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A gas turbine with air as the working fluid has an isentropic efficiency of 0.70 when operating at a pressure ratio of 3. Now, the pressure ratio of t he t ur bi ne i s i ncr eased t o 5, whi l e maintaining the same inlet conditions. Assume air as a perfect gas with specific heat ratio γ = 1.4. I f the specific work output remains the same for both the cases, the isentropic efficiency of t he t ur bi ne at t he pr essur e r at i o of 5 is___(round off to two decimal places).
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- 5
- 7
- 0.51
- 1
Correct Option: C
η = 0.7, (rρ)1 = 3
η2 =? (rρ)2 = 5
r = 1.4
(WT)1 = (WT)2
As Inlet condition same, 
Here,
| η1 = | = | ||
| T1 - T2s |
| = | |
| T1 - T2s | T1 - T2s/x |
| η1 |  | T1 - |  | = | η2 | | T1 - | | ||
| x | y |
| 0.7 | | 1 - | | = | η2 | | 1 - | | ||
| (3)2/7 | (5)2/4 |
η2 = 0.51
Hence, Isentropic efficiency of turbine is 0.51.
