Critical pressure ratio for choked flow in a nozzle Let p1 be the inlet (stagnation) pressure and p2 the throat static pressure at choking. Express the critical pressure ratio (p2/p1) in terms of the ratio of specific heats γ. Choose the correct expression.
Mechanical Engineering
Steam Nozzles and Turbines
Difficulty: Medium
Choose an option
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A(2/(γ + 1))^(γ/(γ − 1))
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B(γ + 1)/(γ − 1)
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C(2γ/(γ + 1))^(1/(γ − 1))
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D(γ − 1)/(γ + 1)
Answer
Correct Answer: (2/(γ + 1))^(γ/(γ − 1))
Explanation
Concept/Approach
- For isentropic flow of a perfect gas, the sonic (choked) condition at the throat gives (p2/p1)crit = (2/(γ + 1))γ/(γ − 1).
- This is derived from the energy equation and isentropic relations at Mach = 1.
Final Answer(2/(γ + 1))^(γ/(γ − 1))