Turbulent heat transfer coefficients and fluid flow patterns on the faces of a centrally positioned blockage in a duct

Experiments encompassing both heat-transfer measurements and flow visualization were performed for turbulent flow in a square duct whose cross section was partially obstructed by a centrally positioned transverse blockage. Heat-transfer coefficients were obtained for both the upstream and downstream faces of the blockage element. The flow visualization, performed with the oil-lampblack technique, revealed the presence of three stagnation zones on the upstream face. The downstream face is washed by highly complex recirculation zones, characterized by sidewise fluid motions (along the span of the blockage). Heat-transfer coefficients on the upstream face generally increase with the square root of the Reynolds number; at a given mass flow, higher coefficients are in evidence at smaller blockage heights. The downstream-face coefficients display a complex dependence on both the blockage height and the Reynolds number. In the main, for the Reynolds number range investigated, the upstream-face coefficients are greater than the downstream-face coefficients. Comparisons with the literature showed that the coefficients for a centrally positioned blockage exceed those for a wall-attached blockage by as much as a factor of two.