Rotational heat transfer in a rectangular cooling channel with compound turbulators of pin-fins and dimples

Abstract

The convective heat transfer characteristics in a rotating trailing edge channel roughened with compound turbulators of pin-fin and dimple arrays were experimentally investigated via copper plate technique. The effects of Reynolds number (Re), rotation number (Ro) and buoyancy number (Buo) on the local and averaged heat transfer for the leading and trailing walls of current pin fin-dimpled channel were studied at conditions of 12,000 ≤ Re ≤ 20,000, 0 ≤ Ro ≤ 0.89 and 0 ≤ Buo ≤ 1.32. Both the static-to-rotating Nusselt number ratio (Nu/Nus) and the normalized Nusselt number ratio (Nu/Nu0) were compared with that in a similar pin-fin channel. To examine the coupling and individual Coriolis force and centrifugal buoyancy effects in current compound channel, experiments were designed and performed with three density ratios (d.r. = 0.05, 0.08, 0.10) for each given Re and Ro. In the static cases, it was found that heat transfer at most of the measured locations was promoted by adding dimples onto the pin-fin wall, including the high radius region where the worst heat transfer level was observed in the traditional pin-fin channel. The overall averaged heat transfer was respectively enhanced by 15.8% and 21.0% at Re = 12,000 and 20,000. In the rotating compound channel, the heat transfer augmentation in the high radius region reduced with rotation, and the reduction expanded towards the low radius with ascending Ro. A turning point at each location were observed after which heat transfer stopped decreasing and started to recover with rotation. Those turning points were diverse at various locations, but they appeared to be approximately 1.0 once the local rotation number were adopted. Moreover, the heat transfer data indicated that the centrifugal buoyancy abated or promoted heat transfer at lower or higher Ro, respectively. Further study revealed that the local parameters were more instructive than the inlet ones to analyze the coupling and isolated Coriolis force and centrifugal buoyancy effects in current compound channel.