

ARS is one of the top manufacturers of cryogenic equipment and systems globally and has been providing research-grade cryogenic solutions for over 30 years. The company focuses on the development and production of cryogenic equipment, including cryostats, magnets, and dewars. Moreover, they offer a broad range of cryocoolers, including pulse tubes, GM (Gifford-McMahon) coolers, and Stirling cycle cryocoolers. ARS has built a reputation for delivering custom-designed, high-quality equipment, and warranty-backed products to clients across various industries.

2. Air Liquide S.A.

Air Liquide Group is a French industrial gas manufacturer that has been in operation since 1902. The company covers a vast list of industrial, medical, and scientific gas services across the world. They have developed different types of cryocoolers, including pulse tubes, GM coolers, G-M cryocoolers, and PT cryocoolers, and have an extensive customer base in various sectors, including space, research labs, and the medical sector. Air Liquide’s technology has been employed in various applications, including Magnetic Resonance Imaging (MRI), electron microscopy, and cyclotron cooling.

3. AMETEK Inc.

AMETEK is an American company that designs, manufactures, and sells a wide range of electronic equipment and electromechanical gadgets. The company’s HERM (Helium Expansion Reverse-cycle Mode) cryocooler technology is renowned for its flexibility, reliability, and high-performance cooling capabilities in cryogenic applications. AMETEK’s cryocoolers are designed to offer a mass market solution, catering to the various requirements of customers in several industries, including medical, aerospace, defense, and commercial.

4. Brooks Automation Inc.

Brooks Automation is headquartered in the US, founded in 1978, and has operations in numerous countries worldwide. The company provides unparalleled automation and cryogenic solutions to various industries, including the life sciences, semiconductor, and analytical instruments. Their cryocoolers range from traditional Gifford-McMahon (GM) cryocoolers to low vibration coolers, pulse tubes, and more. Brooks' extensive experience, innovative technology, and Vortex cryocoolers make it one of the best cryocooler solution providers in the market today.

5. Chart Industries Inc.

Chart Industries is a global manufacturer and supplier of various cryogenic equipment and services, including storage, transportation, and gas separation systems. The company provides cryocooling solutions for various industries, including life sciences, energy, food processing, and electronics. Chart Industries’ cryocoolers are based on a range of technologies, such as GM, pulse tubes, Joule-Thompson, and Stirling cryocoolers. They also offer cryocoolers for laboratory research, medical, and industrial applications.

These companies are at the forefront of developing cutting-edge cryocooling technology to cater to a wide range of industries, and their innovative solutions have made them the most reliable and reputed cryocooler companies globally.

Conclusion:

Cryocoolers have been around for many years and remain an important technology in many industries. In the military, they are used to enhance missile defense systems and ensure national security. In the medical industry, cryocoolers are used to keep MRI scanners at low temperatures, boosting medical diagnostic accuracy. Furthermore, they're used in the aerospace industry to ensure that spacecraft and satellites remain cool, helping gather important data. The advances in cryocooling technology have improved the cooling times and overall efficiency of the cooling devices, and it's bound to become even more useful in the future. Given the sheer number of applications that cryocoolers have and how essential they are in many industries, it's only a matter of time before they become mainstream. Cryocoolers are and will always remain an essential part of the technological revolution and are unlocking cryogenic cooling technologies for military and beyond.