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Liquid hydrogen is typically used as a concentrated form of hydrogen storage. 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 for some time in thermally insulated containers. [6]
At low temperatures and at pressures up to around 400 GPa (3,900,000 atm), hydrogen forms a series of solid phases formed from discrete H 2 molecules. Phase I occurs at low temperatures and pressures, and consists of a hexagonal close-packed array of freely rotating H 2 molecules.
Since "normal" room-temperature hydrogen is a 3:1 ortho:para mixture, its molar residual rotational energy at low temperature is (3/4) × 2Rθ rot ≈ 1091 J/mol, [citation needed] which is somewhat larger than the enthalpy of vaporization of normal hydrogen, 904 J/mol at the boiling point, T b ≈ 20.369 K. [10] Notably, the boiling points of ...
At room temperature or warmer, equilibrium hydrogen gas contains about 25% of the para form and 75% of the ortho form. [30] The ortho form is an excited state, having higher energy than the para form by 1.455 kJ/mol, [31] and it converts to the para form over the course of several minutes when cooled to low temperature. [32]
At room temperature, the diffusivity is very low, and the hydrogen is trapped in the HGM. The disadvantage of HGMs is that to fill and outgas hydrogen effectively the temperature must be at least 300 °C which significantly increases the operational cost of HGM in hydrogen storage. [ 116 ]
Even with thermally insulated containers it is difficult to keep such a low temperature, and the hydrogen will gradually leak away. Typically it will evaporate at a rate of 1% per day. [1] [42] The main danger with cryogenic hydrogen is what is known as BLEVE (boiling liquid expanding vapor explosion).
Helium and hydrogen are two gases whose Joule–Thomson inversion temperatures at a pressure of one atmosphere are very low (e.g., about 40 K, −233 °C for helium). Thus, helium and hydrogen warm when expanded at constant enthalpy at typical room temperatures.
The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. [1]