Definition check — dew-point temperature of moist air State whether the following is correct: “Dew-point temperature corresponds to the saturation temperature of the water vapor at its partial pressure in the air mixture.”

Introduction / Context:Dew-point temperature (T_dp) is the cornerstone of condensation control in HVAC and process drying. It sets the temperature to which air must be cooled at constant pressure for saturation to begin.

Given Data / Assumptions:

• Moist air behaves as an ideal mixture of dry air and water vapor.
• Total pressure is approximately constant for the state considered.

Concept / Approach:The water vapor in moist air exerts a partial pressure p_v. The dew-point temperature is defined such that the saturation pressure of water at T_dp equals p_v. This is exactly the statement that “dew point corresponds to the saturation temperature at the vapor’s partial pressure.”

Step-by-Step Solution:Measure or compute p_v from RH and T_db.Find T such that p_sat(T) = p_v.This T is the dew-point temperature.At T_dp, further cooling causes condensation at constant pressure.

Verification / Alternative check:Using charts or steam tables, matching p_v to p_sat(T) produces the same dew-point as read directly from a psychrometric chart, confirming the equivalence.

Why Other Options Are Wrong:(b) contradicts the standard definition. (c) Altitude changes total pressure but the definition via partial pressure still holds. (d) Dew-point is defined for any RH; at RH = 100% the dew-point equals the current dry-bulb. (e) Dew-point is a state property independent of the specific cooling path.

Common Pitfalls:Confusing dew-point with wet-bulb; wet-bulb depends on evaporative cooling and heat–mass transfer, not just p_v.

Final Answer:True