At 60°C dry-bulb temperature, saturated water-vapor pressure is 20 kPa and relative humidity 20%. Atmospheric pressure is 101.325 kPa. Molecular masses of water and dry air are 18.02 and 28.97 g/mol. Find the nearest absolute humidity ratio in kg water/kg dry air.
Vapor partial pressure is $p_v=\phi p_{vs}=.20(20)=4$ kPa. The humidity ratio is $w=(M_w/M_a)p_v/(P-p_v)=(18.02/28.97)4/(101.325-4)=0.02556$ kg/kg. The nearest choice is **0.026,A**. This uses the mass-of-water per mass-of-dry-air convention intended by the options.
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