Computational analysis of drop-on-demand drop formation
Computational analysis of drop-on-demand drop formation
复制标题
按需滴形成的计算分析
DOI：
10.1063/1.2800784
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发表时间：
2007-10-01
影响因子：
4.6
通讯作者：
Basaran, Osman A.
中科院分区：
文献类型：
--
作者：
Xu, Qi;Basaran, Osman A.
出于提高按需喷墨打印理论理解的愿望，进行了计算分析，以模拟不可压缩牛顿流体的液滴从一个简单的毛细管的喷嘴出口上游施加一个瞬态流率的形成。由于典型的喷墨喷嘴中的流动在部分时间期间朝向喷嘴出口，而在其他时间远离喷嘴出口，因此这里采用流入速率，该流入速率捕获基本的物理性质，并且以无量纲形式由Q =（π root We/2）sin Omega t给出，其中We是韦伯数（惯性/表面张力），Omega是频率，并且t是时间。的动态研究作为我们，欧米茄，和Ohnesorge数哦（粘性/表面张力）的函数。对于由半径为10 μ m的喷嘴形成的普通油墨，Oh = 0.1。对于这种典型的情况下，在（我们，欧米茄）-空间的相位或可操作性图的开发表明，三个制度的操作是可能的。在第一个政权，我们是低的，破碎不会发生，和液滴保持悬挂从喷嘴和经历时间周期性振荡。因此，模拟表明，如果要形成DOD液滴，则流体惯性以及因此的We必须足够大，这与直觉雅阁。足够大的We导致液滴伸长和液滴颈缩的发生，但是对于颈部的完全排空和毛细管箍缩，流动反向也是必要的。在其他两个制度，在给定的Ω，我们是大到足以导致液滴分裂。在这两种状态的第一种中，其中We（cl）< We < We（c2），DOD液滴确实形成，但具有负速度，即，它们将在破裂时移向喷嘴，这是不希望的。在第二破碎区域中，其中We > We（c2），不仅形成DOD液滴，而且它们以正速度形成。(C)2007年，美国物理学会。
Motivated by the desire to improve the theoretical understanding of drop-on-demand (DOD) ink-jet printing, a computational analysis is carried out to simulate the formation of liquid drops of incompressible Newtonian fluids from a simple capillary tube by imposing a transient flow rate upstream of the nozzle exit. Since the flow in a typical ink-jet nozzle is toward the nozzle outlet during part of the time and away from the nozzle outlet at other times, an inflow rate is adopted here that captures the essential physics and is given in dimensionless form by Q = (pi root We/2) sin Omega t, where We is the Weber number (inertial/surface tension force), Omega is the frequency, and t is time. The dynamics are studied as functions of We, Omega, and the Ohnesorge number Oh (viscous/surface tension force). For a common ink forming from a nozzle of 10 mu m radius, Oh = 0.1. For this typical case, a phase or operability diagram in (We, Omega)-space is developed that shows that three regimes of operation are possible. In the first regime, where We is low, breakup does not occur, and drops remain pendant from the nozzle and undergo time periodic oscillations. Thus, the simulations show that fluid inertia, and hence We, must be large enough if a DOD drop is to form, in accord with intuition. A sufficiently large We causes both drop elongation and onset of drop necking, but flow reversal is also necessary for the complete evacuation of the neck and capillary pinching. In the other two regimes, at a given Omega, We is large enough to cause drop breakup. In the first of these two regimes, where We(cl) < We < We(c2), DOD drops do form but have negative velocities, i.e., they would move toward the nozzle upon breakup, which is undesirable. In the second breakup regime, where We > We(c2), not only are DOD drops formed, but they do so with positive velocities. (C) 2007 American Institute of Physics.