Entropy and Power Generation

Activity Overview: The second law of thermodynamics states that the entropy of an isolated system always increases as energy is converted. Moving from fuel (high order) to heat or smoke (low order) is a natural process of entropy. Pollution with the highest disorder or highest entropy is the hardest to clean up. For example, because air pollution is made up of very small, highly dispersed particles, it is difficult to clean up. Water pollution can flow with the water, so water pollution falls between air pollution and solid pollution. Solid pollution is the most ordered because it does not flow or disperse without help from air and water.

Problem Statement:

Explain every day examples of entropy and identify the entropy level of different byproducts of electricity production.

For this activity, individuals or groups can evaluate different types of electric power plants. Here is a list of examples:

• coal-fired combustion
• integrated gasification combined cycle
• thermonuclear

Students should investigate the byproducts of each process and then assess whether the byproduct has a high, medium, or low level of entropy before also evaluating based on definition how difficult the byproduct is to manage.

For example, spent uranium fuel is the byproduct of thermonuclear reactors. The fuel is a solid, with relatively low entropy. Spent uranium can be repackaged and shipped via trucks for long-term storage. It can be reprocessed into more fuel, as is done in France.

Alternatively, coal combustion produces a variety of different byproducts including coal ash, sulfur oxides, nitrogen oxides, carbon monoxide, carbon dioxide, and other particulates. Solid particles have a lower entropy level than gasses, and larger solid particles, such as ash, at at the lowest entropy level and the easiest to manage. Gases with their high entropy level require larger investments of time, materials, and money to manage. One example of managing carbon dioxide emissions is trapping, pressurizing, and storing the gas in large subterranean caverns.

Assessment Criteria:

Students should be able to identify different byproducts of electricity production based on their knowledge of energy resources and their own research. Students will identify the state of matter of the different byproduct and use that as an indicator of the relative entropic level of different byproducts from the same source. Based on the assumption that higher entropic level correlates with more difficult management, students will assess the relative difficulty of managing the byproducts. Information from the Internet, publications, and other resources can strengthen this assessment.

The students' analysis should be anchored in a real example of electricity production, and it should demonstrate a thorough understanding of the underlying law of thermodynamics.

Resources:

Chapter 28: Energy and the Environment from Energy 101: Energy Technology & Policy provides an introduction to different cross-sectoral environmental issues related to the energy sector. The final section examines how entropy relates to different wastes. Access to Energy 101 for Texas students and teachers is provided for free by the State Energy Conservation Office as part of the Watt Watchers of Texas program.

TEKS

PHYS.6E

Portions of this activity have been reprinted from Chapter 28: Energy and the Environment from Energy 101: Energy Technology & Policy

Watt Watchers of Texas is a Partner Program of Smart Energy Education.