Carrier gas is a gas which is used as a filling for airships and gas balloons. It has a lower density than the air surrounding the aircraft. This results according to Archimedes' principle, a static buoyancy.
The two main carrier gases are hydrogen and helium.
Gases used for this purpose in question (about 1.293 kg/m3 under normal conditions) have a lower density than air. Ideal in physical terms, is for hydrogen as the lightest of all elements with an atomic mass of only ~ 1.0 u, H2 molecular mass of 2u and a density of only 0.0899 kg/m3. As this gas is also relatively easy and inexpensive to make, it was prevalent as carrier gas until well into the 20th century. However, hydrogen is highly inflammable and in a mixture with oxygen, for example, from the air, even explosive ( oxyhydrogen ). Because of these disadvantages, he was gradually supplanted by the inert noble gas helium, as soon as it could be produced in sufficient quantities. To this end, Before the Second World War, however, exclusively to the U.S. in the position. In ballooning, however, continues to be used exclusively hydrogen, helium as a filling would be far too expensive for gas balloons.
Helium as the second lightest element has ~ 4.0 u though four times the atomic mass, but since it exists as a noble gas in the form of atoms and not of diatomic molecules, it has after Avogadro's law with 0.1785 kg/m3 only twice as high density, such as hydrogen. Furthermore, since not the absolute density, but the difference to the air density is critical to the buoyancy, a helium filling produces only about 8% less lift than a hydrogen filling.
Both helium and hydrogen have to diffuse the property of many substances ( balloon envelope ). It may also happen that gas must be vented to the buoyancy compensation. With constantly filled balloons or airships, therefore, a small part of the gas must be replaced at regular intervals.
With one cubic meter of hydrogen can be a static lift of 1.203 kg, produce a lift of 1.1145 kg with a cubic meter of helium; but the values only under normal conditions. At some level, there is a lower air pressure (see barometric formula ), which requires for the same buoyant force supporting a larger volume of gas ( at the same load, however, the gas mass ).
From the given values is obtained as generous rule of thumb: To unlock a mass of one kilogram with balloon buoyancy, about one cubic meter carrier gas is needed, according to a gram a liter.
Earlier also the most easily available and inexpensive coal gas was used as carrier gas. Here, however, had to be taken into account in addition to the disadvantage of a much lower buoyancy of the fire hazard and toxicity. Since the conversion of the public gas supply to natural gas is no more illuminating gas available.
Above 100 ° C is as carrier gas and superheated steam is available, the ( molecular mass = 18) per volume of gas is about twice as much lift generated as the same warm air, and so after all, almost three-quarters of that of helium or hydrogen. In 2006, the scaled model was presented by Heissdampfaerostat HeiDAS UH in Germany. At a steam temperature of 150 ° C. Here, a lift of 735 grams / cubic meter was reached. The price for this service is paid for by exceptional materials for the shell material is steam resistant as stainless steel, but light as plastic. Water vapor is the most effective non-flammable lifting gas, which is not threatened by resource scarcity.
Since the helium deposits are limited and the gas is increasingly scarce and expensive due to rising consumption, one is in the balloon and airship technology gone over hydrogen and helium in a given volume ratio to mix with each other. This gas mixture then has a higher load capacity than helium alone, but the other hand is cheaper and on the other hand, in contrast to the hydrogen carrier gas inert and non-flammable ( inert).
- Airship Technology