Experiments with particle settling

Elana Leithold, North Carolina State University at Raleigh
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Initial Publication Date: June 3, 2014 | Reviewed: June 24, 2014


In this activity, students experiment with the effects of Reynolds numbers (viscosity), particle shape, and particle concentration (flocculation) on settling velocity.

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This is a laboratory activity used in an upper level undergradate/beginning graduate course on sediment transport. It is deliberately simple, and could be appropriate for a lower level course as well. The course is scheduled for a 75 minute period twice weekly (there is no separate laboratory section), so it is designed to fit into that time slot.

Skills and concepts that students must have mastered

The students have had an introduction to fluid viscosity and Reynolds numbers. The lab also typically follows lectures about calculating settling velocities and potential complications (including flocculation), but this lab could be an introduction to those topics as well (coming before lecture material or problem sets about settling velocity).

How the activity is situated in the course

This is one of five laboratory exercises in my sediment transport class.


Content/concepts goals for this activity

The goals of this exercise include giving students experience with the effects of viscosity and particle shape on particle setting. The effects of particle concentration on flocculation and settling are also explored.

Higher order thinking skills goals for this activity

Students gain experience with collecting data (including replication), as well as graphing and interpreting results.

Other skills goals for this activity

Students work in small groups and as a class to collect data using glassware, stop watches, and turbidity meters.

Description and Teaching Materials

The class is divided into small groups of 3-4 for this activity. The groups rotate between stations. Materials needed include:
  1. graduated 1000 mL cylinders
  2. clear dish liquid
  3. Borosilicate glass beads (available from scientific suppliers for chromotography)
  4. Stop watches
  5. Plastic clay (e.g. Sculpey), previous baked
  6. Salt
  7. Kaolinite clay (available from scientific suppliers)
  8. Stir rods for 1000 mL cylinders
  9. 10 mL volumetric pipettes and filler bulbs
  10. A portable turbidity meter and glass vials (I own two LaMotte 2020we Turbidity Meters)
  11. Squeeze bottles
  12. Kimwipe or similar lint-free tissues
Student handout for Settling Lab (Microsoft Word 134kB Jun3 14)

Teaching Notes and Tips

I set this up as a series of stations that groups rotate to.

For the first part, it is best to pour dish liquid into cylinders the night before so that it can debubble

For part 3, prepare salt solution for each cylinder by dissolving 30 gm of NaCl in 1 L of DI water

The kaolinite is commonly "clumped" when first purchased, so it is important to make sure the particles will settle individually. I use a sonicator probe to break the kaolinite up, but if that isn't available, grinding might work. I weigh out 1.8 gm, 0.18 gm, and 0.018 gm of kaolinite into 150 mL beakers and add 50 mL DI, sonicate with a Branson ultrasonic probe at 20% amplitude for 60 sec. The day before the lab activity, I add the slurry to the salt water in the cylinders and homogenize the contents with a stir rod.


The students hand in the lab activity for grading at the beginning of the next class meeting.

References and Resources