Dependence of micro-drop generation performance on dispenser geometry

In this paper, the drop generation performance, represented by the speed of generation and the attainable size range of drops, of λ-junction type micro (∼100 μm) dispensers was examined for various heights, widths and fluid injection angles quantitatively. Target range of drops was about the same size of the channel hydraulic diameter (0.8–1.2 Dh,c) that is known to be most efficient for internal mixing of different components within micro-drops. Viscosities of the disperse and continuous phases were 2.7 and 2.3 mPa s, respectively. Also, the superficial velocity range of the disperse phase was 0.002–0.128 m/s and that of the continuous phase was 0.02–0.15 m/s. Hence, the corresponding ranges of the capillary and the Reynolds numbers (based on the channel width) of the continuous phase were 0.004–0.034 and 1–32, respectively. Within the present test ranges, the drop generation performance was improved with the smaller width ratio (between the side and the main inlets), and at the aspect ratio of about 0.8 and the injection angle of about 120°. Furthermore, through the detailed observations, the geometrical similarity of the bulged part of the disperse phase was confirmed to exist between the cases with different junction dimensions (widths and height), which is an important clue for prediction of drop sizes.

► Performance of λ-junction micro-drop dispenser depends on the dispenser geometry.
► The drop dispenser performance was improved with the smaller width ratio.
► The performance was improved at the aspect ratio of about 0.8 and the 120° junction.
► Geometrical similarity during drop formation process was confirmed.