Cooling coil performance: effect of air velocity on by-pass factor As the face velocity of air through a cooling coil increases, how does the coil's by-pass factor typically change? Choose the correct trend.
Mechanical Engineering
Heat Transfer, Refrigeration and Air Conditioning
Difficulty: Easy
Choose an option
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AIncreases with increase in air velocity
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BDecreases with increase in air velocity
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CRemains unchanged with air velocity
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DMay increase or decrease depending on inlet-air condition only
Answer
Correct Answer: Increases with increase in air velocity
Explanation
Given/DefinitionsBy-pass factor (BPF) quantifies the fraction of air that effectively "bypasses" ideal contact with the coil surface (i.e., leaves above apparatus dew-point).
Concept/ApproachHigher air velocity reduces contact time and reduces heat/mass transfer effectiveness, so a larger fraction of air leaves closer to the inlet state → higher BPF.
ThereforeBPF increases as air velocity increases.