Introduction: Peltier Thermo-electric Mini-Fridge: a STEM Classroom Engineering Project

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About: Hello, my name is Ethan Hunt and I’m a STEM teacher, I’m passionate about inspiring the younger generation to learn about technology and become more tech-savvy. I primarily teach 10th graders, but I also have …

My name is Ethan Hunt and I am a STEM teacher in Dallas, Texas, teaching students from grades 9 to 11. I'm excited to share with you my latest classroom project - a small mini-fridge that I designed to teach electronics to my students in a fun and engaging way. This prototype, which can store up to three cans, is a demonstration tool that I made in order to use for my classroom. I built this prototype at home, whilst having no access to the laser cutters at school, but I'm eager to see how my students will utilize these tools to create their own, better versions.

This mini-fridge is capable of lowering the temperature inside to about 11 C (51.8 F), making it perfect for keeping my cans nice and cool whilst working. It's also whisper quiet, operating at just 30 decibels when you're within sixteen feet of it. My goal is to challenge my students to create a mini-fridge that is energy-efficient and capable of lowering the interior temperature as much as possible - preferably to about 5 C (41 F). This course involves 13 Lessons each 50 minutes long. Feel free to shorten or lengthen those lessons as per your needs. I recommend that groups of 3-5 students work together on this project for it to be more cost-efficient and interesting for everyone getting involved. It would be ideal to allow the students more time for them to create several fusion 360 prototypes and test various insulating materials in their product. Overall I hope this course is helpful to any teachers out there who want to offer their students a fun and enjoyable learning course for their students. I especially like how this course offers several lessons which implement activities all leading up to the students designing a final product by themselves.

Supplies

Materials:

  • Insulation sheets of any material (1 inch thickness, about 400mm*400mm per group)

(Let the students decide which insulating material they would like to choose, I personally went with polystyrene as I had some left over packaging and was able to upcycle the polystyrene)

  • Acrylic or MDF (3 mm or thicker preferably, about 1000mm*1000mm)

(I used carboard as this was a demonstration piece which needed to show its functionality however for my class I will allow them to use the laser cutter for acrylic to make a final product)

Tools:

  • Pen, ruler, scissors, pliers, utility knife, Phillips head screw driver, UHU glue, clear tape, wire stripper
  • Soldering iron, resin flux core solder, tweezers, brass cleaning sponge, normal wet sponge
  • Hot glue gun, hot glue sticks, UHU glue
  • Solder drip mat, Safety glasses
  • Autodesk Fusion 360 software for laser cutter and CNC

Machinery:

  • Laser cutter (For acrylic, MDF sheets, and insulation sheets)
  • Drill (For the holes in the acrylic/MDF/insulation sheets)
  • Heat gun (For heat shrink)
  • Computers with Fusion 360 installed and Excel or google sheets available.

Please do note that for the individual lessons you will need to look at the materials list of each lesson rather than here! The materials listed here are only for the main product.

Step 1: Understanding Peltier Thermo-Electric Modules

Lesson 1: Explaining the Peltier effect and how the module works to the students.

Lesson Objective: Students will learn about Peltier modules and how they can be used for cooling, heating, or creating a potential difference.

Materials needed:

  • Peltier Cooling system kit fully assembled (With the fan on the small radiator removed)
  • Multimeter
  • Ice pack
  • Heat pack
  • Computers for students
  • DC power supply (any supply with adjustable voltages and amperes)

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of Peltier modules and how they can be used for cooling or heating. Show students a Peltier module and explain how it works along with the youtube video provided.
  • Demonstration 1 (15 minutes): Demonstrate how a Peltier module works. Plug the Peltier module along with the fan into the DC power supply. Set the power supply to 12 volts at 6 amps and ensure the fan blows into the heatsink rather than out of it. Once on, allow the Peltier module to operate for at least a minute. After that you may allow the students to touch the small heatsink on the Peltier module but not for more than a couple seconds otherwise ice burns can occur! Or simply see some light ice build up on the heatsink after a few minutes.
  • Demonstration 2 (15 minutes): Demonstrate how to create a potential difference using a Peltier module, an ice pack, and a hand warmer pack. Link up the Peltier to the multimeter and activate the ice pack, place the pack on the table with the Peltier module resting on top of it. Then activate the heat pack and place that on top of the Peltier module carefully ensuring it doesn't touch the icepack. Once done, the multimeter should be reading very low voltages coming from the Peltier module.
  • Class Discussion (10 minutes): Discuss the results of the demonstration and how Peltier modules can be used for cooling or heating. Ask students to brainstorm other applications for Peltier modules.
  • Homework (30 minutes): For homework, students will write a short essay on the applications of Peltier modules and how the modules work. They should include at least three different applications of the modules and explain how Peltier modules are utilized in each application.

Resources:

Step 2: Learning About Various Insulating Materials

Lesson 2: Finding differences in performance between different types of insulation sheets

Lesson Objective: Students will learn about the role of thermal insulation materials in reducing heat transfer by conduction, convection, and radiation, as well as the design and implementation of insulating materials in construction and engineering.

Materials needed:

  • Expanded polystyrene sheet (EPS)
  • Extruded polystyrene sheet (XPS)
  • Polyisocyanurate (Polyiso, ISO)
  • Thermometer
  • Kettle with water
  • Stopwatch
  • Ruler
  • Notebook and pen
  • 1lb weight

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of thermal insulation and its importance in reducing heat transfer. Explain the three modes of heat transfer (conduction, convection, and radiation) and how insulation materials can reduce each mode of heat transfer. Show students examples of different types of insulation materials and their applications in construction and engineering.
  • Activity (20 minutes): (Please supervise students when using boiling water)
  1. Boil water in a kettle and pour it into a beaker.
  2. Place the thermometer in the beaker and record the temperature of the water.
  3. Cover the beaker with the insulation sheet and place the weight on top.
  4. Record the temperature of the water every 30 seconds for 5 minutes.
  5. Repeat steps 3-4 for each insulating sheet.
  6. Calculate the average temperature for each insulating material over the 5-minute period.
  7. Record the results in a notebook.
  • Class Discussion (15 minutes): Discuss the results of the experiment with your students. Ask them to compare the effectiveness of each insulating material in reducing heat transfer. Encourage them to think about how these materials can be used in real-world applications, such as in construction and engineering. Go over the link below with the students.
  • Group Discussion (5 minutes): Allow the groups to choose one insulating material for their minifridge based on what they have learnt in the lesson.

Resources:

Step 3: The Science Behind Cold Air Sinking and Heat Dissipation

Lesson 3: The Science Behind Cold Air Sinking And Heat Dissipation

Lesson Objective: Students will learn about the science behind cold air sinking and heat dissipation, including the role of convection currents in the atmosphere.

Materials needed:

  • None

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of cold air sinking and heat dissipation. Explain how the density of air changes with temperature and how this affects the movement of air in the atmosphere. Show students examples of convection currents in the atmosphere and how they contribute to weather patterns.
  • Learning Session (20 minutes): Discuss the science behind cold air sinking and heat dissipation in more detail. Explain how the movement of air in the atmosphere is driven by differences in temperature and pressure. Discuss how convection currents form and how they contribute to weather patterns. Show students examples of convection currents in the atmosphere and how they can be observed using satellite imagery.
  • Class Discussion (10 minutes): Discuss the importance of understanding the science behind cold air sinking and heat dissipation, including its impact on weather patterns and climate change. Ask students to brainstorm ways in which they can contribute to reducing the impact of climate change.
  • Group Discussion (10 minutes): Allow the groups to think of how they can use the knowledge gained in this lesson to their advantage. This could be simple ideas like having the mini-fridge lid on top to lose less cold air when opening it or ensuring there is enough surface area for the heat to dissipate on the hot side. Let the students think about ways to make the fridge more energy efficient and how they can use their knowledge to make it as environmentally friendly as possible whether it is upcycling old insulation material or using thinner but better insulation.

Resources:

Step 4: Designing a Prototype Using 2D Sketches

Lesson 4: Sketching ideas

Lesson Objective: Students will learn how to design a prototype using 2D sketches.

Materials needed:

  • Pencils
  • Paper
  • Ruler
  • Eraser

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of designing a prototype using 2D sketches. Explain how 2D sketches can be used to visualize an idea before creating a 3D model. Show students examples of different types of prototypes and their applications in todays world of product design.
  • Learning Session (15 minutes): Discuss the process of designing a prototype using 2D sketches. Explain how to create a rough sketch of the prototype using pencils and paper. Encourage students to experiment with different shapes and sizes to refine their design. Show students how to use a ruler to create straight lines and accurate measurements on their grid paper.
  • Group Task (25 minutes/homework): Ask students in their groups to start generating ideas for their mini-fridge based on all of the information they have learnt so far. Allow them to take the task further by finishing the sketches if needed for homework. Sketches should be supported by writing to explain what each part of the sketch does.

Resources:

Step 5: Utilizing 3D Software to Design the Final Product

Lesson 5,6,7 : Using Fusion 360 to make a 3D model (Allow up to 4 lessons if necessary)

Lesson Objective: Students will learn how to use Fusion 360, a 3D modeling software, to design the final product.

Materials needed:

  • Computers with Fusion 360 installed
  • All the parts for the mini-fridges (for measuring sizes)

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of 3D modeling and its importance in product design. Explain to the students how 3D modeling software can be used to create detailed virtual prototypes and test their functionality and performance before moving on to physical production. Show students examples of different types of products that have been designed using 3D software such as fusion 360 or tinker cad.
  • Discussion (10 minutes): Discuss the importance of utilizing 3D software to design the final product, including its impact on the final product design. Ask students to brainstorm other applications of 3D modeling software in product design.
  • Learning Session (30 minutes): Discuss the process of designing a product using Fusion 360. Explain how to create a 3D model of the product using the software. Encourage students to experiment with different shapes and sizes to refine their design. Show students how to use the various tools available in Fusion 360 to create a detailed 3D model of the product.
  • Group task (1 hour 40 minutes): Allow students to design their final product in fusion 360. Please note that it may take up to 2 lessons to create an accurate design. Ensure students create their model in fusion to scale with sizes that match the components that they will be putting in such as the Peltier modules and the power supplies.

Resources:

Youtube tutorials if students need help in fusion 360:

Step 6: Using the Laser Cutter

Lesson 8,9: Understanding how to use the laser cutter and then using it to cut out the fusion designs

Lesson Objective: Students will learn how to use a laser cutter and how to export files from Fusion 360 to DXF.

Materials needed:

  • Computers with Fusion 360 and laser cutter software installed
  • Laser cutter
  • Materials to cut (e.g., MDF, Acrylic)

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of laser cutting and its importance in product design. Explain how laser cutting can be used to create precise cuts and engravings on a variety of materials in the industry. Show students examples of different types of products that have been created using laser cutting. Show the students the resources provided on laser cutting acrylic, MDF, and insulation sheets.
  • Discussion (10 minutes): Discuss the importance of using a laser cutter in product design, including its impact on the final product design. Ask students to brainstorm other applications of laser cutting in product design.
  • Learning Session (30 minutes): Discuss the process of using a laser cutter. Explain how to prepare a file for laser cutting using the Fusion 360 software. Show students how to export a file from Fusion 360 to DXF format. Demonstrate how to import the DXF file into the laser cutter software and set up the laser cutter for cutting. Also explain the necessary safety precautions that need to be taken when using a laser cutter.
  • Activity (20 minutes): Allow students to prepare their files and export them into the laser cutter software.
  • Activity (30 minutes): Allow students to laser cut their files. Make sure to guide the students through the process and check the settings the laser cutter needs to be set to depending on material chosen.

Resources:

Note: I was not able to laser cut at home so I used a utility knife to cut polystyrene with a ruler. However I highly recommend laser cutting the insulation sheets as it will be much more precise and easier.

Step 7: Soldering Electronics

Lesson 10: Soldering the Peltier modules and connecting the power supply

Lesson Objective: Students will learn how to solder wires together and maintain electrical safety while doing so.

Materials needed:

  • Soldering iron
  • Solder drip mat
  • Solder
  • Pliers
  • Wire strippers
  • Wires
  • Heat-shrink tubing
  • Safety Glasses
  • Tweezers
  • Peltier modules
  • Latching power button
  • Male inlet socket
  • Power supply
  • Phillips head screw driver

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of soldering and its importance in electronics. Explain how soldering can be used to create a permanent connection between electronic components. Show students examples of different types of electronic circuits and their applications.
  • Learning Session (10 minutes): Discuss the process of soldering wires together. Explain how to prepare the wires for soldering and how to use the soldering iron to create a connection. Demonstrate how to solder wires together using helping hands and heat-shrink tubing. Show students how to use pliers to prepare the wires for soldering.
  • Activity (30 minutes): Allow students to Solder their Peltier modules to the latching power button. Then they must solder wires to the male inlet sockets. Once done, the students should be left with 2 Peltier modules and all the fans soldered together (combining 3 wires from each polarity on each module to one wire as seen in the pictures above) which is connected to the latching button.

Safety Tips:

  • Wear Safety glasses and lay the solder drip mat before starting.
  • Perform soldering in a well-ventilated area.
  • Never touch the tip of the soldering iron.
  • Turn off and unplug the soldering iron when finished using.
  • Hold the wires using clamps or tweezers.

Resources:

Step 8: Final Assembly

Lesson 11: Assembling the Mini-fridges:

Lesson Objective: Students will learn how to work together as a team to assemble their mini-fridge with all the electronics as quickly and as efficiently as possible.

Materials needed:

  • Mini fridge components
  • Screwdriver
  • Screws
  • Insulation sheets and acrylic/MDF sheets
  • Hot glue or UHU glue
  • Magnets

Lesson Plan (Allow 1 whole lesson for students to fully assemble their mini-fridges):

  • Gluing the insulation together: Students should use either hot glue or UHU glue to stick the insulating sheets together and clamp them for a few minutes for the glue to bond.
  • Attaching the magnets to the foam and acrylic/MDF: Magnets can be easily pressed into the insulation and hot glued to it. Students can choose if they want magnets attached to the acrylic/MDF doors or have screws which attach to the magnets.
  • Drilling holes into the acrylic/MDF if necessary: Allow students to drill holes into the acrylic if their laser cut file didn't already include precut holes.
  • Screwing together the acrylic/MDF and gluing it to the insulation: Then Students should use the screws to screw the acrylic/MDF to the insulation or to other pieces of acrylic/MDF using a Phillips screw driver. Before screwing in fully, students should apply a small amount of glue in between the layers for a better bond. Since insulation isn't solid, it is recommended after screwing to fill the gaps with hot glue for a more secure and tight model. The hinges can then also be attached to the doors with screws and hot glue.
  • Lining the inside of the fridge with aluminum foil tape: Once the fridge is fully assembled in its parts, students are highly recommended to use the aluminum foil tape to line the interior of the fridge for better conduction inside. I personally lined the top of the fridge outside as well for less heat absorption in the summer and better heat dissipation but it isn't necessary.
  • Sticking the draft seal strip: The draft seal strip should ideally be cut at 45 degree angles so that it can be stuck at 90 degree angles in the fridge. The draft seal strip is only needed to make sure the door is sealed airtight. My fridge however has the top removable so i placed a seal strip there.
  • Attaching the dust filter to the Peltier module fans: The dust filter is to be cut to size of the fans and screwed into the fan holes. It will protect the fans from small debris and any wires.
  • Screwing the electronics into the fridge: Finally the electronics can be placed into the fridge and screwed into place using the normal screws or the screws that come with the components.
  • Screwing the wires from the Peltier modules and socket into the power supply: The wires from the socket has to be screwed into the power supply now that it is attached and the wires from the latching power button screwed into the power supply output.
  • Hot gluing all the small gaps for an airtight seal: This is an optional step but will help with making the fridge as rigid and airtight as possible. Students can hot glue any tiny gaps inside the fridge or outside to ensure the materials are flush and won't let cold air escape from inside.

Step 9: Testing the Fridge and Gathering Temperature Data

Lesson 12: Testing and recording

Lesson Objective: Students will learn how to test products , gather data, and plot data.

Materials needed:

  • Thermometer (I didn't have one on hand so I used an Arduino with a DH11 module which does the job just as well, however please note that the DH11 module is not capable of recording subzero temperatures)
  • Pen and paper
  • Soda cans
  • Computers

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of testing and gathering temperature data and its importance in product design. Explain how data can be used to optimize the performance of the product and learn from the data. Show students examples of different types of products that have been optimized using testing data and how the tests have been done.
  • Learning Session (10 minutes): Discuss the process of testing and gathering temperature data. Explain how to use a thermometer to measure temperature and how to draw a data table to graph the data later on. Explain also how to draw a line graph with temperature on the Y-axis and time on the X-axis in google spreadsheets or excel.
  • Activity (30 minutes): Allow students to start gathering and recording temperature data. Encourage them to use the skills they have learned to create unique temperatures data sets. Also allow students to test the internal temperature of the mini-fridge under different circumstances, such as when empty, or when fully loaded with cans. Students can also test the temperature of the liquids themselves after several minutes. For better results I recommend giving the students one full lesson for only testing because soda cans take a while to cool down.
  • Optional Homework: Feel free to allow students to take their mini-fridges home and test them whilst creating graphs and plotting data. Please note that testing mini-fridges over a longer span of time gives better results and more comparable data to real life situations.

Resources:

Step 10: Improving a Product

Lesson 13: Improving a Product with Testing Data

Learning Objective: Students will learn how to analyze and improve a product using testing data.

Materials needed:

  • Product prototype
  • Testing data
  • Computer
  • Graphing software

Lesson Plan:

  • Introduction (10 minutes): Introduce the concept of analyzing and improving a product using testing data. Explain how testing data can be used to optimize the performance of a product. Show students examples of different types of products that have been optimized using testing data.
  • Learning Session (20 minutes): Discuss the process of analyzing and improving a product using testing data. Explain how to use testing data to identify areas for improvement in their product. Demonstrate how to use graphs the students plotted to analyze testing data. Explain to students the various ways that data can be plotted and how they differ, e.g. line graphs vs bar graphs.
  • Group/Class Discussions (30 minutes): Allow students to analyze their own product using testing data. Encourage them to use the skills they have learned to create unique and innovative ways to improve their product as well as coming up with ideas for improving other groups' products. Students should feel free to look at other students' products and determine flaws as well as discuss ways in which other groups have done certain things better such as using higher density insulation or more insulation being used.

Resources:

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