Lifting gas

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Because of the Archimedes principle, it takes lifting gas for aerostats to create buoyancy. Its density is lower than air (about 1.29 kg/m ³ , 1.29 g/L). It is only slightly lighter than a suitable air gas as a lifting gas.

Video Lifting gas

In theory suitable for lifting

Hot air

Hot atmospheric air is often used in recreational balloons. Under Ideal gas law, a number of gases (as well as gas mixtures such as air) expand when heated. As a result, certain gas volumes have a lower weight due to higher temperatures. The average temperature of air in a hot air balloon is about 212Ã, Â ° F (100Ã, Â ° C).

Hydrogen

Hydrogen, being the lightest gas (7% air density), seems to be the most appropriate gas to lift. But hydrogen has several disadvantages:

• Hydrogen is highly flammable. Some countries have banned the use of hydrogen as a lifting gas for commercial vehicles but allowed for the inflation of free recreation in the US, UK and Germany. The Hindenburg disaster is often cited as an example of hydrogen-borne hydrogen risk. The high cost of helium (compared to hydrogen) has prompted researchers to re-examine the safety issues using hydrogen as a lifting gas: with good engineering and good handling practices, the risk can be significantly reduced.
• Since the hydrogen molecule is so small, it can easily spread through many materials, so the balloon will deflate rapidly. This is one of the reasons why many balloons containing hydrogen or helium are made from Mylar/BoPET.
Helium

Helium is the second lightest gas. Therefore, this is an attractive gas to lift as well. The small size of the helium molecule increases its lift value.

The main advantage is this gas can not burn. But the use of helium has some disadvantages as well:

• The same diffusion problem as described above with hydrogen;
• Helium is expensive.
• Though abundant in the universe, helium is very rare on Earth. The only commercially viable reserves are some natural gas wells, especially in the US, which trap them from the slow alpha decay of radioactive material on Earth. According to human standards, helium is a non-renewable resource that can not be produced practically from other materials. When released into the atmosphere, for example, when a balloon containing helium leaks or cracks, helium eventually escapes into space and disappears.

Steam/moisture

The gas water conditions are lighter than air, not burning and much cheaper than helium. The concept of using steam to lift because it is already 200 years old. The biggest challenge is to create a material that can hold it. In 2003, a university team in Berlin, Germany, had succeeded in making the steam balloon lifted by 150 Â ° C. However, such designs are generally not practical because of high boiling and condensing points.

Ammonia

Ammonia is sometimes used to fill weather balloons. Because of its high boiling point (compared to helium and hydrogen), ammonia is potentially cooled and liquefied in the aircraft to reduce lift and add ballasts (and return to gas to increase lift and reduce ballast). The ammonia gas is relatively heavy, toxic, and irritating.

Metana

Methane, a major component of natural gas, is sometimes used as a lifting gas when hydrogen and helium are not available. It has the advantage of not leaking through the balloon walls as fast as the smaller hydrogen and helium molecules. However, methane is highly flammable and like hydrogen is not suitable for use in passenger carrier airships. It's also relatively dense and a powerful greenhouse gas.

Coal gas

In the past, coal gas, a mixture of hydrogen, carbon monoxide and other gases, was also used in balloons. It's widely available and inexpensive; the lower side is higher density (reduced lifting) and high toxicity of carbon monoxide.

Neon

Neon is lighter than air and can lift balloon. Like helium, it does not burn. However, it is very rare on Earth and expensive, and is among the heavier lifting gases.

Nitrogen

Pure nitrogen has an inert and abundant advantage available, as it is a major component of air. However, since nitrogen is only 3% lighter than air, this is not a clear option for lifting gas.

Vacuum

Theoretically, an aerostatic vehicle can be made using a partial vacuum or vacuum. In early 1670, more than a century before the first manned flight of balloons, the Italian monk Francesco Lana de Terzi envisioned a ship with four vacuum balls.

In a situation that is theoretically perfect with a weightless ball, the 'vacuum balloon' will have a 7% more net lifting force than a balloon containing hydrogen, and 16% more net lifting force than those filled with helium. However, since the balloon walls must remain stiff without exploding, the balloon is not practical to be made with all known ingredients. However, sometimes there is discussion about the topic.

Plasma

Another medium which in theory can be used is plasma: The interlocking ions can put pressure between vacuum and hydrogen and therefore neutralize atmospheric pressure. Energy and containment requirements are not very practical, so it may be of interest to science fiction.

Combination

It is also possible to combine some of the above solutions. A famous example is the RoziÃÆ'¨re balloon that combines a helium core with the outer shell of hot air.


Maps Lifting gas





Hydrogen versus helium

Hydrogen and helium are the most commonly used lifting gases. Although helium is twice as heavy as hydrogen (diatomic), helium is much lighter than air, making this distinction negligible.

The lift in the air of hydrogen and helium can be calculated using the floating theory as follows:

Density at sea level and 0 ° C for air and each gas is:

• Air (? _air ) = 1,292 kg/m ³ = 0,0807 lb/ft ³ .
• Hydrogen (? _{H 2} ) = 0,090 kg/m ³
• Helium (? _He ) = 0,178 kg/m ³

So helium is almost twice as denser than hydrogen. However, buoyancy depends on the difference of the density (? _gas ) - (? _air ) than on their ratio. So the difference in buoyancies is about 8%, as seen from the buoyancy equation:

• F _B = (? _air -? _gas ) * g * V

Where F _B = Floating force (in Newton); g = acceleration of gravity = 9.8066 m/sÃ,² = 9.8066 N/kg; V = volume (in mÃ,³).

Therefore, the amount of mass that can be lifted by hydrogen in air at sea level, equal to the difference in density between hydrogen and air, is:

• (1,292 - 0,090) kg/m ³ = 1,202 kg/m ³

and the buoyancy force for one m 3 of hydrogen in air at sea level is:

• 1 m ³ * 1,202 kg/m ³ * 9.8 N/kg = 11.8 Ã, N

Therefore, the amount of mass that can be lifted by helium in air at sea level is:

• (1,292 - 0,178) kg/m ³ = 1,114 kg/m ³

and the buoyancy force for one m 3 helium in the air at sea level is:

• 1 m ³ * 1,114 kg/m ³ * 9.8 N/kg = 10.9Ã, N

Thus hydrogen supplementary force compared to helium is:

• 11.8/10.9? 1.08, or about 8.0%

This calculation is at sea level at 0 Ã, Â ° C. For higher altitudes, or higher temperatures, the amount of lift will decrease proportionally to air density, but the ratio of hydrogen-lifting capability to helium will remain the same. This calculation does not include the mass of envelopes need to withstand lifting gas.



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High-altitude Balloons

At higher altitudes, the air pressure is lower and therefore the pressure inside the balloon is also lower. This means that although the lifting gas mass and the air mass transferred for the given lift are the same as at lower altitudes, the balloon volume is much greater at higher altitudes.

Balloons designed to be lifted to extreme heights (stratosphere), must be large enough to replace the amount of air needed. That's why the balloons look almost empty at launch, as can be seen in the photo.

A different approach to high-altitude balloons, especially used for long-term flights is superpressure balloons. Superpressure balloons maintain higher pressure inside the balloon than external (ambient) pressure.



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Blown bubble

Due to the enormous density difference between water and gas (water is about 1,000 times denser than most gases), the underwater gas lifting force is very strong. The type of gas used is largely unimportant because the relative difference between the gases is negligible in relation to the water density. However, some gases can melt under high pressure, causing a sudden loss of buoyancy.

Increased submerged balloons will expand or even explode due to strong pressure reductions, unless the gas is able to escape continuously during ascent or balloon is strong enough to withstand pressure changes.



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Balloons on other celestial bodies

Balloons can only have buoyancy if there is a medium that has a higher average density than the balloon itself.

• The bubble can not work on the Moon because it has almost no atmosphere.
• Mars has a very thin atmosphere - the pressure is only 1/160th of the Earth's atmospheric pressure - so large balloons will be needed even for small lifting effects. Overcoming the weight of balloons like that would be difficult, but some proposals to explore Mars with balloons have been made.
• Venus has a CO ₂ atmosphere on the surface. Because CO ₂ is about 50% denser than the Earth's air, ordinary Earth air can be a lifting gas on Venus. This led to proposals for human habitats that would float in Venus's atmosphere at altitudes where pressures and temperatures are the same as on earth. In 1985, the Soviet Vega program sent two balloons to float in the Venus atmosphere at an altitude of 54 km.
• Titan, Saturn's largest moon, has the most solid atmosphere of nitrogen suitable for balloons. Aerobots use is proposed on Titan. Also Titan Saturn System Mission includes balloons to surround Titan.



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See also

• Buoyancy Compensation (flight)
• Cloud Nine (tensegrity scope)
• Lighter than air



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References

Source of the article : Wikipedia