Psychrometrics relation: dew-point vs wet-bulb as relative humidity decreases As the relative humidity of moist air decreases, how does the dew-point temperature compare to the wet-bulb temperature? Choose the correct relation.
Mechanical Engineering
Heat Transfer, Refrigeration and Air Conditioning
Difficulty: Easy
Choose an option
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AGreater than the wet-bulb temperature
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BEqual to the wet-bulb temperature
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CLess than the wet-bulb temperature
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DUnrelated/independent of the wet-bulb temperature
Answer
Correct Answer: Less than the wet-bulb temperature
Explanation
Given conceptFor unsaturated air: Tdew ≤ Twb ≤ Tdb. As relative humidity (RH) drops, the mixture is further from saturation, so Tdew falls away from Twb.
ReasoningLower RH → lower vapor partial pressure → lower Tdew. The wet-bulb temperature decreases too, but not as much; thus Tdew stays below Twb.
Common pitfallConfusing Tdew with Twb; they are equal only at saturation (RH = 100%).
Final AnswerLess than the wet-bulb temperature.