Experimental Studies and Correlations of Radially Outward and Inward Air-Flow Heat Transfer in a Rotating Square Duct

Experiments were conducted to investigate the convective heat transfer of radially outward and inward air flows in a uniformly heated rotating square duct. The interior duct surfaces, constructed by fiberglass-reinforced plastic, were plated with separated film heaters for distinguishing the local wall heat transfer rate. The duct hydraulic diameter, the actively heated length, and the mean rotation radius are 4, 120, and 180 mm, respectively. In the experiments, the parameters were the throughflow Reynolds number, Re = 1,000∼15,000; the rotation number, Ro = 0∼0.32; and the rotational buoyancy parameter, Ra* = 0∼0.5. For the outward flow the Coriolis-induced cross-stream secondary flow strongly enhanced the heat transfer on the leading edge. But for the radially inward flow the trend was reversed. When the throughflow Reynolds number was increased, the rotating-buoyancy decreased, then increased the heat transfer for the outward flow; however, the rotating-buoyancy always increased the heat transfer for the inward flow. The heat transfer data are correlated for the outward and inward flows for the ranges of parameters under study.