Dry-bulb temperature (DBT) is defined as the temperature of air measured by a standard thermometer that is not affected by the moisture present in the air. Which option matches this definition?

Introduction / Context:
Dry-bulb temperature is the most familiar temperature measurement and is central to psychrometric analysis. It represents the sensible temperature of air without accounting for the cooling effect of evaporation or the latent moisture content.

Given Data / Assumptions:

• A standard thermometer measures air temperature.
• No water film influences the reading.
• Moderate shielding from radiation and adequate airflow yield accurate readings.

Concept / Approach:
DBT indicates the sensible heat level of air. Moisture affects latent properties and wet-bulb/dew-point temperatures but does not directly affect DBT when measured properly. In contrast, wet-bulb temperature uses a wetted wick and airflow to reflect evaporative cooling; dew-point indicates saturation onset at the current vapour partial pressure.

Step-by-Step Clarification:

Verification / Alternative check:
On the psychrometric chart, vertical lines represent constant DBT. Other properties (wet-bulb, humidity ratio, enthalpy) vary independently across the grid.

Why Other Options Are Wrong:

• (b) Describes wet-bulb measurement.
• (c) Describes dew-point, not DBT.
• (d) Incorrect because option (a) matches the accepted definition.
• (e) Radiation shields are good practice outdoors, but DBT does not require “no airflow.”

Common Pitfalls:
Confusing DBT with operative temperature (which includes radiant effects) or assuming humidity directly alters the DBT reading of a dry thermometer.

Final Answer:
It is not affected by the moisture present in the air