On a standard psychrometric chart, which family of lines represents constant dry-bulb temperature (DBT)?

Introduction / Context:
The psychrometric chart is a graphical map of moist-air properties. Correctly identifying the DBT lines is fundamental for plotting air-conditioning processes such as sensible heating/cooling and mixing.

Given Data / Assumptions:

• Standard atmospheric-pressure psychrometric chart.
• Axes: DBT (°C) on the abscissa and humidity ratio (kg/kg dry air) on the ordinate.
• Other properties drawn as families of lines.

Concept / Approach:
By convention, the dry-bulb temperature increases to the right on the horizontal axis. Therefore, constant DBT is represented by vertical lines. Because DBT scale is linear, these vertical lines are uniformly spaced.

Step-by-Step Solution:
Locate the horizontal axis labeled in °C (DBT).Observe that moving right increases DBT; staying at a constant DBT implies a vertical movement.Hence, constant DBT lines are vertical and, due to linear scaling, are evenly spaced.

Verification / Alternative check:
Plot a simple sensible cooling process (no moisture change): it travels horizontally left along a line of fixed humidity ratio, crossing several vertical constant-DBT lines.

Why Other Options Are Wrong:

• Horizontal lines: represent constant humidity ratio.
• Curved lines: correspond to constant relative humidity.
• Inclined lines: typically represent constant wet-bulb temperature/enthalpy.

Common Pitfalls:
Confusing constant enthalpy (inclined) with constant DBT; forgetting that DBT is the x-axis variable.

Final Answer:
Vertical and uniformly spaced lines