Description
A Couette Cell demonstrates the principles of entropy and the second law of thermodynamics by visually showcasing the concept of mixing and unmixing. The apparatus consists of two concentric cylinders with a Newtonian fluid, such as glycerin, and a tracer dye between them. When the inner cylinder rotates, the dye appears to mix, creating a fine spiral pattern. By reversing the rotation, the dye seemingly "unmixes," returning to its original configuration. This reversible process highlights the distinction between ordered and disordered states, providing a compelling visual representation of entropy and the inherent directionality of natural processes as dictated by the second law of thermodynamics.
Aliases
Couette Cell
PIRA DCS Number
4F10.10
Preparation & Instructions
The mixing/unmixing demonstration uses around 1.75 liters of Karo light corn syrup, and must be set up in 2 phases, ideally separated by 8 hours. This gives the corn syrup time to release all of the air bubbles and become clear. Additionally, the dyed corn syrup should be injected shortly before the demo is to be presented to prevent the lines from getting mixed or blurred.
Phase 1: Preparation
- Using alcohol wipes, make sure the couette cell is clean inside and out
- Fill couette cell with 1.75 liters of Karo light corn syrup
- Install the inner cylinder by slowly guiding the bottom pivot point down into the center of the respective outer cell’s bottom pivot point.
- Install the 6 bolts hand tight making sure to tighten them evenly
- Wait 8+ hours
Phase 2: Drawing Lines with the Syringe & Presentation
- Locate the 2 syringes, each with a different color of dyed Karo light corn syrup. If they are empty or don’t contain enough dyed corn syrup, new dyed syrup must be mixed and retrieved with the syringes.
- Attach the small hose & glass tube to one of the syringes
- Squeeze the syringe until the glass tube is completely full of dyed syrup.
- Using the hole on the top of the outer cylinder of the couette cell, dip the end of the glass tube directly into the corn syrup and begin injecting the dyed syrup from bottom to top, in a straight line. NOTE: if 2 lines are to be drawn (with different colors), the syringe must be angled left or right.
- Once the glass tube is almost out of the corn syrup, retract the syringe plunger to pull some undyed syrup into the glass tube.
- Remove the syringe, and repeat with the other if desired. NOTE: the glass tube must be completely purged of previous dyed corn syrup to prevent cross-contamination of colors.
Bonus Phase: Cleaning
- The used corn syrup from the couette cylinder cannot be washed down the drain, but should be placed in a waste disposal container and marked with the chemical name and quantity.
- The syringes can be left with dyed corn syrup if there is some left over.
- The small hose & glass tube should be rinsed with hot water until completely clear.