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GATE 2021 ME (ME2) – Question 40

Thermal Engineering Applications · Psychrometry and air-conditioning · 2 marks · Multiple choice

Ambient pressure, temperature, and relative humidity at a location are 101 kPa, 300 K, and 60%, respectively. The saturation pressure of water at 300 K is 3.6 kPa. The specific humidity of ambient air is _____ g/kg of dry air.

  1. 21.4
  2. 35.1
  3. 21.9
  4. 13.6

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Show answer and explanation

Correct answer: (D) 13.6

Explanation

Vapour partial pressure is $p_v=0.6(3.6)=2.16$ kPa. Humidity ratio is $w=0.622p_v/(P-p_v)$.

Thus w=0.622(2.16)/(101−2.16)=0.0135929 kg/kg, or **13.6 g/kg (D)**. Relative humidity is not the humidity ratio.