Project ForgeProcess Calculations
Laws of Thermodynamics
GATE 2018
Hard
Air at 65°C dry-bulb has humidity 0.025 kg water/kg dry air. Latent heat of water at 0°C=2500 kJ/kg. Psychrometric ratio=0.95 kJ/(kg dry air)/K. Referenced to 0°C, the enthalpy (kJ/kg) of air at its adiabatic saturation temperature of 35°C is (rounded off to two decimal places)
124.25 kJ/kg(± 0.5 accepted)
Explanation
Enthalpy is conserved along an adiabatic-saturation line, so the enthalpy AT the saturation temperature equals the ORIGINAL air's enthalpy: H=Cs·T+Y·λ0=0.95×65+0.025×2500=61.75+62.5=124.25 kJ/kg (no need to separately solve for the saturation humidity at 35°C).
Source: GATE CH 2018 (2018)
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