Psychrometric processes — dehumidification path On a standard psychrometric chart, which line best represents an ideal dehumidification-at-constant-dry-bulb process (e.g., chemical dehumidification)?

Introduction / Context:
Different dehumidification methods trace different paths on the psychrometric chart. Chemical (adsorption/absorption) dehumidification typically removes moisture at nearly constant dry-bulb temperature, unlike cooling-based dehumidification which lowers dry-bulb too.

Given Data / Assumptions:

• Standard psychrometric chart with x-axis as dry-bulb temperature and y-axis as humidity ratio.
• Idealized chemical dehumidification maintains dry-bulb approximately constant.
• No external heat exchange that would raise or lower T_db significantly.

Concept / Approach:
At constant T_db, removing water vapour reduces humidity ratio while staying on the same vertical line. By contrast, cooling and dehumidifying with a cooling coil generally moves down and to the left toward the saturation curve, not a vertical path.

Step-by-Step Solution:
Identify constant dry-bulb: vertical line on the chart.Remove moisture: move downward (lower humidity ratio).Hence, ideal chemical dehumidification is a vertical downward line.

Verification / Alternative check:
Manufacturer data for desiccant wheels often show near-vertical movement on the chart for the process air path, confirming the idealization.

Why Other Options Are Wrong:
Horizontal line keeps humidity ratio constant (no dehumidification). Inclined and curved lines describe cooling/dehumidifying coils or constant relative humidity paths, not pure chemical dehumidification.

Common Pitfalls:
Assuming all dehumidification implies cooling; method matters. Chemical dehumidification can be nearly isothermal at the process air stream.

Final Answer:
Vertical line (constant dry-bulb temperature, decreasing humidity ratio)