Microdroplet coalescences at microchannel junctions with different collision angles

Abstract

in Wiley Online Library (wileyonlinelibrary.com).Microdroplet coalescence mechanism is very important for the miniaturization of multiphase chemical processes with microstructured devices. Using three working systems with different physical properties, this article presents an experimental study on the fluid dynamics of microdroplet coalescence at different microchannel junctions. The critical capillary number to distinguish coalescence or noncoalescence of microdroplet is investigated and its variations with droplet size, collision angle, and physical properties are analyzed with two important parameters -the film drainage time and droplet contact time. Experimental results indicate that microdroplet coalescence can be enhanced by reducing the droplet collision angle. The differences of microdroplet coalescences in confined microchannels and free-flowing spaces are provided with the analysis of critical capillary number. A model equation is proposed to predict the critical capillary numbers in this study, which may provide valuable information for the design and development of new microstructured chemical device.

Study of flow behaviors of droplet merging and splitting in microchannels using Micro-PIV measurement

“…After about 1 ms, the liquid film was drained out and coalescence occurred. This squeeze-induced coalescence of deformed microdroplets at the T-junction was similar to that reported by Wang et al (2013b), Yang et al (2012) and Christopher et al (2009). When the front microdroplet enters the main microchannel (Fig.…”

“…Microdroplets in microgrooves are compressed by the walls of the microfluidic chip, making the liquid film difficult to be drained out than that in macro-scale flow. Many factors can have influence on the occurrence of coalescence, such as the microchannel geometry, the viscosity ratio of two-phase fluids, the diameter of microdroplets, the rotation of the microdroplet and the capillary number ( Ca ) (Wang et al 2013b; Liao and Lucas 2010). …”

“…Passive methods are generally flow-induced and based on geometry-mediated mechanisms (Christopher et al 2009; Zhou et al 2015; Wang et al 2014). It has been demonstrated that droplet merging can be achieved by using flow resistance structures (Xu et al 2011; Tan et al 2004), micro column structures (Niu et al 2008), T-junction structures (Christopher et al 2009; Yang et al 2012), Y-junction structures (Wang et al 2013b), cross-shaped junctions (Wang et al 2013a), and so on. Meanwhile, microdroplet splitting can be obtained at precise locations such as 3D crossing microstructures (Chen et al 2012, 2016), T-shaped junction (Tan et al 2004; Yoon et al 2013; Hoang et al 2013; Link et al 2004), branching channels (Moritani et al 2011; Zhou et al 2015), and artificial obstacle inside channels (Chung et al 2010; Li et al 2014; Protière et al 2010).…”

“…However, there are only a few qualitative visualization studies on the velocity vector field of microdroplets during merging and splitting using micro-PIV (Wang et al 2013a, b; Liu et al 2015; Jin and Yoo 2012). Systematic quantitative studies for better understanding of the fluid dynamic characteristics of microdroplet merging and splitting are needed.…”

Advances in Microfluidics Applied to Single Cell Operation

“…Fusion occurs when the interface of two adjacent droplets was instable. The velocity, the properties of fluid and the collision angle of droplets have big influence on the droplets fusion …”