GATE 2018 ME (ME2) – Question 54
Ambient air is at 100 kPa, dry-bulb temperature 30°C and relative humidity 60%. Water saturation pressure at 30°C is 4.24 kPa. Find specific humidity in g/kg of dry air, to two decimal places.
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Correct answer: 16.00 to 16.50
Explanation
Vapour partial pressure is $p_v=0.60(4.24)=2.544$ kPa. Humidity ratio is $$w=0.622\frac{p_v}{p-p_v}=0.622\frac{2.544}{100-2.544}=0.0162367\ \mathrm{kg/kg}.$$ Multiply by 1000: **16.24 g/kg dry air**.