A nozzle is said to be chocked when

Explanation:

Convergent-divergent nozzle:

• Convergent-Divergent nozzles are used to increase the flow of gas to supersonic speeds (as in the case of rockets).
• Their cross-sectional area first decreases and then increases. The area where the diameter is minimum is called the throat.
• As the gas enters the converging section, its velocity increases, considering the mass flow rate to be constant.
• As the gas passes through the throat, it attains sonic velocity (Mach number = 1).
• As the gas passes through the divergent nozzle, the velocity increases to supersonic (Mach number >1).

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• The flow rate is maximum for a given nozzle if the flow is sonic at the throat. This condition is achieved by managing the back-pressure. If the mass flow rate is reached the maximum value at the throat then the flow is called choked flow.
• For the compressible fluid flow, the Mach number is an important dimensionless parameter. On the basis of the Mach number, the flow is defined.
• Choked flow is a limiting condition where the mass flow will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed.
• For chocked flow in the convergent-divergent nozzle, the Mach number at the throat is equal to 1 and the pressure at the throat is equal to the critical pressure.
• Critical pressure ratio for a choked nozzle:

where p* is the critical pressure and p0 is the inlet pressure.