Effects of continuous phase velocity pulsations on the formation and morphology of polymer droplets in microchannels

The influence of continuous-phase velocity pulsation on the generation and morphology of polymer droplets in microchannels is studied using three-dimensional direct numerical simulation. Based on the elastoviscoplastic Saramito model and the fluid volume method, combined with the local adaptive mesh refinement technology, the droplet generation process and morphological characteristics were analyzed. The results show that elastoviscoplastic velocity pulsation promotes droplet generation, and the maximum stretching length of the dispersed phase first decreases and then increases as the pulsation frequency rises. The pulsation amplitude shortens the stretching length of the dispersed phase. Under the influence of pulsation, the droplet morphology undergoes significant changes. When droplet velocity dominates, significant axial tensile stresses appear at the head and sides of the droplet. When the continuous-phase velocity dominates, the tensile stress on the sides of the droplet decreases significantly, and the droplet length is compressed. Furthermore, under velocity pulsations of the continuous phase, the average droplet length is adjustable between 102 µm and 193 µm. The average length and width of the droplets are controlled by pulsation frequency, with little influence from the pulsation amplitude.