In situ monitoring of electrosprayed water microdroplets using laser and LED light attenuation technique: Comparison with ultra-high-speed camera imaging

An electrostatic spray (ES) of liquids is a simple way to generate microdroplets with a high surface-to-volume ratio. The ES generated by electrical discharges enables a fast transfer of reactive species from plasma into the liquid for an efficient generation of plasma-activated water. Here, we present a relatively simple, versatile, and cost-effective diagnostic technique for online monitoring of ES microdroplets which enables simultaneous and synchronized electrical and optical diagnostics of an electrical discharge. This technique is based on planar laser light attenuation monitored by a large area photo-detector covered by a slit. Two variants were tested and compared-one with two lasers and another with one laser and a broadband LED lamp. This technique enables estimations of the speed and size of microdroplets (down to similar to 10 mu m) and allows for monitoring the dripping frequency or studying fragmentation of microdroplets and water filaments. The ES characteristics obtained by this technique were successfully verified by ultra-high-speed camer:a imaging.