冠齿喷嘴射流冲击平直靶面对流换热实验

利用红外热像仪测试了冠齿喷嘴射流冲击平直靶面的对流换热特性，在射流雷诺数为5 000~20 000、冲击间距比为1~8范围内，与普通圆管射流进行了对比，并对冠齿数和冠齿长度的影响进行了初步分析。研究结果表明，冠齿射流冲击对流换热显著高于圆形射流，在小冲击间距下，冠齿射流冲击的局部对流换热系数分布在冲击驻点附近呈现明显的梅花瓣状特征，当射流冲击间距比达到4以后，冠齿射流的局部对流换热系数分布则呈现出常规圆形射流冲击的特征；以2倍或4倍射流直径作为区域平均范围，冠齿射流的区域平均努塞尔数相对圆形射流的增加幅度在15%~30%之间，相对增加幅度与射流雷诺数和射流冲击间距比相关；在本文的冠齿结构参数范围内，冠齿伸出长径比为0.6的6-冠齿结构取得的射流冲击强化传热效果较优。

Experimental of chevron nozzle jet impingement heat transfer on flat targeting surface

An experimental investigation of chevron nozzle jet impingement heat transfer on a flat surface was performed by using the infrared camera. The tests were conducted with typical Reynolds numbers ranging from 5 000 to 20 000 and dimensionless nozzle-to-surface distances ranging from 1 to 8. A comparison with the round nozzle jet was made, and the geometric effects of the chevron nozzle were analyzed. The results show that the chevron nozzle plays a significant role in improving jet impingement heat transfer. At small impinging distances, the distribution of local convective heat transfer produced by the chevron-jet shows an obvious lobe-shaped feature in the vicinity of the impinging stagnation point. When the dimensionless nozzle-to-surface distance is beyond 4, distribution of local convective heat transfer produced by the chevron-jet is similar to that by the round jet. The averaged Nusselt number of the chevron nozzle jet area of either 2 or 4 times of the nozzle diameter for average achieves 15%-30% increase compared to that of the round nozzle jet, and the increase depends on the jet Reynolds number and dimensionless nozzle-to-surface distance. For the current geometric parameters of the chevron nozzle, it is found that the 6-chevron nozzle with a chevron length-to-nozzle diameter of 0.6 can produce more favorable heat transfer enhancement.