Reading the psychrometric chart: The family of curved lines sweeping from the saturation curve across the chart represent which psychrometric property?

Introduction / Context:
Interpreting a psychrometric chart quickly is vital in HVAC design and troubleshooting. Each set of lines corresponds to a specific property of moist air.

Given Data / Assumptions:

• Standard chart with dry-bulb temperature on the horizontal axis and humidity ratio on the vertical axis.
• Saturation curve forms the 100% relative humidity boundary.

Concept / Approach:
On a typical chart: vertical lines are constant humidity ratio; horizontal lines are constant dry-bulb temperature; lines slanted downward to the right are constant wet-bulb temperature; and the smoothly curved family of lines running from the saturation curve toward the dry region are constant relative humidity (RH) lines.

Step-by-Step Solution:

Verification / Alternative check:
Cross-referencing the chart legend confirms the property families and their geometric orientation, including constant wet-bulb lines being nearly straight and slanted, not smoothly curved like RH lines.

Why Other Options Are Wrong:

• Dry-bulb temperature: Shown as horizontal straight lines.
• Wet-bulb temperature: Generally straight or slightly curved slanted lines, not the family in question.
• Dew point temperature: Read horizontally from saturation; not a family of curved lines across the field.

Common Pitfalls:
Confusing wet-bulb lines with RH lines; always check line labels and orientation.

Final Answer:
Relative humidity