Abstract
The heat transfer of natural convection from upward facing-horizontal heated surface which a heated annular duct was placed above was investigated experimentally. The relationship of the heat transfer to the distance of between the horizontal heated surface and the heated ducts was examined. The flow fields around the heated surface and heated ducts were visualized. With decreasing the distance, the ascending flow velocity in the heated ducts becomes low and the reverse flow occurs. The heat transfer increases with decreasing the distance. Inserting a heated inner duct enhances the heat transfer.
