Subtopic: Psychrometry – properties of air-water vapour mixture
Question Statement:
Dry bulb and wet bulb temperatures of air fed into a dryer are found to be 60 °C and 35 °C respectively. Saturation humidity at wet bulb temperature is 0.0365 kg H₂O kg dry air⁻¹. If specific heat capacities of dry air and water vapour are 1.008 and 1.915 kJ kg⁻¹K⁻¹ respectively and latent heat of vaporization at wet bulb temperature is 2.42 MJ kg⁻¹ then humidity ratio of air is
Options:
(A) 0.0193 kg H₂O kg dry air⁻¹
(B) 0.0225 kg H₂O kg dry air⁻¹
(C) 0.0256 kg H₂O kg dry air⁻¹
(D) 0.0275 kg H₂O kg dry air⁻¹
Official Answer Key:
C
Step-by-Step Solution & Explanation
Psychrometric (wet-bulb) energy balance: H = [H_s·λ_wb − c_pda(T_db−T_wb)] / [λ_wb + c_pv(T_db−T_wb)]. H = [0.0365×2420 − 1.008×25] / [2420 + 1.915×25] = [88.33−25.2]/[2420+47.9] = 63.13/2467.9 = 0.0256 kg/kg dry air.
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