Glue a cup onto the center of a square piece of wood so there is at least 6 inches of wood on any given side of the cup. Glue the first vinyl sheet to the side of the cup, then make a semi-circle with it about 2 inches outside of the cup. Glue the sheet's edge to the wood surface. The sheet will look like a "c" surrounding the cup from a top view. Directly opposite of the place where the first sheet is glued to the cup, glue the second sheet. Make a semi-circle around the cup with that sheet, as well, on the opposite side. Cut a hole two inches in diameter in a clear plastic plant saucer, and set it aside for later.
Pour 1/2 cup of water into the cup. Put on gloves, and place a few pieces of dry ice in the cup with the water. The water will warm the ice enough to start forming a cool gaseous carbon dioxide. As that carbon dioxide rises above the cup, it will cause water vapor to condense into a cloud into the air.
Place the plant saucer on top of the two pieces of vinyl so that it seals the top of the cup. The saucer should fully cover the vinyl sheet semi-circles. Place the fan in the hole cut into the saucer and turn it on to draw the air, at all its various temperatures, up and out of the system. You should see a vortex form and a tornado start to spin. The fan is creating a spinning updraft that you will be able to see as the visible condensation vapor cloud is sucked out of the system.