Shroud Heat Transfer Measurements From a Rotating Cavity With an Axial Throughflow of Air

Abstract

The paper discusses measurements of heat transfer obtained from the inside surface of the peripheral shroud. The experiments were carried out on a rotating cavity, comprising two 0.985m diameter discs, separated by an axial gap of 0.065 m and bounded at the circumference by a carbon fibre shroud. Tests were conducted with a heated shroud and either unheated or heated discs. When heated, the discs had the same temperature level and surface temperature distribution. Two different temperature distributions were tested; the surface temperature either increased, or decreased with radius. The effects of disc, shroud and air temperature levels were also studied. Tests were carried out for the range of axial throughflow rates and speeds: 0.0025 ≤ m ≤ 0.2 kg/s and 12.5 ≤ Ω ≤ 125 rad/sec, respectively. Measurements were also made of the temperature of the air inside the cavity. The shroud Nusselt numbers are found to depend on a Grashof number which is defined using the centripetal acceleration. Providing the correct reference temperature is used, the measured Nusselt numbers also show similarity to those predicted by an established correlation for a horizontal plate in air. The heat transfer from the shroud is only weakly affected by the disc surface temperature distribution and temperature level. The heat transfer from the shroud appears to be affected by the Rossby number. A significant enhancement to the rotationally-induced free convection occurs in the regions: 2 ≤ Ro ≤ 4 and Ro 4 ≥ 20. The first of these corresponds to a region where vortex breakdown has been observed. In the second region, the Rossby number may be sufficiently large for the central throughflow to directly affect the shroud heat transfer. Heating the shroud does not appear to significantly affect the heat transfer from the discs.