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Gas flow through a nozzle

Gas flow through a nozzle The gas flow through a nozzle depends on the pressure ratio on respective sides of the nozzle. If the pressure after the nozzle is lowered the flow increases, however, only until its pressure before the nozzle is approximately double so high. A further reduction of the pressure after the opening does not bring about an increase in flow. This is the critical pressure ratio and it is dependent on the gas's isentropic exponent (k). The critical pressure ratio occurs when the flow velocity is equal to the sonic velocity in the nozzle's narrowest section. The flow becomes supercritical if the pressure after the nozzle is reduced further, under the critical value. The relation for the flow through the nozzle is: