Liquid hydrogen is the liquid state of the element
hydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. Hydrogen is found naturally in the
molecularA molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
H
2 form.
To exist as a liquid, H
2 must be pressurized above and cooled below hydrogen's
Critical pointIn physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions at which a phase boundary ceases to exist...
. However, for hydrogen to be in a full liquid state without boiling off, it needs to be cooled to 20.28 K (−423.17 °F/−252.87°C) while still pressurized. One common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is typically used as a concentrated form of
hydrogen storageHydrogen storage describes the methods for storing H2 for subsequent use. The methods span many approaches, including high pressures, cryogenics, and chemical compounds that reversibly release H2 upon heating...
. As in any gas, storing it as liquid takes less space than storing it as a gas at normal temperature and pressure, however the liquid density is very low compared to other common fuels. Once liquefied it can be maintained as a liquid in pressurized and thermally insulated containers.
Liquid hydrogen consists of
99.79% parahydrogen, 0.21% orthohydrogenMolecular hydrogen occurs in two isomeric forms, one with its two proton spins aligned parallel , the other with its two proton spins aligned antiparallel...
.
History
1756 – The first documented public demonstration of artificial
refrigerationRefrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
by
William CullenWilliam Cullen FRS FRSE FRCPE FPSG was a Scottish physician, chemist and agriculturalist, and one of the most important professors at the Edinburgh Medical School, during its heyday as the leading center of medical education in the English-speaking world.Cullen was also a central figure in the...
,
Gaspard MongeGaspard Monge, Comte de Péluse was a French mathematician, revolutionary, and was inventor of descriptive geometry. During the French Revolution, he was involved in the complete reorganization of the educational system, founding the École Polytechnique...
liquefied the first gas producing liquid
sulfur dioxideSulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
in 1784.
Michael FaradayMichael Faraday, FRS was an English chemist and physicist who contributed to the fields of electromagnetism and electrochemistry....
liquefied ammonia to cause cooling,
Oliver EvansOliver Evans was an American inventor. Evans was born in Newport, Delaware to a family of Welsh settlers. At the age of 14 he was apprenticed to a wheelwright....
designed the first closed circuit refrigeration machine in 1805,
Jacob PerkinsJacob Perkins was an Anglo-American inventor, mechanical engineer and physicist. Born in Newburyport, Massachusetts, Perkins was apprenticed to a goldsmith...
patented the first refrigerating machine in 1834 and
John GorrieJohn Gorrie , physician, scientist, inventor, and humanitarian, is considered the father of refrigeration and air conditioning. He was born on the Island of Nevis to Scottish parents on October 3, 1802, and spent his childhood in South Carolina...
patented his mechanical refrigeration machine in 1851 in the US to make ice to cool the air, Siemens introduced the Regenerative cooling concept in 1857,
Carl von LindeProfessor Doctor Carl Paul Gottfried von Linde was a German engineer who developed refrigeration and gas separation technologies...
patented equipment to liquefy air using tile
Joule Thomson expansion processIn thermodynamics, the Joule–Thomson effect or Joule–Kelvin effect or Kelvin–Joule effect describes the temperature change of a gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment. This procedure is called a...
and
regenerative coolingRegenerative cooling in rockets is where some or all of the propellant is passed through tubes, channels or otherwise in a jacket around the combustion chamber or nozzle to cool the engine because the fuel in particular and sometimes the oxidizer are good coolants...
in 1876, in 1885
Zygmunt Florenty WróblewskiZygmunt Florenty Wróblewski was a Polish physicist and chemist.-Life:Wróblewski was born in Grodno . He studied at Kiev University. After a six-year exile for participating in the January 1863 Uprising against Imperial Russia, he studied in Berlin and Heidelberg...
published hydrogen's critical temperature as 33 K; critical pressure, 13.3 atmospheres; and boiling point, 23 K.
HydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
was liquefied for the first time by
James DewarSir James Dewar FRS was a Scottish chemist and physicist. He is probably best-known today for his invention of the Dewar flask, which he used in conjunction with extensive research into the liquefaction of gases...
in 1898 by using
regenerative coolingRegenerative cooling in rockets is where some or all of the propellant is passed through tubes, channels or otherwise in a jacket around the combustion chamber or nozzle to cool the engine because the fuel in particular and sometimes the oxidizer are good coolants...
and his invention, the
vacuum flaskA vacuum flask is an insulating storage vessel which keeps its contents hotter or cooler than its surroundings. Invented by Sir James Dewar in 1892, the vacuum flask consists of two flasks, placed one within the other and joined at the neck...
. The first synthesis of the stable isomer form of liquid hydrogen, parahydrogen was achieved by
Paul HarteckPaul Karl Maria Harteck was a German physical chemist. He was arrested by the allied British and American Armed Forces and incarcerated at Farm Hall for six months in 1945 under Operation Epsilon.-Education:Harteck studied chemistry at the University of Vienna and the Humboldt University of Berlin...
and
Karl Friedrich Bonhoeffer-Life:Born in Breslau, he was an older brother of martyred theologian Dietrich Bonhoeffer.Bonhoeffer studied from 1918 in Tübingen and Berlin, finishing his PhD in 1922 in Berlin with Walther Nernst. From 1923 to 1930 he was an assistant with Fritz Haber at Kaiser Wilhelm Institute for Physical...
in 1929.
Spin isomers of hydrogen
Room temperature hydrogen consists mostly of the orthohydrogen form. After production, liquid hydrogen is in a metastable state and must be converted into the
parahydrogen isomerMolecular hydrogen occurs in two isomeric forms, one with its two proton spins aligned parallel , the other with its two proton spins aligned antiparallel...
form to avoid the
exothermic reactionAn exothermic reaction is a chemical reaction that releases energy in the form of light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...
that occurs when it changes at low temperatures, this is usually performed using a catalyst like ferric oxide,
activated carbonActivated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...
, platinized asbestos, rare earth metals, uranium compounds,
chromic oxide, or some nickel compounds.
Uses
It is a common liquid rocket fuel for
rocketSpacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
applications. In most
rocket engineA rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
s fueled by liquid hydrogen, it first cools the nozzle and other parts before being mixed with the oxidizer (usually
liquid oxygenLiquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
(LOX)) and burned to produce water with traces of
ozoneOzone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
and
hydrogen peroxideHydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
. Practical H2/O2 rocket engines run fuel-rich so that the exhaust contains some unburned hydrogen. This reduces combustion chamber and nozzle erosion. It also reduces the molecular weight of the exhaust that can actually increase
specific impulseSpecific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...
despite the incomplete combustion.
Liquid hydrogen can be used as the fuel storage in an
internal combustion engineThe internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
or
fuel cellA fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...
. Various submarines (
Type 212 submarineThe German Type 212 class, also Italian Todaro class, is a highly advanced design of non-nuclear submarine developed by Howaldtswerke-Deutsche Werft AG and Fincantieri S.p.a. for the German and Italian Navy. It features diesel propulsion and an additional air-independent propulsion system using...
,
Type 214 submarineThe Type 214 is a diesel-electric submarine developed by Howaldtswerke-Deutsche Werft GmbH . It features diesel propulsion with an air-independent propulsion system using Siemens polymer electrolyte membrane hydrogen fuel cells...
) and concept
hydrogen vehicleA hydrogen vehicle is a vehicle that uses hydrogen as its onboard fuel for motive power. Hydrogen vehicles include hydrogen fueled space rockets, as well as automobiles and other transportation vehicles...
s have been built using this form of hydrogen (see
DeepCThe DeepC is a hydrogen-fueled Autonomous Underwater Vehicle , power-assisted by an electric motor that gets its electricity from a fuel cell. It debuted in 2004...
,
BMW H2RThe BMW H2R is one of the first of a new breed of racecars adapted to run on liquid hydrogen fuel. Conceived and developed in the relatively short time of 10 months under the direction of Dr...
). Due to its similarity, builders can sometimes modify and share equipment with systems designed for
LNGLiquefied natural gas or LNG is natural gas that has been converted temporarily to liquid form for ease of storage or transport....
. However, because of the lower volumetric energy, the hydrogen volumes needed for combustion are large. Unless LH2 is injected instead of gas, hydrogen-fueled piston engines usually require larger fuel systems. Unless direct injection is used, a severe gas-displacement effect also hampers maximum breathing and increases pumping losses.
Liquid hydrogen is also used to cool neutrons to be used in neutron scattering. Since neutrons and hydrogen nuclei have similar masses, kinetic energy exchange per interaction is maximum (
elastic collisionAn elastic collision is an encounter between two bodies in which the total kinetic energy of the two bodies after the encounter is equal to their total kinetic energy before the encounter...
).
Properties
The byproduct of its combustion with oxygen alone is water vapor (although if its combustion is with oxygen and nitrogen it can form toxic chemicals), which can be cooled with some of the liquid hydrogen. Since water is considered harmless to the environment, an engine burning it can be considered "zero emissions." Liquid hydrogen also has a much higher
specific energySpecific energy is defined as the energy per unit mass. Common metric units are J/kg. It is an intensive property. Contrast this with energy, which is an extensive property. There are two main types of specific energy: potential energy and specific kinetic energy. Others are the gray and sievert,...
than gasoline, natural gas, or diesel.
The density of liquid hydrogen is only 70.99 g/L (at 20
KThe kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
), a
relative densityRelative density, or specific gravity, is the ratio of the density of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water...
of just 0.07. Although the specific energy is around twice that of other fuels, this gives it a remarkably low volumetric
energy densityEnergy density is a term used for the amount of energy stored in a given system or region of space per unit volume. Often only the useful or extractable energy is quantified, which is to say that chemically inaccessible energy such as rest mass energy is ignored...
, many fold lower.
Liquid hydrogen requires cryogenic storage technology such as special thermally insulated containers and requires special handling common to all
cryogenic fuelCryogenic fuels are fuels that require storage at extremely low temperatures in order to maintain them in a liquid state. Cryogenic fuels most often constitute liquefied gases such as liquid hydrogen....
s. This is similar to, but more severe than
liquid oxygenLiquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
. Even with thermally insulated containers it is difficult to keep such a low temperature, and the hydrogen will gradually leak away (typically at a rate of 1% per day). It also shares many of the same
safety issuesHydrogen safety covers the safe use and handling of hydrogen. Hydrogen poses unique challenges due to its ease of leaking, low-energy ignition, wide range of combustible fuel-air mixtures, buoyancy, and its ability to embrittle metals that must be accounted for to ensure safe operation...
as other forms of hydrogen, as well as being cold enough to liquefy (and possibly solidify) atmospheric oxygen which can be an explosion hazard.
See also
- Hydrogen safety
Hydrogen safety covers the safe use and handling of hydrogen. Hydrogen poses unique challenges due to its ease of leaking, low-energy ignition, wide range of combustible fuel-air mixtures, buoyancy, and its ability to embrittle metals that must be accounted for to ensure safe operation...
- Compressed hydrogen
Compressed hydrogen is the gaseous state of the element hydrogen kept under pressure. Compressed hydrogen in hydrogen tanks at 350 bar and 700 bar is used for mobile hydrogen storage in hydrogen vehicles...
- Cryo-adsorption
Cryo-adsorption is a method used for hydrogen storage where gaseous hydrogen at cryogenic temperatures is physically adsorbed on porous material, mostly activated carbon. The achievable storage density is between liquid hydrogen storage systems and compressed hydrogen storage systems.-External...
- Expansion ratio
The expansion ratio of a liquefied and cryogenic substance is the volume of a given amount of that substance in liquid form compared to the volume of the same amount of substance in gaseous form, at a given temperature and pressure....
- Gasoline gallon equivalent
- industrial gas
Industrial gas is a group of gases that are commercially manufactured and sold for uses in other applications. These gases are mainly used in an industrial processes, such as steelmaking, oil refining, medical applications, fertilizer, semiconductors, etc.,...
- Slush hydrogen
Slush hydrogen is a combination of liquid hydrogen and solid hydrogen at the triple point with a lower temperature and a higher density than liquid hydrogen. It is formed by bringing liquid hydrogen down to nearly the melting point that increases density by 16–20% as compared to liquid hydrogen...
- Solid hydrogen
Solid hydrogen is the solid state of the element hydrogen, achieved by decreasing the temperature below hydrogen's melting point of 14.01 K . It was collected for the first time by James Dewar in 1899 and published with the title "Sur la solidification de l'hydrogène" in the Annales de Chimie et...
- Metallic hydrogen
Metallic hydrogen is a state of hydrogen which results when it is sufficiently compressed and undergoes a phase transition; it is an example of degenerate matter. Solid metallic hydrogen is predicted to consist of a crystal lattice of hydrogen nuclei , with a spacing which is significantly smaller...
- Hydrogen infrastructure
A hydrogen infrastructure is the infrastructure of pipes and stations for distribution and sale of hydrogen fuel.-Hydrogen pipeline transport:Hydrogen pipeline transport is a transportation of hydrogen through a pipe as part of the hydrogen infrastructure...
- Liquid hydrogen tank car
A liquid hydrogen tank car, also called liquid hydrogen tank wagon or liquid hydrogen tanker wagon is a railroad tank car designed to carry cryogenic liquid hydrogen...
- Liquid hydrogen tanktainer
A liquid hydrogen tank-tainer also known as a liquid hydrogen tank container is a specialized type of container designed to carry cryogenic liquid hydrogen on standard intermodal equipment...
- Liquid hydrogen tank truck
- Liquefaction of gases
Liquefaction of gases includes a number of phases used to convert a gas into a liquid state. The processes are used for scientific, industrial and commercial purposes. Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as carbon dioxide, require...