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对横掠不同长径比的椭圆管的换热和流动特性进行了研究。实验过程中考虑了8种不同类型的椭圆管,流动介质为空气。通过热质比拟和萘升华技术,获得了雷诺数在7000~65000范围内的局部和平均对流换热系数,通过比较不同类型椭圆管的实验结果,阐明了长径比k的影响,首次给出了Nu=f(k,Re,Pr)形式的实验关联式。同时,通过实验还获得了流动阻力系数。最后,使用油-灯黑可视化技术对横掠椭圆管的绕流特点进行了显示。结果表明,局部对流换热系数随长径比k变化,边界层的分离点随k的增大而向后移动。当k<6.0时,椭圆管的平均对流换热系数高于圆管;当k=6.0时,达到最大值,大约为圆管的1.6倍,同时,其阻力系数随着k的增大而减小;当k=2.0时,阻力系数约为圆管的60％。流型印证了实验结果的合理性。
The heat transfer and flow characteristics of elliptical tubes with different aspect ratios were studied. Eight different types of oval tubes were considered during the experiment, and the flow medium was air. Through the comparison of thermal mass and naphthalene sublimation technology, the local and average convective heat transfer coefficients with Reynolds number in the range of 7000-65000 were obtained. The effect of aspect ratio k was clarified by comparing the experimental results of different types of oval tubes. The experimental correlation in the form Nu = f (k, Re, Pr). At the same time, through the experiment also obtained the flow resistance coefficient. Finally, the oil-lamp black visualization technique was used to characterize the flow around the swept elliptical tube. The results show that the local convective heat transfer coefficient changes with the aspect ratio k, and the separation point of the boundary layer moves backward with the increase of k. When k <6.0, the average convective heat transfer coefficient of elliptical tube is higher than that of circular tube. When k = 6.0, the maximum value is reached, which is about 1.6 times of that of circular tube. At the same time, the drag coefficient decreases with the increase of k Small; when k = 2.0, the drag coefficient is about 60% of the tube. The flow pattern confirms the rationality of experimental results.