Exergy At Work

Contents

1. Introduction

2. What Is Exergy?

3. Exergy Equations

4. Exergy Efficiency

5. Are These Metrics Useful?

6. Concluding Remarks

7. Glossary

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Bitesize Edition

• The concept of exergy refers to useful work potential that can be extracted from a system in equilibrium with its environment. It’s a metric worth exploring because energy cannot be created or destroyed, but exergy can when going through an irreversible process of energy conversion. This is often through friction or heat transfer.

• Last week, I discussed energy quality returned vs energy quality invested (EQREI). This metric quantifies energy quality, but typically, energy quality refers to the qualitative concept of high and low-quality energy: with electrical energy being high-quality and low-temperature energy being low-quality energy, for example.

• Energy quality focuses on the ability of a specific form of energy to perform useful work. While energy quality considers the form of energy, exergy focuses on the entire system. So, today I’ll explore the concept of exergy, and later, I will compare it to EQREI.

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Introduction

Today, we’ll explore the concept of exergy, with an X. The concept explores the concept of work, and I believe it is of great usefulness when considering the overall efficiency of our electricity-generating systems. Let’s get exploring.

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What Is Exergy?

Look closely and take note of the “X” in exergy. The concept often refers to available energy or useful work potential that can be extracted from a system in equilibrium with its surroundings.

Since energy with an “N” can’t be created or destroyed, we need some metrics that assess irreversible processes, as we started discussing last week on the topic of energy quality. When we undergo an irreversible process in energy conversion, exergy is destroyed through friction, and heat transfer, for example. In short, exergy can help assess losses in energy conversion processes.

Last week, we looked into energy quality. Let’s refresh what we looked at and compare energy quality and exergy.