Psychrometrics — sensible heating During a purely sensible heating process of air (no moisture added or removed), what happens to the dry-bulb temperature?

Introduction / Context:Sensible heating is a foundational psychrometric process used in space heating and air-handling units. Understanding how state points move on the chart helps with coil selection and energy calculations.

Given Data / Assumptions:

• No moisture is added or removed (humidity ratio remains constant).
• Air is treated as an ideal gas–vapour mixture at low to moderate pressures.
• Process is “sensible” only: enthalpy rise is due to temperature increase of the moist air.

Concept / Approach:On a psychrometric chart, constant humidity ratio corresponds to a horizontal line. Sensible heating shifts the state point horizontally to the right, increasing dry-bulb temperature while keeping specific humidity unchanged.

Step-by-Step Solution:Identify variables: dry-bulb temperature T_db, humidity ratio w.For sensible heating: Δw = 0 and ΔT_db > 0.Therefore, T_db must increase.

Verification / Alternative check:Energy balance for a control volume: Q̇_sensible = m_dot * c_p,ma * (T_out − T_in), with c_p,ma approximately constant, giving a direct proportionality between heat added and increase in T_db.

Why Other Options Are Wrong:Constant or decreasing T_db contradicts the definition of sensible heating. The dry-bulb does not automatically equal wet-bulb except at saturation, which is not implied here.

Common Pitfalls:Confusing “sensible heating” with “reheating after dehumidification,” where humidity changes first and then T_db is raised; here we specify no moisture change throughout.

Final Answer:Increases