Psychrometric limit: At 100% relative humidity, the wet-bulb temperature is __________ the dry-bulb temperature.
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Athe same as
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Blower than
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Chigher than
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Dunrelated to
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Ealways 0°C
Answer
Correct Answer: the same as
Explanation
Introduction / Context:Wet-bulb temperature (WBT) reflects evaporative cooling potential. At saturation (RH = 100%), air cannot accept more moisture, so evaporation from a wetted wick ceases and WBT converges to dry-bulb temperature (DBT).
Given Data / Assumptions:
- Air–water vapour mixture at atmospheric pressure.
- Thermometer bulb properly wetted and ventilated.
- State point lies on the saturation curve (RH = 100%).
Concept / Approach:At saturation, the partial pressure of water vapour equals the saturation pressure at that temperature. No net evaporation occurs from the wick, eliminating evaporative cooling. Therefore, WBT = DBT at the saturation state.
Step-by-Step Solution:
RH = 100% implies state on the saturation line.Evaporation rate from the wick → 0; latent cooling → 0.Thermometer stabilizes at the ambient dry-bulb temperature.Thus WBT equals DBT.Verification / Alternative check:On a psychrometric chart, lines of constant WBT meet the saturation curve exactly at the same point as DBT, confirming equality at RH = 100%.
Why Other Options Are Wrong:“Lower” or “higher” occur only for unsaturated air; “unrelated” and “always 0°C” are physically incorrect.
Common Pitfalls:Assuming some evaporation persists at 100% RH; in ideal measurement, none does.
Final Answer:the same as