Investigation of droplet collisions for solutions with different solids content
Investigation of droplet collisions for solutions with different solids content
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DOI：
10.1007/s00348-012-1440-z
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发表时间：
2013-01
影响因子：
2.4
通讯作者：
M. Kuschel;M. Sommerfeld
中科院分区：
文献类型：
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作者：
M. Kuschel;M. Sommerfeld
研究了高粘度聚合物溶液的液滴碰撞行为和碰撞结果。为此，由压电液滴发生器产生的两个液滴链以一定角度彼此相对，以便各个液滴对发生碰撞。为了记录碰撞事件，使用了一台双图像和一台高速 CCD 摄像机。一台摄像机垂直于碰撞平面放置，记录碰撞结果，第二台摄像机平行于碰撞平面对齐，以确保液滴链恰好位于一个平面上。开发了一种与扩展粒子跟踪测速算法相结合的跟踪液滴的新方法。使用时间分辨系列图片来分析液滴碰撞的动力学。三种不同的水溶性物质是不同分子量（K17、K30）的蔗糖和1-乙烯基-2-吡咯烷酮（PVP）。溶剂是软化水。固体含量范围为 20 至 60%、5 至 25% 和 5 至 35%，动态粘度范围为 2-60 mPa s。收集不同对碰撞角度和韦伯数的结果，以便建立通用碰撞图来表征结果。在这里，研究了相同尺寸液滴 (Δ = 1) 0.5 至 4 m/s 之间的相对速度以及 0 至 1 区间内的冲击参数。此外，还将以 K30 为例讨论卫星形成。与主要针对低粘性液滴导出的不同作者的常见模型（Ashgriz 和 Poo，J Fluid Mech 221：183–204，1990；Estrade 等人，Int J Heat Fluid Flow 20：486–491，1999）的比较表明，其有效性的上限由 Ohnesorge 数 ofOh= 0.115 和毛细管数给出。钙 = 0.577。对于这些无量纲参数的较高值以及因此较高的动态粘度，这些模型无法正确预测碰撞场景之间的边界。 Jiang等人提出的模型。 (J Fluid Mech 234:171–190, 1992)，其中包括粘性耗散，能够预测较高粘度的聚结和拉伸分离之间的边界（即 Oh > 0.115 和 Ca > 0.577）。然而，对于不同的解属性，模型常数并不相同。总之，由于表面张力和粘度之间的相对重要性，碰撞外观发生了变化。
The collision behaviour of droplets and the collision outcome are investigated for high viscous polymer solutions. For that purpose, two droplet chains produced by piezoelectric droplet generators are directed towards each other at a certain angle so that individual droplet pairs collide. For recording the collision event, one double-image and one high-speed CCD camera were used. One camera is positioned perpendicular to the collision plane recording the outcome of the collision, and the second camera is aligned parallel to the collision plane to assure that the droplet chains are exactly in one plane. A new approach for tracking droplets in combination with an extended particle tracking velocimetry algorithm has been developed. Time-resolved series of pictures were used to analyse the dynamics of droplet collisions. The three different water soluble substances were saccharose and 1-Ethenyl-2-pyrrolidone (PVP) with different molecular weights (K17, K30). The solvent was demineralised water. The solids contents ranged from 20 to 60 %, 5 to 25 % and 5 to 35 %, yielding dynamic viscosities in the range of 2–60 mPa s. Results were collected for different pairs of impact angles and Weber numbers in order to establish common collision maps for characterising the outcomes. Here, relative velocities between 0.5 and 4 m/s and impact parameters in the interval from 0 to 1 for equal-sized droplets (Δ = 1) have been investigated. Additionally, satellite formation will be discussed exemplarily for K30. A comparison with common models of different authors (Ashgriz and Poo in J Fluid Mech 221:183–204, 1990; Estrade et al. in Int J Heat Fluid Flow 20:486–491, 1999) mainly derived for low viscous droplets revealed that the upper limit of their validity is given by an Ohnesorge number ofOh= 0.115 and a capillary number ofCa= 0.577. For higher values of these non-dimensional parameters and hence higher dynamic viscosities, these models are unable to predict correctly the boundaries between collision scenarios. The model proposed by Jiang et al. (J Fluid Mech 234:171–190, 1992), which includes viscous dissipation, is able to predict the boundary between coalescence and stretching separation for higher viscosities (i.e.Oh> 0.115 andCa> 0.577). However, the model constants are not identical for different solution properties. As a conclusion, an alteration of the collision appearance takes place because of the relative importance between surface tension and viscosity.