In psychrometry, what do we call the temperature indicated by a thermometer whose bulb is covered with a wetted wick and exposed to moving air?

Introduction / Context:
Wet-bulb temperature is a cornerstone concept in HVAC, meteorology, and drying processes. It reflects the combined effects of sensible heat and latent cooling due to evaporation and is essential for calculating humidity ratio, enthalpy, and equipment loads using the psychrometric chart.

Given Data / Assumptions:

• A thermometer bulb is wrapped with a wet wick (wick kept moist).
• Air stream moves across the wetted bulb to enable evaporation.
• Steady ambient pressure is assumed.

Concept / Approach:
As air flows over the wetted wick, water evaporates from the wick surface. Evaporation requires latent heat, which is drawn from the water-film/thermometer bulb, reducing its temperature. The temperature indicated after reaching equilibrium is the wet-bulb temperature. At 100% relative humidity, no net evaporation occurs and wet-bulb equals dry-bulb temperature; at lower humidity, wet-bulb is lower than dry-bulb by an amount related to moisture deficit.

Step-by-Step Solution:

Verification / Alternative check:
A sling psychrometer uses two thermometers: one dry-bulb and one wet-bulb. Their readings, along with psychrometric relations, yield humidity ratio, relative humidity, and enthalpy of moist air.

Why Other Options Are Wrong:

• Dry-bulb temperature (b) is measured with a normal thermometer unaffected by evaporation.
• Dew-point (c) is the saturation temperature at the existing vapour partial pressure, not measured by a wetted wick.
• Adiabatic saturation temperature (d) is a related theoretical construct but not the direct thermometer reading with a wick.
• Globe temperature (e) measures radiant heat effects with a black globe, not evaporation.

Common Pitfalls:
Assuming wet-bulb equals dew-point universally; they are equal only at saturation (100% RH) when both also equal dry-bulb.

Final Answer:
Wet-bulb temperature