Abstract:

Experimental study on mixing dynamic characteristics during down-flow spraying water into air at different speeds was carried out. The spray pressure varied between 0.1—1.5 MPa, and air speed between 14.6 m?s^-1 and 46.2 m?s^-1. The mix chamber was a transparent rectangle channel with cross section of 70 mm×70 mm. The velocity field and initial droplets size distribution were respectively measured by high speed photography and Malvern particle size meter. Results suggested that spray pressure mainly affected radial velocity and the axial velocity alongside spray axis. While the air speed mainly affected the axial velocity at outside boundary of plume. The mean axial velocity was introduced and used as the reference velocity for mixing. It was found increased with increasing spray distance or spray pressure. The initial particle size decreased with decreasing spray pressure or increasing relative velocity between air and water at nozzle exit. According to above experimental results, correlations for the mean axial velocity and initial droplet size was set up. The relative error between calculated and experimental results mainly fell within ±15%.

Key words: finite channel, atomization, down-flow spray mixing, velocity field, particle size distribution

摘要：

设计搭建了有限截面通道顺流喷雾掺混实验台，在横截面为70 mm×70 mm的透明方形掺混段内，将室温水经喷嘴雾化后顺流掺入不同流速的室温空气。实验中，喷水压力为0.1～1.5 MPa，风速为14.6～46.2 m?s^-1。分别采用高速摄影和马尔文粒度仪对该雾羽的速度场和初始粒径等动力学特征开展了实验研究。结果指出：掺混雾羽的径向速度及喷射轴线附近的轴向速度主要受制于喷水压力；而雾羽两翼处的轴向速度主要受风速影响。定义轴向平均速度为雾羽轴向特征速度，该平均速度随喷水压力或喷射距离的增大而增大；在喷水压力小时，风速的增大可使轴向平均速度随喷射距离增大的速率提高；在喷水压力高时则反之。掺混雾羽的初始粒径随喷水压力的减小或喷嘴出口处气液相对速度的增大而减小。最后，根据实验结果拟合了轴向平均速度和初始粒径的实验关联式，其计算值与实验值吻合良好。

关键词: 有限通道, 喷雾, 顺流掺混, 速度场, 粒径分布