Psychrometrics: For a fixed dry-bulb temperature, as relative humidity __________, the wet-bulb temperature will increase.

Introduction / Context:
Wet-bulb temperature (WBT) is a key indicator of the moisture content and evaporative cooling potential of air. It reflects the adiabatic saturation process and is central to cooling tower and comfort calculations.

Given Data / Assumptions:

• Dry-bulb temperature (DBT) is held constant.
• Relative humidity (RH) varies between 0 and 100%.
• Pressure is near atmospheric.

Concept / Approach:
At fixed DBT, higher RH means the air is closer to saturation, so there is less capacity to absorb additional moisture via evaporation. Because WBT is the equilibrium temperature reached by evaporative cooling, as RH increases, the gap DBT − WBT narrows, implying WBT rises toward DBT.

Step-by-Step Solution:

Verification / Alternative check:
Read any psychrometric chart at fixed DBT: moving along a vertical DBT line toward higher RH moves upward along constant WBT lines, confirming higher WBT.

Why Other Options Are Wrong:

• Decreases: opposite of chart behavior.
• Remains constant: only true if DBT and humidity ratio both fixed.
• Non-monotonic change: no such trend exists under these conditions.

Common Pitfalls:
Confusing WBT with dew point temperature; dew point increases strongly with humidity ratio, whereas WBT approaches DBT as RH approaches 100%.

Final Answer:
increases