Cryogenics
Liquid nitrogen: characteristics, production, and application
Medical institutions, automobile manufacturers, food factories, and more. Almost every cryogenic industry uses liquid nitrogen at some point because liquid nitrogen is not only affordable but also very versatile.
But what is liquid nitrogen exactly? Why is it so popular, and what are its main applications? Read on for a comprehensive answer to these questions.
What is liquid nitrogen?
Liquid nitrogen is formed when nitrogen is cooled to temperatures far below zero. The colorless liquid has a density of 806.59 kg/m³ at atmospheric pressure and an energy capacity of 199.32 kJ/kg. In its liquid form, it manifests itself very similar to water. Yet, the significant temperature difference produces a white mist from the condensation of water vapor when it’s exposed to ambient air.
The development of liquid nitrogen dates back to the late 19th century when scientists such as Carl von Linde and James Dewar ardently worked to liquefy various gases. Their work laid the foundation for modern-day cryogenics.
Today, liquid nitrogen is used for a tremendous variety of applications. Think of cooling biological materials or foods, performing medical procedures, shrinking automobile parts for so-called shrink fits, and providing cooling during scientific experiments.
Liquid nitrogen temperature
Exactly how cold is liquid nitrogen? The boiling point of liquid nitrogen at normal atmospheric pressure is -196°C. Below this temperature, the substance transforms from gaseous to liquid. When the temperature rises above this point, the liquid form is lost, and nitrogen will return to its gaseous state.
Liquid nitrogen production
The production of liquid nitrogen takes place in air separation plants and typically includes the following steps:
- Purification: In the first stage, the air is filtered to remove CO2, dust, and water that may interfere with the liquefaction process.
- Compression and cooling: Next, the air is compressed and cooled according to a multi-stage gas compression and expansion principle. Heat is extracted during the compression stages, while the gas cools during expansion. This principle is similar to a refrigerator but much more efficient and powerful.
- Condensation: Even further cooling reaches temperatures where argon (Ar) and oxygen (O2) condense and liquefy and are separated from the air stream. Lowering the temperature even further to -196 °C turns nitrogen into a liquid.
The only gases not filtered out of the air are hydrogen (H2) and helium (He). These remain in gas form since the gas is still too hot to become liquid at that point.
Liquid nitrogen storage
After liquid nitrogen is produced, the cryogenic liquid must be stored safely. This can be done in several ways:
- In large tanks for long-term storage.
- In containers or dewars for storage of smaller quantities or transport.
When storing liquid nitrogen, it is crucial to avoid warming up the tank, dewar, or transfer line as much as possible; a temperature increase will cause the cryogenic liquid to release gas. Gas formation causes the pressure in the system to increase and – if the gas can evaporate from the system – causes a loss in supply. When the gas cannot leave the system, the pressure increases significantly, leading to a dangerous situation.
Vacuum insulation
The ultimate solution for storing and transporting liquid nitrogen safely and at the right temperature is vacuum insulation. This technique creates a vacuum between the double walls of storage vessels or transfer lines. Heat transfer is almost completely blocked when a vacuum is combined with a multilayer combination of aluminum foil and glass paper.
Would you like to know more about this technology? Then continue reading on our page about vacuum technology.
Liquid nitrogen uses
Due to its extremely low temperature and inertia, liquid nitrogen is a versatile gas that is used in many different industries. Here are five well-known examples of the application of liquid nitrogen:
- Liquid nitrogen freezer for food: These cryogenic freezers (for example, tunnel freezers or spiral freezers) use liquid nitrogen to cool and freeze food rapidly.
- Cooling tray: In food production and industrial processes, a cooling tray filled with liquid nitrogen is used to rapidly cool materials or equipment by immersing the product in nitrogen.
- Filling station: Filling stations are crucial in both medical and research laboratories to readily and controllably draw small amounts of liquid nitrogen from large storage tanks.
- Cryosauna: In the wellness and sports industry, cryosaunas with liquid nitrogen vapor are used for cryotherapy.
- Test chamber: Liquid nitrogen test chambers are used in technology and material sciences to test the performance and durability of materials and devices at extremely low temperatures.
The above five cryogenic applications are just a small sample of all the possibilities liquid nitrogen offers. Does an application require extreme cold? Then, chances are that liquid nitrogen offers the required potential.
Hazards and safety
Like any extremely cold substance, liquid nitrogen comes with some hazards and risks:
- Expansion upon evaporation: Liquid nitrogen expands significantly upon evaporation, which can lead to pressure build-up and explosion hazards in enclosed spaces.
- Choking hazard: Nitrogen gas is odorless and can displace oxygen, posing a choking hazard in poorly ventilated spaces.
- Cold burns: Direct contact with liquid nitrogen can cause severe burns.
Generating liquid oxygen: Due to the extremely cold surface of poorly insulated pipe sections, liquid oxygen can spontaneously form. This can create an increased risk of fire hazard. - Errors: Errors occur, but mistakes can have severe consequences while handling hazardous materials.
Fortunately, the dangers can be effectively mitigated with the proper safety precautions. Ensure personal protection, adequate ventilation, regular inspection of storage containers, and appropriate training in handling cryogenic liquid.
Demaco’s liquid nitrogen infrastructures
Even more important than training and fresh air is the proper infrastructure. For example, use a gas vent or degasser to remove any gas bubbles and use a vacuum to insulate an infrastructure as much as possible.
Would you like to know more about Demaco’s vacuum-insulated and quality improvement products? Feel free to contact us or take a look at our products and projects for more information.
