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In aviation, however, water vapor emitted in the atmosphere contributes to global warming (to a lesser extent than CO 2). [11] Liquid hydrogen also has a much higher specific energy than gasoline, natural gas, or diesel. [12] The density of liquid hydrogen is only 70.85 kg/m 3 (at 20 K), a relative density of just 0.07. Although the specific ...
Because of the enormous density difference between water and gases (water is about 1,000 times denser than most gases), the lifting power of underwater gases is very strong. The type of gas used is largely inconsequential because the relative differences between gases is negligible in relation to the density of water.
Hydrogen gas is very rare in Earth's atmosphere (around 0.53 ppm on a molar basis [99]) because of its light weight, which enables it to escape the atmosphere more rapidly than heavier gases. However, hydrogen is the third most abundant element on the Earth's surface, [ 100 ] mostly in the form of chemical compounds such as hydrocarbons and water.
Water electrolysis is using electricity to split water into hydrogen and oxygen. As of 2020, less than 0.1% of hydrogen production comes from water electrolysis. [46] Electrolysis of water is 70–80% efficient (a 20–30% conversion loss) [47] [48] while steam reforming of natural gas has a thermal efficiency between 70 and 85%. [49]
Although molecular hydrogen has very high energy density on a mass basis, partly because of its low molecular weight, as a gas at ambient conditions it has very low energy density by volume. If it is to be used as fuel stored on board a vehicle, pure hydrogen gas must be stored in an energy-dense form to provide sufficient driving range.
The higher the energy density of the fuel, the more energy may be stored or transported for the same amount of volume. The energy of a fuel per unit mass is called its specific energy. The adjacent figure shows the gravimetric and volumetric energy density of some fuels and storage technologies (modified from the Gasoline article).
Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. [107] In the presence of sunlight, hydrogen is combined with CO 2 (absorbed from air or water) to form glucose and release oxygen. [108] All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO
The relative density of an aerostat as a whole is lower than that of the surrounding atmospheric air (hence the name "lighter-than-air"). Its main component is one or more gas capsules made of lightweight skins , containing a lifting gas (hot air, or any gas with lower density than air, typically hydrogen or helium ) that displaces a large ...