Psychrometrics — what decreases during sensible heating? During sensible heating of air at essentially constant moisture content, which property decreases as temperature rises?

Introduction / Context:
Sensible heating raises the dry-bulb temperature without changing the amount of water vapour in the air. Understanding which psychrometric properties increase or decrease is crucial for HVAC control.

Given Data / Assumptions:

• No moisture is added or removed (humidity ratio w constant).
• Standard atmospheric pressure; air behaves as an ideal mixture.

Concept / Approach:
Relative humidity (RH) is the ratio of the partial pressure of water vapour to the saturation pressure at the same temperature. As temperature increases at constant vapour content, saturation pressure increases strongly, so RH decreases.

Step-by-Step Solution:

Verification / Alternative check:
On the psychrometric chart, sensible heating moves horizontally to the right; constant w lines indicate RH contours dropping as temperature rises.

Why Other Options Are Wrong:
Dry-bulb temperature increases, not decreases. Specific humidity (humidity ratio) remains constant in sensible processes. Wet-bulb temperature typically increases somewhat with sensible heating at constant w, not decreases.

Common Pitfalls:
Equating RH with moisture content; RH can fall even though the actual moisture in the air is unchanged.

Final Answer:

relative humidity