Choked flow

Summary

Choked flow is the state of a compressible flow through a passage in which the flow at the narrowest section reaches the speed of sound. Once this happens, the mass flow rate has reached its largest possible value for the given upstream conditions. Lowering the pressure downstream then no longer increases the flow, because the information about the downstream pressure cannot travel upstream through a sonic section. Choking limits the flow through valves, nozzles and orifices, and it is also caused by friction or heating in a duct of constant area.