Enthalpy Comparison of Air

Objective

To develop an understanding that air at the same dry bulb temperature can have different enthalpies.

Outcome

Students will realize that energy required to cool a space increases with increase in wet bulb temperature (as cooling requires lowering of enthalpy of ambient condition).

Requirements

Psychrometric chart.

Prerequisites

1. Conceptual knowledge of psychrometry.
2. Understanding of psychrometric chart.

Procedure

Step 1: Plot the following on the psychrometric chart-

1. DB=35 °C, WB=25 °C, RH=45%
2. DB=35 °C, WB=20 °C, RH=25%

Step 2: Ask the following question to students: Which of these ‘air conditions’ have more energy?

Ans: Enthalpy of air at condition (a) (75 kJ/kg) > Enthalpy of air at  the first condition (b) (57 kJ/kg)

Reference image: 

Psychrometric Chart for different air conditions

References

None

Source of Idea