Psychrometric limit: At 100% relative humidity, the wet-bulb temperature is __________ the dry-bulb temperature.

Difficulty: Easy

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

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