Psychrometric processes: On a standard chart, adiabatic humidification (evaporative cooling of unsaturated air) is represented by which type of line?

Introduction / Context:
Understanding how processes plot on the psychrometric chart is crucial for sizing evaporative coolers, spray washers, and air-handling equipment. Adiabatic humidification adds moisture while air gives up sensible heat, moving toward saturation.

Given Data / Assumptions:

• Atmospheric pressure is near 1 atm.
• Water temperature approximates the entering air wet-bulb temperature.
• Heat exchange with surroundings is negligible (adiabatic).

Concept / Approach:
For adiabatic humidification, the air enthalpy remains nearly constant while humidity ratio increases and dry-bulb temperature decreases. On a psychrometric chart, constant enthalpy and constant wet-bulb lines are nearly straight slanted lines; the process thus follows an inclined path up and to the left toward the saturation curve.

Step-by-Step Solution:

Verification / Alternative check:
Compare with measured psychrometer data: states with equal wet-bulb temperature lie nearly on straight lines; evaporative cooler performance follows those lines.

Why Other Options Are Wrong:

• Horizontal implies constant humidity ratio (no moisture addition), which contradicts humidification.
• Vertical implies constant dry-bulb (pure steam injection at matched sensible heat), not adiabatic evaporative cooling.
• Curved constant-dew-point is not the evaporative path.

Common Pitfalls:
Confusing steam injection (often increases DBT) with evaporative cooling (decreases DBT); and misreading wet-bulb vs dew point lines.

Final Answer:
Inclined line (approximately straight along near-constant wet-bulb/enthalpy)