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Thermodynamics
First Law of Thermodynamics
GATE 2010
Medium

A moist air sample has dry bulb temperature of 30°C and specific humidity of 11.5 g water vapour per kg dry air. Assume molecular weight of air as 28.93. If the saturation vapour pressure of water at 30°C is 4.24 kPa and the total pressure is 90 kPa, then the relative humidity (in %) of the air sample is

  • A50.5
  • 38.5
  • C56.5
  • D68.5

Explanation

ω=0.622·Pv/(P-Pv). 0.0115=0.622·Pv/(90-Pv) ⟹ Pv≈1.634 kPa. RH=Pv/Pvs=1.634/4.24≈38.5%.

Source: GATE ME 2010 (2010)

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