Unit 2.6: Is heat always a dead end, or can it do something useful too?

Sandra Penny, Russell Sage College, and Natalie Bursztyn, University of Montana

Initial Publication Date: September 5, 2024

Summary

Students focus on some thermodynamic aspects of energy: Heat, heat engines, and the second law of thermodynamics. We have already laid the groundwork for these concepts in Unit 2.3 (Energy Types and Transformations), when we noted that some types of energy (sound, wind, thermal energy) indicate that energy is dissipated. Now, it's time for students to look for real-world heat engines. In a jigsaw activity, students analyze data from a variety of real-world heat engines to assess how they are extracting useful energy as heat flows from hot to cold. In a hands-on lab, students build a heat engine boat.

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Learning Objectives

After completing this unit, students will:

  • Use evidence to support claims regarding the nature of heat and its conversion to mechanical energy; interpret patterns in different natural systems.
  • Utilize data to argue how idealized heat engines are related to those that exist in the real world.

Context for Use

We assume that students are comfortable with energy types and transformations and that they have seen energy transformation diagrams like those created in Unit 2.3.

Plan for these materials will take about 150 min of class time to complete, plus an additional 60 min if the Heat Engine Boat Extension lab is also completed.

This unit introduces the Gulf Stream as a Heat Engine. We'll look at the Gulf Stream through a different lens in Unit 3.4: What can we learn by mapping sea surface data? Complete both units to give your students multiple perspective on this important part of our climate system.

Description and Teaching Materials

Teaching Materials:

All slides: Unit 2.6 All Slides v2 (PowerPoint 2007 (.pptx) 122.9MB Aug30 24)

Videos linked in the slides: Silkesslidskivling Final.mp4 (MP4 Video 35.7MB Jul9 24), Pink oyster spore timelapse.mp4 (MP4 Video 33.2MB Jul9 24), undoing entropy.mp4 (MP4 Video 28.1MB Jul9 24), fast undo.mp4 (MP4 Video 2.7MB Jul9 24)

Reflection: Student copy U2.6 Reflection Heat Engines.docx (Microsoft Word 2007 (.docx) 271kB Jul9 24) and Instructor Notes

Sample Student Reflections (this is Reflection 5 & 6): Reflection Examples Redacted.pdf (Acrobat (PDF) 1.8MB Jul8 24)

Heat Engine Jigsaw articles:

Tealight Boat Heat Engine Extension Lab:

  • Materials for each group: About a foot of 1/8" soft copper tubing, empty plastic bottle or other boat-making materials, tea light, tape, scissors, stream tray
  • Student worksheet: U2.6 Heat Engine Boat Lab.docx (Microsoft Word 2007 (.docx) 1.5MB Jul9 24)
  • Instructor notes:

Entropy Demonstration Materials: four clear bottles (ex: 2L soda bottles), two with red-colored warm water, two with blue-colored cold water, a credit card or similar to cap the two bottles. A video of this demonstration is also provided.

Scientist Spotlight Full Resource (In this unit: Eunice Foote): Scientist Spotlight Slides (PowerPoint 2007 (.pptx) 4.6MB Jul8 24)

The Lab(s) is/are assessed as a Science Journal, as always. Science/Lab Journals General Instructions/Rubric (Microsoft Word 2007 (.docx) 2.9MB Aug30 24)

Other Materials: computer and projector, white board or chalk board with markers/chalk.

Pre-Class Assignment(s):

Complete Scientist Spotlight: Eunice Foote. As with all Scientist Spotlights, read a little more on the scientist and be prepared to share something interesting or surprising that you learned about them. Write down a couple of your observations and submit them in the assignment link.

In Class, Part I: Define Heat, Thermal Energy, and Heat Engines (40 min)

  • (5 min): Scientist Spotlight Eunice Foote. She's in this unit because of her pioneering work in understanding how heat functions in our climate system.
  • (10 min): "Reflections on your reflections." Summarize the main points from the class System Maps and clarify any common misconceptions, highlight insightful insights. Use this as a transition to real-world heat engines: What have we observed about heat? Discussion questions:
    • What insights do you have?
      What connections did you make from your system maps?
      What observations (patterns?) have you made about heat?
  • (25 min) Discussion/Lecture: the Gulf Stream is a real-world heat engine. This discussion lays the groundwork to help students interpret the data in the Heat Engine Jigsaw that follows. Students are shown a video of Sea Surface Temperatues in the North Atlantic Ocean for the year 2020 and asked to interpret what they see, eventually iterating to a definition of heat engine that we will use for the upcoming Heat Engine Jigsaw Activity. Important parts of this discussion include:
    • Define the difference between Heat and Thermal Energy (we previously used these words interchangeably)
    • Think-Pair-Share: Use the words Heat and Thermal Energy to describe motions you observed in the Gulf Stream
    • Create an energy transformation diagram for the Gulf Stream (as in Unit 2.3 Energy Transformations Activity)
      • Revisiting a previous skill but in a new context builds vertical alignment in the course and reinforces previous learning (this is "Patterns," a cross-cutting concept).
    • Think-Pair-Share: The Gulf Stream is a "Heat Engine." What evidence is there for this?
    • Make this interesting and relevant to your students: students watch and discuss the trailer for the movie "The Day After Tomorrow," which is based on the idea that global warming has caused the gulf stream heat engine to shut down and nonsensical shenanigans ensue.
      • Your students are interested in climate change, and while the movie is over-the-top, the fact that heat transport through the gulf stream has changed due to global warming is very real and has major climate implications. Your students are currently in a place to really understand why these changes are occurring on a deep level that is usually reserved for upper-level or graduate courses.

In Class, Part II: Heat Engines Jigsaw (45 min)

  • (20 min): Heat Engine Jigsaw Activity, Part 1: Students divide into small groups. Each group reads an article with data from a different real-world heat engine. Each group must explain how the data show evidence of a real-world heat engine as well as make one or two other relevant observations. Guiding Questions:
    • How do the data and/or graphics in your article show something acting as a heat engine? In other words, what evidence do you see that heat is transforming into mechanical energy (i.e., KE or PE)?
    • Heat engines need both hot and cold reservoirs to operate. What evidence is there for a temperature difference? 
    • Draw the energy transformation diagram for your real-world example.
    • Describe one or two other relevant or interesting observations.
    • Be prepared to explain your answers to someone outside your group
  • (25 min): Heat Engine Jigsaw Activity, Part 2: Mix the groups. Everyone finds a new group with no one from their original group. Everyone in the new group explains the heat engine they read about, and then the group answers: 
    • What common observations are there for all the different types of heat engines?
    • What is one individual/unique aspect of each different heat engine that distinguishes it from the rest?

In Class, Part III: DIY Heat Engine Boat Extension Lab (60 min):

  • In this lab exercise, students build a heat engine from copper tubing, a tea light, water, and a boat. As always in this class for lab activities, students complete a Science Journal to document their work (or, use the supplied worksheet if you prefer instead). This tactile, hands-on engineering project requires trial and error and is a nice change of pace from the rest of this unit.
  • Follow-up Discussion questions include:
    • Which SEPs (Science and Engineering Practices) did you apply for this lab? How did you use them to deepen your understanding?
    • How can you use CCCs (and which ones) to relate this lab to real-world phenomena and other class topics?
    • How would you use your lab experimentation to design a guided activity to teach your own students?
    • Why is it important that you experience "trial and error" and "figuring it out" to help you learn with these activities?

In Class, Part IV: Entropy and the Second Law of Thermodynamics (65 min):

  • (20 min) The students have already learned the First Law of Thermodynamics/Law of Conservation of Energy, now it's time to connect their learning about heat and heat engines to entropy and the Second Law of Thermodynamics. Students are initially given a definition of entropy with a few examples, and a deeper understanding is built with the following:
    • Your turn: what are some examples of low entropy and high entropy systems in your life? Remember: Universe always tries to move from less entropy/more order to more entropy/ more disorder.
    • Class demonstration: When hot/red water is placed below cold/blue water, there is an initial temperature and energy imbalance. The hot water and cold water mix to form purple water. The universe has transformed order into disorder via the spontaneous transfer of heat.
      • Note to instructors: this is a great, simple demonstration without expensive materials. The linked video also shows that when hot water is above the cold water, there is no mixing because the water is stably stratified. No reason to demonstrate this now, but in a couple weeks we will be talking about density stratification and layering, so keep this demo handy so you can repeat it or refer to it later.
      • Discussion Questions:
        • Use the words we've been using in this unit to describe what happens when the blue/cold water bottle is placed on top of the red/warm water bottle.
        • Could we force the well-mixed (purple) bottle turn back into the separate hot and cold vessels?
      • Think-Pair-Share questions: 
        • How can you explain the fact that the purple liquid will never spontaneously turn back into the red and blue liquids?
        • What can we say about natural flows of heat?
        • Where is there more "order" vs "disorder" (red/blue/before or purple/after)?
        • Notice any similarities to heat engines? Any differences?
        • Make a statement about the flow of heat and order in the universe.
  • (25 min) Return to Real World Heat Engines Jigsaw: Students return to their original groups to do the following:
    1. Restate how the data are evidence of a real-world heat engine.
    2. Describe how there is evidence of the second law of thermodynamics in your data.
  • (15 min) Wrap up with some thought-provoking and interesting applications: 
    • The second law says that the universe is always moving toward disorder, so how are incredibly organized things (ex: life!) possible?
    • Do Iceman's powers "obey" the 2nd law of thermodynamics?
  • (5 min) Introduce the lesson plan for next time: Lesson Plans are the main summative assignments in this course. Before coming to the next class, students will choose an activity or lab from this unit (waves, energy, power, thermodynamics/heat) that they want to transform into a lesson plan. Give your students a brief overview and point them to the resources that are available to help them create them.
     

Teaching Notes and Tips

The main activity in this unit is a Jigsaw Activity. From the link: "In a jigsaw, the class is divided into several teams, with each team preparing separate but related assignments. When all team members are prepared, the class is re-divided into mixed groups, with one member from each team in each group. Each person in the group teaches the rest of the group what he/she knows, and the group then tackles an assignment together that pulls all of the pieces together to form the full picture, hence the name jigsaw."

The tealight heat engine boat is just one of many simple heat engines that your students can build. Consider giving students options to build whatever kind of heat engine they like instead of just the one you've assigned. This will give them more ownership of the project and make it more of an engineering and design challenge. Here are some other DIY heat engines:


Assessment

Students complete another Scientist Spotlights in this unit. The goal of these is to showcase an array of scientists in fields relevant to the topics of the day, some from long ago and others young and active today, together representing a diversity of people who have all overcome some challenge in pursuit of their scientific passion.

The Extension Lab to build a heat-engine boat is assessed as a Science Journal, as always. A student worksheet is provided as part of the resources the Heat Engine Boat Extension Lab. Instructors can choose to use this worksheet in lieu of the science journal format. If using the science journal format, then powerpoint slides are all that is needed (no worksheet). We will often but not always provide student worksheets. In classes with time constraints, worksheets can be faster, but they do not ask your students to engage as deeply with the practices of science.

In this unit's reflection, students visit some traditional reading materials on the Second Law of Thermodynamics. They'll rephrase what they read and place it in the context of the ways we have described the same law in class. Reflections ask students to put their learning in their own words and also to apply their knowledge in a new and novel situation. Reflections should be about 500 words and they should both discuss content that reflects understanding and thoughtfully reflect on the materials.

References and Resources

This excellent summary discusses applications of heat engines and the second law of thermodynamics to the Earth system to help instructors feel prepared to teach a topic that they might not have thought about much before:

Singh, M. S., & O'Neill, M. E. (2022). The climate system and the second law of thermodynamics. Reviews of Modern Physics, 94(1), 015001.

This is another excellent (and shorter) article about real-world heat engines:

Eschenbach, W. (2013, December 22). The magnificent climate heat engine. Watts Up With That? . https://wattsupwiththat.com/2013/12/21/the-magnificent-climate-heat-engine/

Resources utilized/relevant to the Heat Engine Jigsaw pages: