Project ForgeThermodynamics
First Law of Thermodynamics
GATE 2008
Hard
Moist air at 100 kPa is compressed to 500 kPa and then cooled to 35°C in an aftercooler. The air at the aftercooler exit is unsaturated and becomes just saturated at the exit. The saturation pressure of water at 35°C is 5.628 kPa. The partial pressure of water vapour (kPa) in the moist air entering the compressor is closest to
- A0.57
- 1.13
- C2.26
- D4.52
Explanation
The humidity ratio ω is unchanged from inlet to aftercooler exit (no moisture is removed). At exit: ω=0.622Pv/(P-Pv)=0.622(5.628)/(500-5.628)≈0.00708. At inlet (P=100kPa): solve 0.622Pv_in/(100-Pv_in)=0.00708 ⟹ Pv_in≈1.13 kPa.
Source: GATE ME 2008 (2008)
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