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

当旋转滚筒或圆柱体冷却时，通常采用外表面上的翅片阵列结构作为延伸表面以改善散热性能。在这种情况下，与没有翅片的滚筒相比，由于翅片的搅动效应，传热系数也会增加。然而，关于这种类型的传热系统的传热特性的信息很少。为了获得高热流密度条件下带肋片的旋转滚筒与周围空气的对流换热特性，并阐明其换热机理，进行了两个主要实验：（1）传热实验，获得高热流密度、高转速条件下翅片阵列转鼓的排热性能和平均传热系数，（2）不可逆温敏涂料的实验， ...更多信息 的翅片表面上，以获得翅片表面上的温度分布和局部传热系数的信息。在本研究中测试的滚筒由钢制成并且具有326 mm的外径，在该滚筒上布置有具有15 mm高度的翅片的翅片阵列。实验通过使用旋转体的传热实验装置进行，在不同的旋转速度（高达2400 prm）下改变翅片布置（翅片间距、翅片角度和翅片厚度）。本研究获得的结果如下。（1）与没有翅片的滚筒相比，翅片表面的传热增强。在相同转速下，翅片角为30°的鼓形结构的强化效果最好，约为无翅片圆筒的3.5倍。换热系数随转速的0.70次方单调变化，但其比例因子随翅片排列方式的变化较为复杂，即，翅片间距和翅片角度。（2）该系统的传热由以下三种机制组成：（a）通过相邻翅片的通道流;（B）翅片顶部的空腔流;（c）离心力引起的自然对流。这三种机制对传热贡献的大小导致了翅片阵列转鼓的传热特性复杂。最后，根据上述结果提出了无量纲传热关联式。少

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