Compressor in the context of "Impeller"

Liquid hydrogen (H₂(l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H₂ form.

To exist as a liquid, H₂ must be cooled below its critical point of 33 K. However, for it to be in a fully liquid state at atmospheric pressure, H₂ needs to be cooled to 20.28 K (−252.87 °C; −423.17 °F). A 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 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.

For fluid power, a working fluid is a gas or liquid that primarily transfers force, motion, or mechanical energy. In hydraulics, water or hydraulic fluid transfers force between hydraulic components such as hydraulic pumps, hydraulic cylinders, and hydraulic motors that are assembled into hydraulic machinery, hydraulic drive systems, etc. In pneumatics, the working fluid is air or another gas which transfers force between pneumatic components such as compressors, vacuum pumps, pneumatic cylinders, and pneumatic motors. In pneumatic systems, the working gas also stores energy because it is compressible. (Gases also heat up as they are compressed and cool as they expand. Some gases also condense into liquids as they are compressed and boil as pressure is reduced.)

For passive heat transfer, a working fluid is a gas or liquid, usually called a coolant or heat transfer fluid, that primarily transfers heat into or out of a region of interest by conduction, convection, and/or forced convection (pumped liquid cooling, air cooling, etc.).

In turbomachinery, degree of reaction or reaction ratio (denoted R) is defined as the ratio of the change in static pressure in the rotating blades of a compressor or turbine, to the static pressure change in the compressor or turbine stage. Alternatively it is the ratio of static enthalpy change in the rotor to the static enthalpy change in the stage.

Various definitions exist in terms of enthalpies, pressures or flow geometry of the device. In case of turbines, both impulse and reaction machines, degree of reaction is defined as the ratio of energy transfer by the change in static head to the total energy transfer in the rotor:$${\displaystyle R={\frac {\text{Isentropic enthalpy change in rotor}}{\text{Isentropic enthalpy change in stage}}}}$$

Bottled gas is a term used for substances which are gaseous at standard temperature and pressure (STP) and have been compressed and stored in carbon steel, stainless steel, aluminum, or composite containers known as gas cylinders.