Direction: In a simple Brayton cycle, the pressure ratio is 8 and temperature at the entrance of compressor and turbine are 300 K and 1400 K, respectively. Both compressor and gas turbine have isentropic efficiencies equal to 80%. For the gas, assume a constant value of cp (specific heat at constant pressure) equal to 1 kJ/kgK and ratio of specific heats as 1.4. Neglect changes in kinetic and potential energies.
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The thermal efficiency of the cycle in percentage (%) is
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- 24.8
- 38.6
- 44.8
- 53.1
Correct Option: A
| T4 = | = 772.9K | 8.2857 |
| ηT = | ⇒ 0.8 = | T3 - T4 | 1400 - 772.9 |
| ηcycle = | Qs |
| = | T3 - T2' |
| ηcycle= | 1400 - 604.3 |
= .248 or 24.8%
