HEAT TRANSFER FROM A DISCRETE HEAT SOURCE IN CONFINED AIR JET IMPINGEMENT

The local heat transfer from a square heat source to single, axisymmetric, confined air jets was experimentally investigated. The jets issued from short, square-edged orifices with a still-developing velocity profile on to a foil heat source that produced a constant heat flux. The orifice plate and the surface containing the heat source were mounted opposite each other in a parallel-plates arrangement to effect radial outflow of the spent fluid. The local surface temperature was mapped as a function of the jet Reynolds number (5000≤Re≤20000), orifice-to-heat source spacing (0.5≤H/d≤4), and orifice diameter (1.59≤d≤12.7 mm). For the larger diameter jets, the stagnation heat transfer coefficient decreased with decreasing H/d and secondary peaks in the heat transfer coefficient were observed. In contrast, the stagnation heat transfer coefficient for the smaller diameter jets increased with decreasing H/d, and secondary peaks were not present. Predictive correlations for the stagnation and average Nusselt numbers are presented.