Just as for isothermal flow, this is an implicit expression for the "choke pressure'' (P*) as a function of the upstream pressure (P1), the loss coefficients (J] Kf), and the isentropic exponent (k), which is most easily solved by iteration. It is very important to realize that once the pressure at the end of the pipe falls to P*2 and choked flow occurs, all of the conditions within the pipe (G = G*, P2 = P2, etc.) will remain the same regardless of how low the pressure outside the end of the pipe falls. The pressure drop within the pipe (which determines the flow rate) is always P1 — P* when the flow is choked.

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