Subtopic: Psychrometry – properties of air-water vapour mixture
Question Statement:
Vegetable seeds are stored at absolute temperature of 320 K and relative humidity of 20%. If Henderson equation for equilibrium relationship is valid for this case where the values of constants C and n are 6.5 × 10⁻⁶ and 1.8 respectively, the equilibrium moisture content of the seeds will be
Options:
(A) 5.6%
(B) 10.2%
(C) 13.4%
(D) 20.5%
Official Answer Key:
C
Step-by-Step Solution & Explanation
Henderson's equation: 1 − RH = exp(−C·T·Meⁿ) ⟹ Meⁿ = −ln(1−RH)/(C·T). −ln(1−0.20) = −ln(0.80) = 0.2231. C·T = 6.5×10⁻⁶ × 320 = 2.08×10⁻³. Meⁿ = 0.2231/2.08×10⁻³ = 107.3. Me = 107.3^(1/1.8) = 107.3^0.5556 = 13.43. With C and n calibrated for Me expressed directly as a percentage figure (as is standard for Henderson-model constants quoted this way), Me ≈ 13.4%, matching option (C).
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