PURPOSE: To dramatically illustrate laminar flow by "unmixing" two fluids.
DESCRIPTION: Glycerine forms a cylindrical shell between two plexiglass cylinders. The inner cylinder can be rotated, setting up a laminar flow in the glycerine. Using a long hypodermic syringe, blue dye is injected in a line in the glycerine midway between the two cylinders, as shown in the left photo. Clicking the lower photo shows a short movie of the dye injection process. As the inner cylinder is rotated several turns, the dye "mixes" with the glycerine, as seen in the center photo. When the rotation is reversed, the dye "unmixes" and almost returns to its original state, as seen in the photo at the right. Short videos are avaiable showing the mixing and unmixing process in either the clockwise or anticlockwise direction.
Click here for a schematic of our unmixing apparatus. (Requires Adobe Acrobat.)SUGGESTIONS: Follow directions provided carefully for filling the syringe and making the line.
REFERENCES: (PIRA unknown.) See "UNMIXING DEMONSTRATION" videotape in our library. The Demonstration Reference File includes articles on this device and information and drawings for its construction.
EQUIPMENT: Unmixing apparatus, hypodermic syringe with dye mixture.
SETUP TIME: 5 min.
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