Project ForgeMoist air at 105 kPa, 30°C and 80% relative humidity flows over a cooling coil in an insulated air-conditioning duct. Saturated air exits the duct at 100 kPa and 15°C. The saturation pressures of water at 30°C and 15°C are 4.24 kPa and 1.7 kPa respectively. Molecular weight of water is 18 g/mol and that of air is 28.94 g/mol. The mass of water condensing out from the duct is __________ g/kg of dry air (round off to the nearest integer).
Explanation
Inlet: pv1=0.8×4.24=3.392 kPa, pa1=105−3.392=101.608 kPa, w1=0.622×3.392/101.608≈0.02077 kg/kg. Exit (saturated): pv2=1.7 kPa, pa2=100−1.7=98.3 kPa, w2=0.622×1.7/98.3≈0.01076 kg/kg. Condensed water = w1−w2 ≈ 0.01001 kg/kg = 10.0 g/kg dry air.
Source: GATE ME 2020 Session 2 (ME-2) (2020)
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