Classification and Prediction of Dripping Drop Size for a Wide Range of Nozzles by Wetting Diameter

In this study, dripping drops of water and glycerol/water mixtures from 83 nozzles (in the range of 0.065 mm ≤ Do ≤ 40 mm and 0.043 mm ≤ Di ≤ 35 mm, where Do and Di are the outer and inner diameters, respectively) were systematically investigated for four fluids, three wettable nozzle materials, and various liquid feeding rates under the simple dripping mode condition in an ambient gas, that is, air. It is important to point out that no single characteristic length scale mentioned in the literature can be used to satisfactorily predict all experimental data. A new characteristic parameter, that is, the wetting diameter (Dw), has been introduced, and its usefulness in predicting the drop size by a simple relation in the whole nozzle range is shown for the first time. The critical wetting diameter (Dc), which is related to the wettability (or advancing contact angle) of the dripping liquid and the nozzle material, is theoretically derived, and its dimensionless value (Dc*), normalized by the capillary lengt...