A Study on Mechanisms of Convective Heat Transfer from a Rotating Drum with Fin Array under High Heat Flux Conditions.

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When a rotating drum or cylinder is cooled down, a fin array structure on the outer surface is often adopted as an extended surface to improve the heat removal performance. In this case it is also expected that the heat transfer coefficient increases due to an agitation effect by the fins compared with that for the drums without fins. However, there is very little information on the heat transfer characteristics for this type of heat transfer system. This study aimed to obtain experimentally the convective heat transfer characteristics from the rotating drum with fin array to ambient air under high heat flux conditions, and to clarify the heat transfer mechanisms.Two major experiments were performed : (1)the heat transfer experiment to obtain the heat removal performance and average heat transfer coefficients of the rotating drum with fin array for high heat flux and high rotating speed conditions, and (2)the experiment using the irreversible temperature-sensitive paints, which were pa … More inted on the fin surface, in order to obtain the temperature profiles on the fin surface and the information on the local heat transfer coefficients. The drum tested in this study was made of steel and had an outer diameter of 326mm, on which the fin array was arranged with fins having a height of 15mm. The experiments were performed by using a heat transfer experiment setup for rotating body, with changing fin arrangement (fin pitch, fin angle, and fin thickness) under various rotating speeds (up to 2400prm). The results obtained in this study were as follows.(1)The heat transfer of the finned surface is enhanced compared with the drum without fins. The highest enhancement is obtained for the drum with the fin angle of 30° ; and is about 3.5 times as high as that of the cylinder without fins for the same rotating speed. While the heat transfer coefficient monotonically varies with rotating speed to the power of 0.70, its proportionality factor changes complexly with fin arrangement, i.e., fin pitch and fin angle.(2)The heat transfer of this system consists of the following three mechanisms (a)channel flow passing through the adjacent fins, (b)cavity flow over the tops of the fins, and (c)natural convection induced by the centrifugal force, which is not negligible under the high temperature surface condition at the high heat flux. The magnitude of contribution of these three mechanisms to the heat transfer causes the complex heat transfer characteristics of the rotating drum with fin array.Finally, non-dimensional heat transfer correlations were proposed from the above results. Less