Abstract:

The droplet generation process of the water-silicone oil system in the coaxial microchannel was studied. Under different continuous capillary number Ca_c and dispersed phase Weber number We_d, two different flow patterns, dripping flow and jet flow, were observed. Experiments examined the effects of two-phase flow, viscosity, and inner tube structure on droplet size and droplet generation frequency. The results showed that droplet size increased with the increase of dispersed phase flow rate and decrease of flow rate and viscosity of continuous phase. Additionally, with the increase of We_d, jetting occurrence was found to be easier in relatively larger capillary, which in turn generated larger droplets. The generation frequency of droplet increased fast firstly then slow down to a plateau with the increasing of Ca_c and We_d. When the hydraulic diameters of inner channel were almost same, the deviation in the generation frequency of droplet obtained from different geometries of inner channel was small at fixed Ca_c. And the generation frequency of droplet increased with the decrease in the hydraulic diameters of inner channel. Based on the obtained results, an empirical correlation was proposed to predict the droplet size with good prediction performance.

Key words: microchannels, two-phase flow, inner channel geometry, droplet formation, flow regimes

摘要：

研究了同轴微通道内水-硅油体系的液滴生成过程。在不同的连续毛细数Ca_c和分散相Weber数We_d下，观察到滴出流和喷射流两种不同的流型。实验考察了两相流量、黏度和内管结构对液滴尺寸和液滴生成频率的影响。结果表明液滴尺寸随着分散相流量增加而增大，而随着连续相流量和黏度的增加而降低。此外，随着We_d的增加，流型会从滴出流过渡到喷射流，而更大尺寸的内管会更早过渡到喷射流，从而得到更大的液滴尺寸。对于液滴生成频率，其随Ca_c和We_d的增加均呈现先快速增加后变缓的趋势。当内管通道尺寸基本相同时，不同结构的内管通道在固定Ca_c时其液滴生成频率相差不大，且随着通道尺寸的减小，液滴生成频率逐渐增加。基于实验结果，建立了液滴尺寸预测模型，预测值与实验值吻合较好。

关键词: 微通道, 两相流, 内管结构, 液滴生成, 流域