THE PHYSICAL MECHANISM FORMELT PULSATION DURING CLOSE-COUPLED ATOMIZATION
THE PHYSICAL MECHANISM FORMELT PULSATION DURING CLOSE-COUPLED ATOMIZATION
复制标题
紧耦合雾化过程中形成熔体脉动的物理机制
作者：
A. Mullis
用高速薄膜(18000帧/秒)研究了离散射流高压气体雾化系统中的熔体脉动现象。已经开发了图像处理程序来确定熔体羽流内的材料从熔体输送喷嘴流出时的速度，并对熔体羽流的形状进行参数化。然后将这些数据与熔体羽流中的材料体积相关联，这被用作熔体脉动的诊断。我们发现，在低熔体时期，直径最小的熔体羽流中的收缩较小，且向下游较远。两者似乎都符合从高熔体流动时期的开放尾迹结构到低熔体流动时期的闭合尾迹结构的转变。此外，在低熔体流动期间，羽流中物质的平均速度似乎下降，我们将其归因于它通过马赫盘。我们的结论是，有足够的证据表明，在向雾化器引入稠密的第二种流体后，闭合尾迹条件仍然存在，开放和闭合尾迹条件之间的交替可能是观察到的熔体脉动的原因。
High speed filming (18000 fps) has been used to study the phenomenon of melt pulsation in a discrete jet, high pressure gas atomization system. Image processing routines have been developed to determine the velocity of material within the melt plume as it streams away from the melt delivery nozzle and to parameterise the shape of the melt plume. This data is then correlated with the volume of material in the melt plume, which is used as a diagnostic for melt pulsation. We find that during periods of low melt the constriction in the melt plume in which its diameter is a minimum is smaller and further downstream. Both appear to be consistent with a transition from an open-wake structure during periods of high melt flow to a closed-wake during periods of low melt flow. Moreover, the average velocity of material in the plume appears to drop during periods of low melt flow, which we ascribe to its passage through the Mach disk. We conclude that there is sufficient evidence to assert that the closed-wake condition survives the introduction of a dense second fluid to the atomizer and that alternation between the openand closed-wake condition is the likely cause of the observed melt pulsation.