Psychrometrics application: Adding water vapour to the air in an enclosed space causes a gain primarily in which component of heat content?

Introduction / Context:
In HVAC processes such as humidification, we often distinguish between sensible heat (associated with temperature change) and latent heat (associated with moisture phase change). Understanding which component changes helps size coils, humidifiers, and energy requirements.

Given Data / Assumptions:

• Closed or controlled air volume is considered.
• Water vapour is added (e.g., steam injection or evaporative humidifier).
• No chemical reactions occur in the air.

Concept / Approach:
When moisture is added, the air’s humidity ratio increases. The energy tied to vaporizing water is latent heat. Even if the dry-bulb temperature changes slightly during humidification, the defining energy gain is latent in nature because it accompanies the phase change of water to vapour.

Step-by-Step Solution:

Verification / Alternative check:
On a psychrometric chart, humidification typically moves the state toward higher humidity ratio; enthalpy rises largely due to latent component unless steam is superheated and also adds sensible heat.

Why Other Options Are Wrong:
Sensible heat dominates when only temperature changes without phase change. Chemical, nuclear, and electrical terms are unrelated to simple humidification of air.

Common Pitfalls:
Confusing relative humidity (a ratio) with humidity ratio; and assuming any temperature rise means “sensible heat only.” In steam injection, both sensible and latent may rise, but the defining component is latent.

Final Answer:
Latent heat