Local heat (mass) transfer in a rotating square channel with ejection holes
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The objective of this experimental investigation was to examine the effects of rotation, flow ejection, channel orientation, and transverse ribs on the local heat (mass) transfer distribution for radial outward flow in a square channel, rotating about a perpendicular axis. The test channel was oriented so that the direction of rotation was perpendicular or at a 45 angle to the leading and trailing walls. There were eight ejection holes along the leading or trailing walls of the test channel. The diameter of each ejection hole was equal to one-fifth of the channel hydraulic diameter. The wall with the ejection holes was either smooth or roughened with seven transverse ribs. Each rib was located midway between two ejection holes. The height of the ribs was equal to one-tenth of the channel hydraulic diameter, and the spacing between two ribs was equal to ten times the rib height. The test channel modeled coolant passages with film cooling holes in modern gas turbine blades. The Reynolds number was 5,500 and the rotation number range was between 0.0 and 0.24. In a smooth normally-oriented channel, rotation in the direction of the ejection flow significantly reduces the local heat/mass transfer on the leading wall, except in the vicinity of the ejection holes. Rotation in a direction opposite to that of the ejection flow widens the high heat/mass transfer regions near the ejection holes, and reduces the heat/mass transfer in the regions between ejection holes on the trailing wall. In a smooth diagonally-oriented channel, the trend of higher heat/mass transfer near the leading side of the leading wall than near the trailing side is the opposite of the expected trend for radial outward flow through a smooth diagonally-oriented channel with no ejection holes. Flow reattachment downstream of the transverse ribs and flow acceleration toward the ejection holes together cause very high heat/mass transfer in bell-shaped regions around the ejection holes. Rotation in a diagonal direction changes the shape of the local heat/mass transfer distribution more on the leading wall than on the trailing wall of a rib-roughened channel.
