Direction: In an experimental set-up, air flows between two stations P and Q adiabatically. The direction of flow depends on the pressure and temperature conditions maintained at P and Q. The conditions at station P are 150 kPa and 350 K. The temperature at station Q is 300 K. The following are the properties and relations pertaining to air:
Specific heat at constant pressure, cp = 1.005 kJ/kgK;
Specific heat at constant volume, cv = 0.718 kJ/kgK;
Characteristic gas constant, R = 0.287 kJ/kgK.
Enthalpy, h = cpT. .
Internal energy, u = cvT.
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If the air has to flow from station P to station Q, the maximum possible value of pressure in kPa at station Q is close to
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- 50
- 87
- 128
- 150
Correct Option: B
| SQ - Sp = Cvln |  | T2 |  | + Rln | | V2 | | |||
| T1 | V1 |
From perfect gas law,
| = | V1 | P2 | T1 |
| = | = 2.57 | 300 × 350 |
∴ SQ – Sp = – 0.1107 + 0.287 ln 2.57 = 0.16 kJ/kgK
