Liquid Helium

What is elemental helium?

The element Helium with the chemical symbol He, atomic number 2 and weight 4.002602 is in the category of noble or inert gases, which has low reactivity and has little solubility compared to other monoatomic gases. The melting and boiling temperature of this element is very low compared to other elements and is close to absolute zero, and for this reason, it exists mostly in gas form, but it is liquefied under special conditions, in which case it is the only liquid that turns into a solid when the temperature decreases. can't In fact, this substance remains in a liquid state at standard pressure up to absolute zero temperature and turns into a solid only by increasing the pressure. Other important features of this element include high heat conduction and heat capacity, no color, no odor, no taste, completely non-toxic, low impact on nature, lightness, cooling property, and very low electronegativity.




Chemical Symbol: He

Element Name: Helium

Standard Atomic Mass: 4.003gr/mol

Atomic Number: 2

Liquid Density At Boiling Point: 0.145gr/cm3

Density At The Pressure Of One Atmosphere: 0.1786gr/L

Boiling Point: -268.93ċ

Melting Point: -272.20ċ

Critical Point: 0.227mpa, 5.19k

Heat Of Vaporization: 0.0829kj/mol

Heat Capacity: 20.786j/mol. K

Heat Of Fusion: 0.0138kj/mol


Uses of helium gas:

-As a coolant for superconductor magnets (MRI and NMR machines) and nuclear reactors

-Particle physics research

-As a discharge gas to introduce pressure

-As a lifter of balloons and airships (for advertising, atmospheric research, military reconnaissance, etc.)

-As a protective layer or coating in electric arc welding

-As a leak detector in ultra-sensitive instruments

-As a supplement for space rocket fuel

-mixed with oxygen gas, nitrogen gas and sometimes hydrogen as a helper for better oxygenation to divers at high depths, especially in underwater welding

-In combination with some gases for laser cutting

-As a carrier gas in the gas crocatography device

-As a protective gas in the cultivation of silicon and germanium crystals

-Cleaning fuel tanks

-Filling the empty space of the fuel tank

-In devices related to lighting, such as car lights or billboards, which are used due to the property of emitting and absorbing electromagnetic waves.

-Breathing helium gas reduces the number of breaths in a person due to its low density and difficult dissolution in nervous tissues, which is useful in some respiratory patients and has a therapeutic effect.

-Organ protection in medicine

-The mixture of this gas with neon leads to the creation of a low-power laser with a red beam, which is used in devices such as barcode readers and laser pointers.

-The combination of helium gas with hydrogen gas as a combustible gas in tests related to car emissions

-The combination of helium gas with heavier gases such as xenon, which has a high heat capacity, in thermoacoustic coolers.

-Helium gas provides a protective atmosphere in the production of reactive materials such as titanium and zirconium

What is liquid helium?

Liquid helium is used as a refrigerant. As mentioned, the helium element is in a gaseous state at standard temperature and pressure, but if the temperature is cooled to about 4 degrees Kelvin (-270 degrees Celsius or -2.452 degrees Fahrenheit) at standard pressure, this element turns into a liquid state. comes. The boiling and condensation points of helium depend on its isotope type, and the most common type of helium isotope is helium 4, and helium 3 isotope is rare. Isotopes 3 and 4 are the only stable isotopes of helium. The temperature required to produce liquid helium is very low because helium atoms have very little attraction to each other and the intermolecular forces in helium are very weak because helium is a noble gas. Is. Helium is found in the earth's atmosphere in a very small amount due to the erosion of certain minerals, it is also present in some mineral waters. Helium is present in certain natural gases in commercially available quantities. Today, most commercial helium is separated from natural gas during a cryogenic process. Normally less than 1% of natural gas volume is helium. Helium gas is separated and purified and becomes a liquid. Liquid helium is transported from the production site for storage and later consumption. Transfer tankers ranging in size from 5,000 to 11,000 gallons have a space insulated with vacuum or nitrogen shielding gas and multilayer insulation. This design reduces heat transfer and evaporation of helium along the transfer path. Like helium gas, liquid helium is colorless, odorless and neutral. Liquid helium is not flammable or corrosive, so there are no special restrictions for its transportation. The only point for containers holding liquid helium is that they must be resistant to the very low temperature of liquid helium and the connections of the container must withstand its high pressure. Helium is supplied in tanks of different sizes according to the needs of the consumer. The liquid helium capsule has two walls. They empty the air between the two walls and use several layers of insulation. To use helium capsules, it is necessary to consider a special regulator to reduce the pressure. A cryogenic or cryogenic tank with the Dewar brand is a device for storing materials whose boiling point is much lower than room temperature (such as helium) is used. These tanks can store materials at the right temperature and pressure for transportation. These tanks are used to store gases at a maximum working pressure of 18, 22 and 36 bar and a design temperature of 50 to -270 degrees Celsius. Cryogenic tanks are made of two or more layers with a vacuum between these layers. This creates a very good thermal insulation between the inside and outside of the cryogenic tank, which reduces the rate of evaporation of the liquid inside the tank.

-Cryogenic tanks are made of stainless steel and aluminum vertically and horizontally.

-Cryogenic tanks must be upright and restrained and stored and used in a well-ventilated environment.

In what field is liquid helium used the most?

Giant magnets of MRI machines all over the world need liquid helium for cooling, and this machine itself is a vital tool in medical diagnosis, and it can be said that liquid helium indirectly plays a role in saving human lives. The consumption of liquid helium for an MRI machine cannot be accurately determined because according to the number of photographs, the amount of consumption and the need for cooling will increase, but in general, it can be said that one machine consumes up to 6 thousand liters of liquid helium. slow Liquid helium has so far been the most effective and safest coolant for MRI machines.

How is helium gas sold?

Helium in gas form is usually sold in 50-liter capsules with a pressure of 150 to 200 bar. Helium gas is an imported gas with a purity of 999.999% (Grade 5), 999.999% (Grade 6) and 999.995%. % (grade 5.5) is sold. Helium gas has a right round valve due to its inertness. The valve of helium gas cylinders is usually BS3 or DIN6.

Helium in liquid form is usually supplied in tanks known as Doer or Dewar, which are mostly available in volumes of 200, 250 and 400 liters.

Safety information when working with helium:

The temperature of liquid helium is very low and a person may suffer from cold burns.

Inhalation of helium in a large amount can lead to sudden rupture of the lungs and compression of the middle ear due to the intensity of the high flow. Dizziness, drowsiness, freezing, fatigue, nausea, vomiting, loss of consciousness and death are other effects. . This death may result from a mistake in decision, confusion or loss of consciousness.

A very large leak of helium causes the oxygen concentration to decrease and causes death within seconds without warning.


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