HEAT-TRANSFER CHARACTERISTICS OF AN AXISYMMETRICAL JET IMPINGING ON A WALL WITH CONCENTRIC ROUGHNESS ELEMENTS

An impinging jet produces a high heat transfer coefficient in the stagnation region by a conventional procedure; an axisymmetric impinging jet has practical applications and produces a higher heat transfer coefficient than does a two-dimensional impinging jet. This high heat transfer coefficient decreases rapidly with the streamwise distance from the stagnation region. Since most of the heat transfer area is located in the downstream region, the heat transfer augmentation of the broad downstream region is a prime target through which to achieve high heat transfer performance. Large-scale concentric repeated roughness on heat transfer surfaces was created to carry out the augmentation for an axisymmetric, submerged, impinging air jet. The investigation was made to measure the local heat transfer coefficients over rough surfaces by varying jet velocity as well as to investigate of the flow structure using the visualization technique.