Breakup of an isolated surface-adhering water droplet by an impinging jet flow

The study explored the depinning and breakup of a single surface-mounted droplet exposed to an impinging slot jet flow. Distilled water droplets of 50, 100, 200, 300, 400, 500, and 600 μl were tested on an anodized aluminum substrate in the impinging slot jet facility whose velocity was ramped from zero to 20 m/s at a range of accelerations. The breakup process comprised three distinctive consecutive stages: depinning, necking, and breakup. An aggregate analysis of the data from the present investigation and the results of previous studies is used to deduce that the Weber number at which depinning occurs was roughly constant for all tested conditions, whereas the Weber number at breakup followed a power-law relationship with the Ohnesorge number. The observed power law relation for surface-mounted droplets is similar to the trend reported earlier for critical conditions demarcating breakup regimes for free-falling droplets. During breakup, it was observed that larger originating droplets shed larger percentages of their volumes into secondary droplets, with higher flow accelerations exacerbating this effect. The majority of the formed secondary droplets had a higher critical depinning Weber number compared to the critical breakup Weber number. Consequently, for applications requiring the complete removal of surface-deposited droplets, it is beneficial to utilize shear flows at lower accelerations and maximum Weber numbers below critical breakup conditions.