Psychrometric chart reading – Specific humidity lines Identify the orientation and spacing of specific humidity (humidity ratio) lines on a standard psychrometric chart.

Introduction / Context:
Reading a psychrometric chart correctly is essential in HVAC design. Each family of lines has a distinct orientation: dry-bulb, wet-bulb, relative humidity, and humidity ratio (specific humidity).

Given Data / Assumptions:

• Standard ASHRAE-style chart axes: x-axis is dry-bulb temperature; y-axis is humidity ratio w (kg/kg dry air).
• Sea-level barometric pressure chart for simplicity.

Concept / Approach:
Specific humidity (humidity ratio w) is plotted on the vertical axis. Therefore, isolines of constant w run horizontally across the chart. Over the typical range, spacing is uniform.

Step-by-Step Solution:
Recall axes: DBT horizontal, w vertical.Lines of constant w are perpendicular to the w axis → horizontal.Chart construction uses uniform w increments → uniform spacing.

Verification / Alternative check:
Compare with other line families: constant RH are curves; wet-bulb are inclined nearly straight lines; DBT are vertical lines. This contrast confirms recognition.

Why Other Options Are Wrong:

• Vertical lines correspond to constant DBT, not constant w.
• Curved/inclined patterns represent RH or wet-bulb families, not w.

Common Pitfalls:
Confusing humidity ratio with relative humidity; assuming non-uniform spacing due to the curved saturation boundary.

Final Answer:
horizontal and uniformly spaced