Temporally-resolved inkjet drop impaction on surfaces

Impaction on smooth solid substrates of drops formed by the drop-on-demand (DOD) method was investigated over a wide range of impaction speeds (U-0 = 2.21-12.2 m/s), surface contact angles (theta = 6-107 degrees), and drop diameters (D-0 = 40.8-50.5 mu m). The experimental results were compared with several existing equations for predicting maximum spreading. The dimensionless time to reach maximum spreading ratio, scaled by D-0/U-0, ranged from 0.6 to 2.99, depending on Weber number and contact angle. Micron and millimeter drop impactions were compared, and the results indicate that scaling based on three dimensionless numbers (We, Re or Oh, and cos 0) is valid, but spreading ratios of millimeter drops are usually slightly larger during the whole process. The difference is ascribed mainly to the effect of gravity. (c) 2007 American Institute of Chemical Engineers.