管内周期性自旋流强化传热的结构优化

在圆管内间隔插入多个旋流片的流道中，流体流动呈现周期性自旋流.用数值模拟方法对空气湍流情况的传热和流阻性能受相邻旋流片间距L_p、旋流角β和旋转角α3个因素的影响进行了分析，并得出旋流片的优化结构，而且实验验证了数值模拟预测的正确性.结果表明：α越大，传热性能越好，阻力越大;L_p越小，传热性能越好，阻力越大;β越大，传热性能越好，而阻力损失因受到摩擦阻力和形体阻力的综合影响而呈现非单调变化.旋流片的最佳结构参数为：旋流角β为20.3°，旋转角α为180°，相邻旋流片间距L_p为33d.与α相比，β对传热和流阻性能的影响更显著.

Structural optimization of twisted-leaves based on heat transfer enhancement for periodic free swirl flow in tube

The influences of twisted-leaf piech L_p,swirl angle β and twist angle α on the characteristics of heat transfer and flow resistance of plain circular tube with inserted twisted-leaves discontinuously for air turbulent flow were analyzed in detail by numerical simulation and the optimized structure of the twisted-leaves was obtained based on heat transfer enhancement valuation factor η.In addition, the numerical simulation predictions were verified by experiment.The results indicated that the larger the α, the better the performance of heat transfer and the greater the flow resistance; the larger the L_p, the worse the performance of heat transfer and the smaller the flow resistance; the larger the β, the better performance of heat transfer while the variation of flow resistance was not monotone because of the combined control of friction resistance and shape drag.The optimized structure parameters of twisted-leaf were swirl angle β=20.3°,twist angle α=180°,twisted-leaf pitch L_p=33d（d means the width of twisted-leaf）.Furthermore, compared with twist angle α, the influence of swirl angle β on heat transfer enhancement was much stronger.