Psychrometrics – identifying the correct term: The temperature indicated by a thermometer at the instant when the moisture present in air first begins to condense is called the dew-point temperature, not the wet-bulb temperature. State whether the given statement (“…is called wet bulb temperature”) is correct or not.

Introduction / Context:In air-conditioning and psychrometrics, three commonly used temperatures are dry-bulb temperature, wet-bulb temperature, and dew-point temperature. The question checks whether you can distinguish between dew-point and wet-bulb properly, because mixing these terms leads to serious design and control errors in HVAC calculations.

Given Data / Assumptions:

• Air–water vapour mixture at near-atmospheric pressure.
• Standard definitions for psychrometric properties.
• Accurate, ventilated thermometers used for wet-bulb measurement with a properly wetted wick.

Concept / Approach:Dew-point temperature is defined as the temperature at which air becomes saturated (relative humidity equals 100%) when cooled at constant moisture content, and condensation begins. Wet-bulb temperature is the equilibrium temperature attained by a wetted wick thermometer due to evaporative cooling into the surrounding airstream. These are different processes and usually yield different temperatures except at saturation.

Step-by-Step Solution:

Verification / Alternative check:On a psychrometric chart, moving horizontally left at constant humidity ratio reaches the saturation curve at T_dp. In contrast, lines of constant T_wb are diagonally sloped; T_wb equals dry-bulb temperature only at 100% relative humidity.

Why Other Options Are Wrong:

• Yes: Incorrect—this confuses dew-point with wet-bulb.
• Only at 100% relative humidity: Even then, the correct name at condensation onset is still “dew-point.” At saturation T_wb equals dry-bulb, but the definition remains distinct.
• Depends on barometric pressure only: Both temperatures depend on moisture content; pressure is not the sole deciding factor.
• Applicable only below 0°C: Dew-point can be above or below 0°C; freezing is not required.

Common Pitfalls:Assuming wet-bulb indicates condensation; assuming dew-point equals wet-bulb at all states; ignoring the constant-humidity-ratio condition for dew-point measurement.

Final Answer:No