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Forced Convective Heat Transfer Enhancement by the Turbulent Promoter Generating Streamwise Vortices

湍流促进器产生流向涡流增强强制对流换热

基本信息

批准号：
61550150
负责人：
HIJIKATA Kunio
金额：
$ 1.15万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

The flow characteristics and the heat transfer performances of such pipes have been reported by many authors, but all of these reports treated the repeated-rib roughness where the ribs were set perpendicular to the pipe axis. Since the flow in the pipe with this promoter is greatly accelerated in the front part of the promoter, the pressure loss also increases. In the light of reducing the pressure loss and getting higher heat transfer performance, the inclined repeated-rib roughness are proposed in this paper, namely the ribs are set not perpendicular but inclined to the pipe axis. The pipe with this type of promoter is considered to have two kinds of advantages. One advantage is smaller flow contraction ratio of the cross sectional area due to the promoter, compared with that of the normal repeated-rib roughness. The other is that the inclined repeated-rib produces the secondary flow in the pipe which enhances the heat transfer performance of the pipe.The mechanism of the generation of secondary flow was quantitatively investigated from the measured velocity profile by considering the contribution of the advection terms of the N.S. equation. The intensity of the secondary flow did not depend on the Reynolds number and the maximum velocity of the secondary motion was over 45 percent of the mean axial velocity of the pipe in the Reynolds nember region from 3500 to 20000. The detailed structure of the flow was claified by the LDV, and it is concluded that the measured Reynolds stress is accurately correspond to the velocity gradient and the eddy diffusivity assumption is applicale.The flow resistance of the pipe with the inclined repeated-rib roughness evaluated by the roughness fuction was lower than that with normal repeated-rib, which means that the inclined repeated-rib roughness has great adavatage in a practical usage.

这类管子的流动特性和换热性能已被许多作者所报道，但这些报道都是针对肋片垂直于管轴的重复肋片粗糙度。由于加入该助力器的管内流动在助力器前部大大加速，压力损失也随之增大。从减小压力损失和获得较高换热性能的角度出发，本文提出了倾斜的重复肋粗糙度，即肋条不垂直于管轴，而是倾斜于管轴。这种类型的促进剂管道被认为有两种优点。一个优点是，与正常的重复肋骨粗糙度相比，由于助推器的作用，横截面面积的流动收缩比更小。另一种是倾斜的重复肋片在管内产生二次流，强化了管内的换热性能。根据测量的速度分布，考虑NSS方程的平流项的贡献，定量地研究了二次流的产生机理。二次流的强度与雷诺数无关，在雷诺数为3500~20000的范围内，二次流的最大速度超过管轴向平均速度的45%以上。利用LDV对流动的详细结构进行了描述，结果表明，测量的雷诺应力与速度梯度有较好的对应关系，并采用了涡流扩散系数假设；采用粗糙度函数估算的倾斜重复肋粗糙度管道的流动阻力比常规重复肋粗糙度低，这说明倾斜重复肋粗糙度在实际应用中具有较大的优势。