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首页> 外文期刊>International Journal of Heat and Mass Transfer >Effectiveness and heat transfer characteristics for a single heated rectangular jet with different aspect ratios impinging perpendicularly on a flat surface
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Effectiveness and heat transfer characteristics for a single heated rectangular jet with different aspect ratios impinging perpendicularly on a flat surface

机译：不同纵横比垂直入射在平面上的单个加热矩形射流的效率和传热特性

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摘要

Results from an experimental investigation to study the distribution of local effectiveness and Nusselt number for a heated rectangular jet with different aspect ratios impinging perpendicularly on a flat surface are reported here. The jet exits from a rectangular nozzle of height 'H' and width 'W with a developing length equal to 50 times the hydraulic diameter of the nozzle geometry, b. Nozzle aspect ratios, H/W, equal to 10,5 and 1, Reynolds numbers (based on average exit velocity of jet and hydraulic diameter of nozzle) equal to 11,000 and 17,000 and non dimensional jet-to-plate distances, L/b, equal to 2,3,4 and 5 were studied. The contours of effectiveness and Nusselt number are initially similar to the exit shape of the nozzle but very quickly take the shape similar to that of a rhombus with rounded comers with diagonals along the major and minor axes of the rectangular jet. The effectiveness variations show that after impingement, the jet fluid entrains the surrounding fluid from the edges as well as the top surface. The edge entrainments progress towards the center, giving the contours the characteristic 'rhombus like' shape. The Nusselt number is also influenced by the fluid entrainment, as indicated by the contours. Regions of high heat transfer coefficients are observed due to high turbulence generated by mixing with the stagnant ambient, especially at the low L/b ratios.
机译：本文报道了一项实验研究的结果，该结果研究了加热的矩形喷射流的局部有效性和Nusselt数的分布，该矩形喷射流具有不同的长宽比，垂直入射在平坦的表面上。射流从高度为“ H”且宽度为“ W”的矩形喷嘴中流出，展开长度等于喷嘴几何形状b的水力直径的50倍。喷嘴纵横比H / W等于10.5和1，雷诺数（基于喷嘴的平均出口速度和喷嘴的水力直径）等于11,000和17,000，无量纲的喷嘴到板的距离L / b等于2,3,4和5。效果和Nusselt数的轮廓最初类似于喷嘴的出口形状，但很快就变成类似于菱形的形状，菱形带有圆角，沿矩形射流的长轴和短轴呈对角线。有效性变化表明，撞击后，喷射流体会从边缘以及顶面夹带周围的流体。边缘夹带朝向中心前进，使轮廓具有特征性的“菱形”形状。如轮廓所示，努塞尔数也受流体夹带的影响。由于与停滞的环境混合而产生的高湍流，尤其是在低L / b比的情况下，观察到了高传热系数的区域。

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