Cryogenic Refrigeration
Refrigeration and cryogenics have garnered significant attention in the fields of engineering and science due to their ability to extract heat from low-temperature bodies and transfer it to a body willing to accept it. Refrigeration processes typically operate within a temperature range of 120 to 273 K, while cryogenics involves temperatures below 120 K and the liquefaction of gasses such as methane, oxygen, argon, nitrogen, hydrogen, and helium. In this blog, we have presented a brief history of refrigeration and cryogenics, the equipment and materials required for such cooling units, their storage, and transportation, performance parameters, and applications in various industries.
Refrigeration:
Refrigeration is the process of removing heat from an enclosed space or a substance and rejecting it elsewhere with the primary goal of lowering and then maintaining the temperature of the room or substance. “Cooling” refers to any natural or artificial process that dissipates heat. The field of study that deals with the artificial production of extremely low temperatures are referred to as cryogenics, which we cover after refrigeration.
The history of refrigeration has seen rapid and continuous development, beginning at the turn of the 20th century. Generally, refrigeration involves making materials colder by extracting heat from them. In a commercial setting, refrigeration is often used for food preservation and air conditioning. By keeping food at cooler temperatures, the growth of bacteria and spoilage can be prevented. In the early days of refrigeration, people used ice boxes to keep certain foods cold and fresh. Household refrigerators became more common in the early 1900s, but they were only affordable for the wealthy. Freezers, which became a standard part of refrigerators after World War II, allowed for the widespread popularity of frozen foods.
The equipment needed for refrigeration depends on various factors, including the substances and fluids working in the system. A crucial aspect of refrigeration is the selection of the appropriate refrigerant, which depends on the specific system it will be used in. Hydrocarbon refrigerants commonly used include propane, ethane, propylene, and ethylene. "Non-hydrocarbon liquid refrigerants include nitrogen, oxygen, neon, hydrogen, and helium”.
Working Principle of Refrigerator:
Refrigerators work on the second law of thermodynamics. In the process of refrigeration, unwanted heat is taken from one place and discharged into another. The common refrigerator that we have in our homes works on the principle of evaporation. A refrigerant is a substance used in a heat cycle to transfer heat from one area and remove it from another. A refrigerant, when passed through the food kept in the refrigerator, absorbs heat from these items and transfers the absorbed heat to the surrounding air at a lower temperature.
Applications of refrigeration:
The air conditioning of private homes and public buildings, as well as the refrigeration of foodstuffs in homes, restaurants, and large storage warehouses, are probably the most widely used current applications of refrigeration. The use of refrigerators in our kitchens for the storage of fruits and vegetables has allowed us to include fresh salads in our diets all year long, as well as safely store fish and meats.
Refrigeration has numerous applications in commerce and manufacturing. Refrigeration is used to liquefy gases such as oxygen, nitrogen, propane, and methane. It is used in compressed air purification to condense water vapor from compressed air to reduce its moisture content. Refrigeration is used in oil refineries, chemical plants, and petrochemical plants to keep certain processes at the required low temperatures (for example, in the alkylation of butenes and butane to produce a high-octane gasoline component). Refrigeration is used by metal workers to temper steel and cutlery. Refrigeration is required when transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes, and seagoing vessels.
Dairy products require constant refrigeration, and it was only in the last few decades that it was discovered that eggs needed to be refrigerated during shipment rather than waiting to be refrigerated after arrival at the grocery store. Meat, poultry, and fish must all be stored in temperature-controlled environments before being sold. Refrigeration also keeps fruits and vegetables fresher for longer.
One of the most influential applications of refrigeration was in the development of Japan’s sushi/sashimi industry. Before the discovery of refrigeration, many sushi connoisseurs suffered great morbidity and mortality from diseases such as hepatitis A. However, the dangers of unrefrigerated sashimi were not brought to light for decades due to the lack of research and healthcare distribution across rural Japan. Around the mid-century, the Kyoto-based Zojirushi Corporation made breakthroughs in refrigerator design, making refrigerators more affordable and accessible to restaurant owners and the general public.
Home and consumer use:
Safer refrigerators for home and consumer use became possible with the invention of synthetic refrigeration systems based primarily on a chlorofluorocarbon (CFC) chemical. The DuPont Corporation’s trademark Freon refers to these CFC and later hydrochlorofluorocarbon (HCFC) and hydrofluorocarbon (HFC) refrigerants.
Cryogenics:
Cryogenics is a branch of physics or engineering that investigates the production of extremely low temperatures as well as the behavior of materials at such temperatures. Liquid gases such as liquid nitrogen or liquid helium can be used to achieve extremely low temperatures. These materials are called cryogens.
Some cryogens, such as liquid nitrogen, are used to quickly freeze foods and vaccines, as well as for chemical reactions that require low temperatures. Cryogenic oxygen and hydrogen are useful as rocket fuels for space flight. Metals and other materials have gained strength and resistance to wear thanks to controlled cryogenic treatment.
At cryogenic temperatures, materials such as rubber, plastic, and carbon steel can become so brittle that very little stress can break the material. To avoid problems with cold embrittlement, materials like stainless steel, copper, brass, and most alloys of aluminum should be used in the cryogen containment systems
Cryogenics is the study of material behavior at extremely low temperatures, typically less than -150 °C (-238 °F). It entails the creation and application of extremely low-temperature materials, as well as the investigation of their physical and chemical properties. Cryogenics is used in a wide range of disciplines, including physics, engineering, biology, and medicine. In physics and engineering, cryogenics is used to study the behavior of materials at low temperatures and to design and operate cryogenic equipment, such as refrigerators and cryostats. Cryogenics is a technique used in biology and medicine to preserve biological materials such as blood, tissue, and cells at low temperatures to prevent deterioration. It is also used in the fabrication of superconducting materials as well as in the study of superconductivity.
Cryogenic processing
Cryogenics advanced during World War II, when scientists discovered that metals frozen at low temperatures were more resistant to wear. Ed Busch founded the commercial cryogenic processing industry in 1966 on the basis of the “cryogenic hardening” theory. With a background in the heat treating industry, Busch founded CryoTech in Detroit in 1966. Though CryoTech later merged with 300 Below to form the world’s largest and oldest commercial cryogenics company, they first experimented with the possibility of increasing the life of metal tools by 200 to 400 percent by using cryogenic tempering instead of heat treating.
In the late 1990s, the applications of cryogenics developed into the treatment of other parts, achieving more than just increasing the life of a product. Musical instruments (improved sound quality), baseball bats (larger sweet spot), golf clubs (larger sweet spot), racing engines (improved performance under stress), firearms (less warping after continuous shooting), knives, razor blades, brake rotors, and even pantyhose are examples.
Liquid nitrogen and other cryogens are also used in specialty chilling and freezing applications. Some chemical reactions, such as those used to produce the active ingredients in popular statin drugs, must take place at extremely low temperatures of around -100 °C. To remove reaction heat and maintain a low-temperature environment, cryogenic chemical reactors are used. Furthermore, in “blast freezing” or “immersion freezing” systems, nitrogen is required for the freezing of foods and biotechnology products such as vaccines.
Cryogenic Fuels
Cryogenic fuels are fuels that must be stored at extremely low temperatures in order to remain liquid. These fuels are used in machinery that operates in space (e.g., rockets and satellites), where ordinary fuel cannot be used due to the extremely low temperatures frequently encountered in space, as well as the absence of an environment conducive to combustion (on Earth, oxygen is abundant in the atmosphere, whereas human-explorable space is a vacuum where oxygen is virtually non-existent). Cryogenic fuels are typically liquefied gases such as liquid hydrogen.
Rockets have been powered by cryogenic fuels, primarily oxygen and hydrogen. NASA’s workhorse space shuttle, for example, uses cryogenic oxygen and hydrogen fuels as its primary means of entering orbit. All of Sergei Korolev’s rockets for the Soviet space program did well, causing a schism between him and rival engine designer Valentin Glushko, who believed that cryogenic fuels were impractical for large-scale rockets like the ill-fated N-1 rocket.
How are cryogenic materials stored and transported?
Cryogens should be stored in containers specifically designed to house them. The containers should be insulated and double-walled. Store all cryogenic liquid containers upright in well-ventilated areas. Handle them carefully, and avoid dropping, rolling, or tipping them on their sides.
The vessel used to transport cryogenic liquids must be designed specifically for cryogenic liquid use and be in good operating condition. Household-type thermos bottles and Styrofoam cups are not appropriate cryogenic liquid containers. Filled cryogen dewars larger than 5 liters must be moved on a sturdy wheeled cart.
Parameters required to determine the performance of cryogenic units:
Coefficient of Performance:
The performance and energy-saving ability of a refrigerator are measured in terms of the system’s Coefficient of Performance (C.O.P.). This is defined as the heat removed at a low temperature, i.e., the cooling effect, QC, divided by the work input, Win, into the system:
Thermal Efficiency:
The performance of a steam power plant process can be measured in a manner somewhat analogous to the C.O.P. for a refrigeration system. The thermal efficiency, hth, of a work-producing cycle is defined as the ratio of work produced to heat added. Thus,
Applications:
Many cryogenic applications make use of liquefied gases such as liquid nitrogen and liquid helium. The most commonly used element in cryogenics is liquid nitrogen, which can be legally purchased all over the world. Liquid helium is also commonly used and allows for the lowest temperatures possible.
In larger commercial operations, these gases are stored in special containers such as Dewar flasks, which are about six feet tall (1.8 meters) and three feet (91.5 centimeters) in diameter, or giant tanks. Dewar flasks are named after James Dewar, the first person to liquefy hydrogen. Smaller vacuum flasks enclosed in protective casings are commonly displayed in museums.
Natural gas, which is used as a fuel, is frequently transported by ship in a liquefied form known as LNG (liquefied natural gas). Cryogenic transfer pumps are used at LNG piers to transfer material from LNG carriers to LNG storage tanks.
- In large cities, it is difficult to transmit power by overhead cables, so underground cables are used. But underground cables get heated and the resistance of the wire increases, leading to a waste of power. Superconductors could be used to increase power throughput, although they would require cryogenic liquids such as nitrogen or helium to cool special alloy-containing cables to increase power transmission.
- Cryogenic gases are used in the transportation and storage of large masses of frozen food. When very large quantities of food must be transported to regions like war zones, earthquake-hit regions, etc., they must be stored for a long time, so cryogenic food freezing is used. Cryogenic food freezing is also helpful for large-scale food processing industries.
- Cryogenics technology using liquid nitrogen and CO2 has been built into nightclub effect systems to create a chilling effect and white fog that can be illuminated with colored lights.
- Cryogenic cooling is used to cool the tooltip at the time of machining in the manufacturing process. It increases the tool's life. Oxygen is used to perform several important functions in the steel manufacturing process.
- Many rockets use cryogenic gases as propellants. These include liquid oxygen, liquid hydrogen, and liquid methane.
- By freezing the automobile or truck tire in liquid nitrogen, the rubber is made brittle and can be crushed into small particles. These particles can be used again for other items.
- Experimental research on certain physics phenomena, such as spintronics and magnetotransport properties, requires cryogenic temperatures for the effects to be observed.
Other Applications:
Cryogenics plays a crucial role in the chemical processing industry, particularly in the recovery of valuable feedstocks from natural gas streams, upgrading the heat content of fuel gas, purifying various processes and waste streams, and producing ethylene. Cryogenic air separation also produces gases such as nitrogen, oxygen, and argon, which are used in a range of applications:
- The steel manufacturing industry
- The chemical processing and manufacturing industries
- The electronic industries
- Enhanced oil recovery processes
- Partial oxidation and coal gasification processes
Cryogenic gases like hydrogen and carbon monoxide have numerous applications in the chemical and metal industries, whereas helium is used in welding, medicine, and gas chromatography. Cryogenic liquids like liquid nitrogen are frequently used to freeze food, and cryogenic cooling techniques are used to recover rubber tires and scrap metal from old cars. Cryogenic freezing and storage are also required for biological materials such as blood, bone marrow, skin, tumor cells, tissue cultures, and animal sperm. Cryogenics is also used to cool the highly conductive magnets used in non-invasive body diagnostics in magnetic resonance imaging (MRI).
Conclusion:
Cryogenic refrigeration has several advantages, including the ability to preserve materials for long periods of time without degradation and the ability to store materials at a very stable temperature. It is also highly energy efficient, as cryogenic fluids have a high heat transfer coefficient, which means they can transfer heat quickly and efficiently.
Overall, cryogenic refrigeration is a valuable technology that allows for the preservation and storage of materials at extremely low temperatures, making it useful in a variety of applications.