CRITICAL PRESSURE RATIO

There is only one value of the ratio (p2 / p1), which produces maximum discharge from the nozzle. This ratio is called critical pressure ratio.

Where p1 = Inlet pressure.

p2 = Throat Pressure.

i) For saturated steam n = 1.135

We know that the critical pressure ratio

(p2 / p1) = (2 / (n+1))^ (n / (n-1))

(p2 / p1) = ( 2 / (1.135 +1))^ (1.135 / (1.135 -1))

Critical pressure ratio, (p2 / p1) = 0.577

ii) For Super heated steam n = 1.3

(p2 / p1) = (2 / (n+1))^ (n / (n-1))

= (2 / (1.3 -1))^ (1.3 / (1.3 -1 ))

Critical Pressure Ratio , (p2 / p1) = 0.546

iii) For gases n = 1.4

Critical Pressure ratio , p2 / p1 = ( 2 / (n+1)) ^ ( n / (n-1))

p2 / p1 = ( 2 / (1.4 + 1))^ (1.4 / (1.4 -1))

p2 / p1 = 0.5282

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