Alternative method of estimating divergence ratio

We may observe, first of all, that no additional expansion will take place at the nozzle outlet if the pressure ratio is above the nozzle s lower critical pressure ratio, (P crin)lPot- The large size of the exhaust chamber will have no effect on the measured efficiency when 

We may estimate rjnoc for the purposes of these equations from the measured efficiency at low pressure ratios, and hence find ntoc- As discussed at the end of Section A6.1, the local and stagnation temperatures will be almost identical, so that TqtITo  

We know from calculus that the minimum value of efficiency occurs when 

Carrying out the necessary differentiation of equations (14.106) and (A6.13) gives the condition  

Equation (A6.15) relates the divergence ratio, A /A to the pressure ratio at minimum nozzle efficiency. 

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