Hands-on Activity Cleaning Air with Balloons

Learning Objectives

After this activity, students should be able to:

• Describe and explain how an electrostatic precipitator works as a pollutant recovery method.
• Describe how engineers create technology to help industry clean up their air pollution.
• Apply knowledge of percentages to understand technological efficiency.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

Materials List

For the student activity, each student needs:

• ½ teaspoon ground black pepper (or small bits of paper)
• 1 balloon
• 1 sheet of white paper

For the class demonstration:

• Ground black pepper
• 1 piece of plastic (PVC) tubing, 3-5 ft. long, 2.5 in. diameter
• 1 plastic shopping bag
• 1 sheet of white paper

Worksheets and Attachments

Introduction/Motivation

Industry is a large contributor to air pollution. Environmental and mechanical engineers create new techniques to prevent industrial air pollution. The type of technology we are going to examine today is the electrostatic precipitator. An electrostatic precipitator uses static charges to clean pollutants out of the air. Can you give an example of static electricity? Have you ever had a sock stick to your shirt or pants when it came out of the dryer?

In an electrostatic precipitator, a static charge makes the pollution particles stick to electrified plates of metal. Refer to Figure 1 or the attached How an Electrostatic Precipitator Cleans Polluted Air Diagram. This is similar to how static electricity in clothing attracts small bits of dust and lint. Then, the collected dirt is knocked loose, collected and removed. Electrostatic precipitators are 99.9% efficient. They are often used, instead of other technologies, in situations in which the particles are suspended in very hot gases, such as in emissions from power plants, steel or paper mills, smelters and cement plants.

Can you picture how this works? Today, we are going to model electrostatic precipitator technology in class.

Procedure

Before the Activity

Student Activity

1. Ask the students: What is static electricity? Explain and give an example (e.g., clothes sticking together in the dryer). Ask students to brainstorm ways static electricity can be used to clean air pollution.
2. Give each student a balloon and some black pepper on a sheet of paper.
3. Ask the students to blow up their balloons and rub them on their hair or a piece of cloth.
4. Hold the balloon over the pepper on the paper. What happens to the pepper? See Figure 2.

Class Demonstration

1. Ask the students to record their observations of the class demonstration. Instruct them to record anything that seems important.
2. Pull the plastic grocery bag through the PVC tube so that the inside edge of it becomes charged with static electricity.
3. Gently pour some pepper through the tube while holding it over a piece of white paper. Some pepper should stick to the inside of the tube (in the same way that it was attracted to the balloon).
4. Discuss student observations. Explain that electrostatic precipitators capture small particles (called particulate matter) from the polluted air before the air is released into the atmosphere. Describe the purposes for which we use an electrostatic precipitator.
5. In conclusion, ask the students the following questions and discuss as a class:

• Does the electrostatic precipitator remove all of the particulates? (Answer: No, not all of them. Electrostatic precipitators are about 99.9% efficient.)
• How does this compare to the efficiency of a wet scrubber? Which one is better? (Answer: A wet scrubber is 95% efficient, so precipitators are more efficient).
• If the precipitators are more efficient, why would you ever want to use a wet scrubber? (Answer: Wet scrubbers work better on gases.)

Assessment

Pre-Activity Assessment

Discussion and Brainstorming: As a class, have the students engage in open discussion. Remind students that in brainstorming, no idea or suggestion is "silly." All ideas should be respectfully heard. Take an uncritical position, encourage wild ideas and discourage criticism of ideas. Have them raise their hands to respond. Write their ideas on the board. Ask the students:

• What is static electricity? (Explain and give an example, e.g., clothes sticking together in the dryer.)
• How might static electricity be used to clean air pollution? (This will be shown in the student activity and class demonstration.)

Activity Embedded Assessment

Observations: Ask students to pay close attention and record their observations of the class demonstration, explaining to them that this is what real scientists and engineers do. Instruct them to record anything that seems important.

Post-Activity Assessment

Observations: Discuss student observations.

Drawing/Journaling: Depending on the students' age, have them draw a picture or write in their own words a description of how an electrostatic precipitator works to clean polluted air. Ask for volunteers to share their descriptions with the class.

Safety Issues

• Keep the pepper away from your eyes!

Troubleshooting Tips

• A 2.5 inch diameter PVC pipe is wide enough for students to see the pepper inside the tube.
• While the pepper usually only sticks to the top end of the tube, it still demonstrates the concept effectively.

Activity Extensions

Find local examples of electrostatic precipitators and arrange a field trip. What pollutants does their electrostatic precipitator remove? What do they do with the particulates collected?

Much smaller than industrial electrostatic precipitators, electrostatic air cleaners designed for the home use an electrostatic force to move air molecules and trap small airborne particles (0.05 – 30 microns in size, such as pet dander or other allergens) as they circulate past an array of electrically-charged stainless steel blades. Have students research air cleaners, air purifiers, copy machines and printers that use similar technology to the industrial electrostatic precipitators.

Activity Scaling

• Although this activity is appropriate for all age levels, younger students may need assistance blowing up balloons.
• For upper grades, add a math component. Give students a number of particulates, and have them calculate how many are cleaned from the air using electrostatic precipitators with 98% efficiency. For example, if 100,000 particulates went through this electrostatic precipitator, about 100,000 x .98 = 98,000 would be removed, and 2,000 would remain.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.