Reading the psychrometric chart: The horizontal, non-uniformly spaced lines on a standard psychrometric chart correspond to which property?

Difficulty: Medium

Correct Answer: Dew-point temperature

Explanation:


Introduction / Context:
Being fluent with psychrometric charts is essential in HVAC. Different families of lines represent different properties; recognizing their orientation and spacing avoids reading errors.



Given Data / Assumptions:

  • Standard ASHRAE-style chart orientation.
  • Pressure approximately 1 atm.
  • Chart axes: humidity ratio (vertical) vs. dry-bulb temperature (horizontal).


Concept / Approach:
On typical charts: dry-bulb are vertical straight lines; humidity ratio lines are horizontal and generally uniformly spaced; wet-bulb are diagonally sloped lines; relative humidity are curved lines; dew-point temperature corresponds to horizontal projection to the saturation curve and is shown as horizontal, non-uniformly spaced markings along saturation.



Step-by-Step Solution:

Identify horizontal families: both humidity ratio and dew-point relate to horizontal moves.Humidity ratio lines are typically uniformly spaced grid lines.Dew-point scales along the saturation curve appear as horizontal references that are non-uniformly spaced due to non-linear saturation properties.Therefore, the description “horizontal and non-uniformly spaced” best matches dew-point temperature scales.


Verification / Alternative check:
Cross-check with a standard chart legend; RH lines are curved, DBT vertical, WBT sloped, w horizontal, and T_dp indicated along saturation with non-uniform spacing.



Why Other Options Are Wrong:
Dry-bulb are vertical; wet-bulb are slanted; specific humidity lines are horizontal but typically near-uniform in spacing; RH are curved.



Common Pitfalls:
Confusing humidity ratio horizontal lines with dew-point markings; remember dew-point is read at the saturation boundary.



Final Answer:
Dew-point temperature

More Questions from Heat Transfer, Refrigeration and Air Conditioning

Discussion & Comments

No comments yet. Be the first to comment!
Join Discussion