HVAC and psychrometrics — In an evaporative cooling process (cooling plus humidification), which heat terms are added or removed from the air stream?

Introduction:Evaporative cooling is a common air-conditioning strategy in dry climates. It cools air by evaporating water directly into the airstream. Understanding the energy terms clarifies why air temperature drops while humidity rises during the process.

Given Data / Assumptions:

• Unsaturated incoming air contacts liquid water; no external heat added.
• Evaporation uses energy drawn from the air stream.
• Adiabatic assumption for the control volume (no heat exchange with surroundings).

Concept / Approach:

Water evaporation requires latent heat of vaporization. In an adiabatic saturator, that energy is supplied by the air's sensible enthalpy, lowering dry-bulb temperature while increasing moisture content (latent enthalpy). Thus, the net effect is removal of sensible heat and addition of latent heat to the air, with total enthalpy approximately conserved (neglecting small losses).

Step-by-Step Solution:

Verification / Alternative check:

On a psychrometric chart, the process line approximates a constant enthalpy path moving toward saturation: dry-bulb decreases, humidity ratio increases.

Why Other Options Are Wrong:

A and D: These claim sensible heat is added, opposite to observed cooling. C: Latent heat is not removed; it is introduced via added vapor. E: Changes clearly occur in both sensible and latent components.

Common Pitfalls:

Confusing evaporative cooling with sensible cooling over a coil, where both sensible and latent may be removed together (dehumidification).

Final Answer:

Sensible heat is removed and latent heat is added