(Small class, or use video camera for large class)
The trick is to use a viscous fluid to view patterns with structrure. In water the Rayleigh number is so high that it is hard to visualize relatively simple states.
Pour a layer of 100cs silicone oil laced with aluminum flakes for visualization into the fry pan. Use the aluminum disc to more evenly distribute the heat. Turn the hot plate on to low or medium.
Typical pattern. Change layer depth by adding more fluid, or tilt the pan, to show that cell size ~ depth.
Radial motions in at the top and out the base form a flow with vertical shear. This shear can align the convection radially.
©2000. John Hart, University of Colorado