Subtopic: Psychrometry – properties of air-water vapour mixture
Question Statement:
In an effort to conserve energy, a grain dryer is being modified to reuse a part (10 m³ s⁻¹) of the exhaust airflow at 70 ºC and 30% relative humidity. This part of exhaust is mixed with 20 m³ s⁻¹ of ambient air at 30 ºC and 60% relative humidity. The absolute humidity of the mixed air will be __________. [round off to three decimal places]
Official Answer Key:
0.028 to 0.032
Step-by-Step Solution & Explanation
• Mixed absolute humidity ≈ volumetric-flow-weighted average of the two streams' humidity ratios (approximating airflow proportional to dry-air mass flow, as is standard practice when detailed humid-volume data is not separately provided):
• H_mix = (Q1·H1 + Q2·H2)/(Q1+Q2) = (10×63.35×10⁻³ + 20×16×10⁻³)/30 = (0.6335+0.320)/30 = 0.9535/30 = 0.03178
Computed value: 0.0318 (within official range 0.028–0.032)
Section 7 — Dairy and Food Engineering
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