The setup consists of a brass tube fitted in a rectangular duct in a vertical position. The duct is open at the top and bottom, and forms an enclosure that serves the purpose of undisturbed surrounding. One side of the duct is fitted with a transparent acrylic window for visualization. An electric heating element is kept in the vertical tube that in turns heats the tube surface. The heat is lost from the tube to the surrounding air by natural convection.

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