📘 Comprehensive Lecture Notes on Liquid Nitrogen

👉 Liquid Nitrogen: History, Applications, Storage, and Safety Explained

1. Definition of Liquid Nitrogen

Liquid nitrogen is the liquid form of nitrogen gas, produced when nitrogen gas is cooled to very low temperatures.
It is colorless, odorless, tasteless, and non-flammable.
The boiling point of liquid nitrogen is minus 196 degrees Celsius.
Because of this very low temperature, it is called a cryogenic liquid.

2. Historical Background

Nitrogen gas was discovered in 1772 by Daniel Rutherford, who called it “noxious air” because it did not support life.
In the late 1800s, scientists were trying to liquefy gases such as oxygen and nitrogen.
In 1895, two scientists, Carl von Linde in Germany and William Hampson in the United Kingdom, separately developed machines that could liquefy air by cooling and compressing it.
This was the first time nitrogen was produced in liquid form.
At first, liquid nitrogen was only used in laboratories for experiments.
After World War II, industries began using it widely in medicine, engineering, and food preservation.
Today, liquid nitrogen is produced commercially by fractional distillation of liquid air and supplied by large gas companies all over the world.

3. Important Applications of Liquid Nitrogen

A) Medical Applications

Used in cryotherapy to remove skin problems such as warts and tumors.
Used for cryopreservation of blood, sperm, eggs, and embryos.
Used to store tissues and genetic materials for medical research.

B) Food Industry

Used to freeze food instantly so that flavor and nutrients are preserved.
Used in restaurants and kitchens for special desserts and ice creams with smooth textures.

C) Industrial Uses

Used for shrink fitting of metal machinery parts. Metal contracts when cooled with liquid nitrogen, making assembly easy.
Used to control the temperature of concrete in large constructions to prevent cracks.
Used for temporary shrinking of large components in engineering.

D) Research and Space Science

Used in astronomy to cool cameras that take pictures of stars and galaxies.
Used in physics laboratories to cool superconductors so that they can carry electricity without resistance.
Used in chemical laboratories in vacuum systems and to remove solvents.
Used in aerospace engineering to simulate the very cold temperatures of outer space.

E) Defense

Used to cool infrared sensors in missiles so that they can detect heat more sensitively.

4. Handling of Liquid Nitrogen

Always use protective gloves, safety goggles, and a lab coat when working with liquid nitrogen.
Never allow liquid nitrogen to touch the skin, as it can cause instant frostbite.
Always use liquid nitrogen in a well-ventilated place because it can replace oxygen in the air and cause suffocation.
Use only approved containers for liquid nitrogen. Never keep it in sealed bottles or jars because pressure can build up and cause an explosion.

5. Storage and Carrying Tanks for Liquid Nitrogen

Liquid nitrogen requires special containers because of its very low temperature. These containers are double-walled and insulated to prevent heat from entering. They are also designed to allow some gas to escape safely so that pressure does not build up.

A) Dewar Flask (Small Scale, Laboratory Use)

A Dewar flask is like a very strong thermos bottle.
It is made of stainless steel or sometimes glass.
The walls are double-walled with a vacuum space between them for insulation.
Dewars are open at the top or have a loose cap, never tightly closed, to allow nitrogen gas to escape.
They are used in laboratories for short-term storage and experiments.
Capacity: from a few liters to about 50 liters.

B) Cryogenic Cylinders (Medium Scale, Industrial and Medical Use)

Cryogenic cylinders are tall, stainless steel containers with wheels for movement.
They have double walls with vacuum insulation to keep liquid nitrogen cold.
They are fitted with pressure relief valves to release extra gas safely.
They are fitted with gauges and transfer tubes so that liquid nitrogen can be removed without opening the container completely.
They can store liquid nitrogen for several weeks.
Capacity: about 80 liters to 500 liters.
Used in hospitals, research labs, and industries where a moderate supply is required.

C) Bulk Storage Tanks (Large Scale, Fixed Position)

Bulk tanks are very large, stationary tanks used in factories, hospitals, and research centers.
They are made of carbon steel or stainless steel.
The tanks are cylindrical and vertical, standing on strong foundations.
They have inner and outer walls with vacuum insulation between them.
They are fitted with safety valves, pressure gauges, and pipelines for automatic transfer.
Capacity: thousands of liters.
Used where continuous and large amounts of liquid nitrogen are required.

D) Transport Tankers (For Commercial Transport)

These are huge horizontal tanks mounted on trucks or trailers.
They are made of double-walled stainless steel with a vacuum between the walls.
They have strong insulation and pressure control systems.
They are fitted with valves, transfer hoses, and safety systems to deliver liquid nitrogen safely.
They carry liquid nitrogen from the gas company to industries, hospitals, or storage tanks.
Capacity: several thousand liters.

6. Safety Measures for Storage and Transport

Always keep tanks upright and secured to avoid spills.
Tanks must have pressure relief valves to prevent explosions.
Tanks must be inspected regularly for leaks or damage.
Trained personnel should handle filling and transferring liquid nitrogen.
Avoid storing in closed rooms without ventilation.

7. Summary of Lecture

Liquid nitrogen has grown from a scientific discovery in 1895 into one of the most widely used cryogenic liquids in the modern world.
Its applications in medicine, food, industry, research, defense, and construction show how versatile it is.
Safe storage and transport require special tanks like Dewar flasks, cryogenic cylinders, bulk storage tanks, and transport tankers.
With its amazing usefulness comes the need for strict safety precautions to prevent accidents.
Liquid nitrogen is truly a marvel of science and technology when handled with care and respect.