Fuel cell performance increases with reactant gas pressure; therefore, many fuel cell systems include an air compressor that increases inlet air pressure to 2 to 4 times the ambient atmospheric pressure. For transportation applications, the compressor should be at least 75% efficient. In some cases, an expander is also included to recover electricity from high-pressure exhaust gas. The expander efficiency should be at least 80%.

Centrifugal fans are widely used in ventilation, dust removal and cooling of factories, mines, tunnels, cooling towers, vehicles, ships and buildings; ventilation and induction of boilers and industrial furnaces; cooling and cooling of air conditioning equipment and household appliances Ventilation; drying and selection of grain; wind tunnel wind source and inflation and propulsion of hovercraft, etc. The centrifugal fan is based on the principle of converting kinetic energy into potential energy, using the high-speed rotating impeller to accelerate the gas, then decelerates, changes the flow direction, and converts kinetic energy into potential energy (pressure).