When a gas changes its state to become a fluid such as liquid hydrogen, the temperature when it occurs is called the critical point. The practical application of this conversion is to enable concentrated storage of gases in their condensed form. This gas in particular is useful as a liquefied fuel due to its flammability and the energy it carries. Support for a clean fuel economy based on this gas is growing as the technology advances.
In studying the nature and properties of gases during the nineteenth century, chemists developed the process known as regenerative cooling to change gases into their fluid state before the compact gasifier. Gaseous hydrogen, or H2, was first cooled into its fluid state, called LH2, by using a vacuum flask and regenerative cooling. A colorless fluid that liquefies at -423 Fahrenheit was the result.
Alternate structures of a molecule are known as isomers and this element occurs in two states called ortho and para. Under normal conditions, these isomers are present respectively in the ratio of 3:1. To be stable as a fluid, it must be converted to about 99 percent parahydrogen. Since this gas is highly flammable, storing it in a stable from is important to avoid an exothermic reaction, that is, a sudden burst of heat occurring at the critical point.
Storage in the liquefied state is preferable since it becomes so compressed compared to the gaseous state. A compressor that works like and resembles a jet engine is how the gas is condensed into the fluid form. By greatly expanding the surrounding area, the gas condenses and the heat is removed. Using a heat exchanging device, the gas is cooled until it reaches the critical point.
When combined with oxygen and burned to release its energy as a fuel, the waste by product is water, unlike fossil fuels which produce toxic by products. So this gas is considered to have great potential for a clean burning fuel. Stored in the fluid form, it can cool rocket engines and condense the water vapor given off before being burned as fuel.
LH2 is being considered as an alternative fuel. Used as a fuel for internal combustion engines, the liquefied form works better than its gaseous state because of its lower energy density than gasoline or natural gas. This gas is somewhat more difficult to store than some other liquefied gases due to its extremely low temperature.
Assuming the solving of some technical problems, LH2 may become the clean burning alternative energy of choice for transportation and fuel cell technology. Promising designs for autos running on this fuel are in development and some submarines are powered in this manner. Rocket engines use this burned in a fuel rich mixture that works to protect engine parts and even increase acceleration.
Liquid hydrogen is getting a close look as an important energy carrier in an economy some believe can be based on this gas as the fuel. As it does not exist in nature on Earth in large quantities, it must be produced from an energy source such as natural gas with a advanced gasifier. It is considered an energy carrier instead of energy source. But as a clean fuel for transportation and heating, it could well replace fossil fuels someday.
