Flow Visualisation Apparatus Technical Description The experimental set-up is used in combination with the Air Flow Bench to make flow lines around bodies visible. A smoke generator evaporates liquid paraffin, the smoke is blown via a slotted tube into a vertical smoke duct. A viewing window fitted to the front of the smoke duct enables the interior of the duct to be observed with ease. The inside of the duct is black to make the flow lines easier to see. The flow around bodies can be investigated using various models.