Psychrometrics — heating with dehumidification During a combined process of heating and dehumidification, how does the dry-bulb temperature of the air change?

Introduction / Context:
Air-handling systems may heat air while also removing moisture (e.g., by desiccant dehumidifiers with a downstream heater). Understanding the direction of property changes is crucial for plotting on the psychrometric chart and sizing coils.

Given Data / Assumptions:

• Simultaneous heat addition and moisture removal.
• No evaporative cooling effects overwhelming the heating.
• Standard atmospheric pressure conditions for the chart.

Concept / Approach:
Heating adds sensible energy to the air, raising its dry-bulb temperature. Dehumidification reduces humidity ratio. On the psychrometric chart, this is typically an inclined path up-and-left or vertical then right depending on process details; in any case, dry-bulb temperature rises when net heating is applied.

Step-by-Step Solution:
Recognize heating → T_db increases.Recognize dehumidification → humidity ratio w decreases.Combine effects: T_db increases while w decreases.

Verification / Alternative check:
Energy balance for moist air: Δh ≈ c_p,ma * ΔT_db + w * Δh_fg + h_vapour changes; with added sensible heat and reduced moisture, ΔT_db is positive.

Why Other Options Are Wrong:
Constant or decreasing dry-bulb contradicts heating; equality with wet-bulb happens only at saturation and is not an outcome of this general process; oscillation is not a defined thermodynamic trend.

Common Pitfalls:
Confusing this with cooling and dehumidification, where T_db falls; or with chemical dehumidification at constant T_db (requires nearly isothermal conditions).

Final Answer:
Increases