Moist air properties: The wet-bulb temperature is a practical indicator of the moisture content (humidity) of air.

Introduction / Context:
Wet-bulb temperature (WBT) reflects the adiabatic saturation process and is widely used in HVAC, meteorology, and cooling tower design to infer humidity levels and evaporative cooling potential.

Given Data / Assumptions:

• Air at near-atmospheric pressure.
• Psychrometric relationships hold (Dalton’s law approximation).
• WBT measured with adequate air velocity over a wetted wick.

Concept / Approach:
WBT depends on both dry-bulb temperature and moisture content. For a fixed DBT, higher humidity yields a higher WBT (closer to DBT). Conversely, drier air produces more evaporative cooling at the wick, lowering the WBT. Thus, WBT is a practical indicator of air moisture content.

Step-by-Step Solution:

Verification / Alternative check:
Using a psychrometric chart or equations, plot points with constant DBT and increasing humidity ratio; WBT values increase monotonically.

Why Other Options Are Wrong:

• “Disagree” is incorrect because WBT is standard for indicating humidity.
• “Only true at 0% RH” and “Only true at 100% RH” misunderstand the continuous relationship; WBT indicates humidity across the full range.

Common Pitfalls:
Equating WBT directly with humidity ratio; WBT is an indicator that must be interpreted with DBT or charts for exact values.

Final Answer:
Agree