One of the best ways to understand convection currents is to witness it with your own eyes. The Wind Tunnel Convection demonstration lets you do just that. As the air is heated by the candle, it expands and becomes lighter and rises up the vertical chimney. The evacuated air is replaced by cooler air which is pulled into the convection current through the horizontal chimney. As the convection current cycles, the fans, which are positioned on each end of both chimneys, begin to spin. This creates a visual demonstration of the convection current. For additional visibility, you can add a small amount of smoke to the convection current.