Dripping-Jetting Transition Of Liquid Stream From Plate-Type Micro-Orifice Affected By Wetting And Dewetting

The liquid stream from an orifice typically undergoes a transition process from dripping to jetting under increased pressure. The dripping-jetting (D-J) transition performance from a thin-walled tube or an orifice with a wide diameter has been well studied, where the triple contact line of the stream is pinned on the edge of the orifice and the flow behaviors are analyzed accordingly with a precondition of the fixed contact line. The D-J transition of the liquid stream from plate-type micro-orifices was investigated in our study of droplet generation for extreme ultraviolet source and wafer cleaning. The triple contact line of the stream keeps moving as pressure changes as a result of the liquid wetting and dewetting around the micro-orifice. The transition from dripping to jetting involves three processes: wetting to generate pendant droplet and dripping, jetting from pendant droplet, and pendant droplet dewetting to form jetting directly. The aforementioned performance is different from boundary-pinned conditions. To reveal the transition characteristic, critical pressure causing the D-J transition under different wetting conditions was determined. The process of wetting to generate pendant droplet and dripping, and the effects of the contact angle and the pressure difference were formulated. Analysis of the mechanism causing jetting from the pendant droplet was implemented by combining a model formulating the jet ejecting outside the droplet and numerical simulation of the stream inside the pendant droplet. Finally, the normalized model was built to illustrate the critical pressure of D-J transition concerning the triple contact line diameter.