Understanding Exergy Transfer — Lesson 3

This lesson covers the concept of exergy and its transfer in a system due to its interaction with the surroundings. It explains how exergy can be added or removed from a system as a result of work, heat, and mass interactions. The lesson further elaborates on how the exergy of a system changes when work is done by the system, and how it increases when work is done on the system. It also discusses the impact of adding or removing mass on the exergy of a system. The lesson provides a detailed explanation of how heat interaction affects exergy transfer, and how the direction of heat flow and exergy flow can be opposite depending on the system's temperature relative to the ambient temperature. The lesson concludes with the derivation of an expression for exergy change in a system as a result of both heat and work interactions.

Video Highlights

02:17 - Detailed analysis of heat interaction and its influence on exergy transfer
04:02 - Different states of a system and their impact on exergy
09:55 - Explanation of the concept of exergy transfer and destruction
11:48 - Concept of Second Law efficiency for different types of devices
13:57 - Application of the concepts of exergy and Second Law efficiency in practical examples

Key Takeaways

- Exergy can be transferred, added to, or removed from a system due to its interaction with the surroundings.
- The interactions with the surroundings may be classified as the addition or removal of work, heat, and mass.
- The direction of heat flow and exergy flow can be opposite to each other depending on the system's temperature relative to the ambient temperature.
- The concept of second law efficiency provides a more general and insightful performance metric for any device as it takes into account the entropy generated in the universe due to internal and external irreversibilities.