The stability of a droplet suspended in a straight micro-channel

CFD simulations of the dynamics of a two-dimensional, incompressible, and two coupled spherical-cap water droplets suspended in a straight micro-channel, whose channel height is D, have been conducted to investigate the stability of the droplet. FLUENT with a 2-D pressure based solver is utilized in this simulation. The suspended droplet states are measured by the location of the central of mass of the droplet. We find that there is a critical volume, Vc(D), where asymmetric droplet states appear in addition to the basic symmetric states when V $>$ Vc(D). Using the CFD it is demonstrated that when V $<$ Vc(D) the symmetric droplet states have a stable mode. However, when V $>$ Vc(D) the symmetric states become unstable and asymmetric states have a stable mode. The bifurcation of asymmetric states at Vc(D) has a pitchfork nature. The simulations clarify the relationship between the linear stability results and the experimental results of the droplet behavior.