喷雾液滴撞击大豆叶片表面研究

Impact of Spray Droplet on Soybean Leaf Surface

摘要:

利用两台高速数码摄像机对喷雾液滴撞击大豆叶片表面过程和结果进行了测试与分析。研究结果表明，产生沉积和回缩破碎两种状态时，液滴K值均小于57.7；发生喷溅时，大部分液滴K值大于57.7，但由于叶片表面密被长柔毛使得液滴在低撞击角度下易于喷溅，因此液滴在撞击角度为28°和44°时K值小于57.7。液滴在沉积过程中，在相同粒径和撞击角度下，液滴撞击速度越高最大铺展越大，铺展时间也越长，但撞击速度高和撞击速度低的液滴最终铺展比接近。沉积部位对液滴铺展过程和结果有重要影响。液滴在回缩破碎过程中，在表面张力的回缩和叶片表面的粘滞作用下分离破碎，与沉积于叶片表面的液滴相比较，液滴收缩破碎后合计最终铺展比大大提高，均匀破碎的液滴其合计最终铺展比比不均匀破碎的液滴大。当撞击We数较高时，喷溅液滴将呈现喷射成串小液滴的状态；当撞击We数较低时，喷溅液滴将呈现喷射单独的2~3个大液滴的状态。喷射出成串小液滴后的液滴主体部分最终铺展比比喷射出单独大液滴后的液滴主体部分大。

Abstract:

This study used two high speed digital cameras to test and analyze the process and result of spray droplet impact on the soybean leaf surface. The result showed that when spray droplets were deposited and rebound broken, K values were less than 57.7. When splashing, K values of the most droplets were more than 57.7 because of the dense pilose of the leaf surface. The droplets were splashed easily at a low impact angle. K values were less than 57.7 when impact angles were 28° and 44°. Considering the same particle size and impact angle in the deposited droplets, the maximum spreading increased and the spreading time prolonged with increasing impact velocity. The final maximum spreading ratio of the high impact velocity was close to the low impact velocity. Deposit locations significantly influenced the process and result of the droplet spreading. In the process of receding break up, the droplets separated and were broken under the rebound action of the surface tension and viscosity of the leaf surface. Compared with the droplets deposited on the leaf surface, the total final maximum spreading ratio of the droplets enlarged greatly after receding break up. The total final maximum spreading ratio of uniform droplets was larger than that of nonuniform droplets. When Weber number (We) of the impact was high, the spray droplets appeared as a series of small droplets. When We was low, the spray droplets appeared as two to three large droplets. The final maximum spreading ratio of the main body of the droplets after spraying a series of small droplets was larger than that when individual large droplets are sprayed.