Question

Process of cooling or heating of air without changing the humidity ratio is represented on a psychrometric chart by

• A. Vertical line
• B. Horizontal line
• C. Curved line
• D. Inclined line

Hint:

To remember psychrometric processes:
- Horizontal line \(\rightarrow\) Sensible heating/cooling (Constant humidity ratio, \(W = \text{constant}\)).
- Vertical line \(\rightarrow\) Humidification/Dehumidification (Constant dry-bulb temperature, \(T_{db} = \text{constant}\)).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Psychrometrics is the study of the physical and thermodynamic properties of moist air (mixtures of dry air and water vapour).
These properties are represented graphically on a psychrometric chart, which is used to analyze air conditioning, drying, and ventilation processes.

Step 2: Detailed Explanation:
Let us look at how the key variables are plotted on a standard psychrometric chart:
- Dry-Bulb Temperature (\(T_{db}\)): Plotted on the horizontal axis (x-axis), with values increasing from left to right.
- Humidity Ratio (\(W\)): Also known as moisture content, this is the mass of water vapour per unit mass of dry air. It is plotted on the vertical axis (y-axis), with values increasing from bottom to top.
- Constant Humidity Ratio Lines: Since the humidity ratio is on the vertical axis, lines of constant humidity ratio run horizontally across the chart.
- Sensible Heating and Cooling:
When air is heated or cooled without adding or removing moisture (known as sensible heating or cooling), the humidity ratio (\(W\)) remains constant.
Since \(W\) does not change, the process must follow a line of constant humidity ratio, which is represented by a horizontal line on the psychrometric chart:
- Moving to the right along this line represents sensible heating.
- Moving to the left along this line represents sensible cooling.

Step 3: Final Answer:
The correct option is (B).