Laser Light-Sheet Visualization of the Spatial Evolution and Mixing of Coherent Droplet Structures

Summary

This paper presents the results of using the laser light-sheet technique to examine the spatial organization of droplets within an electrohydrodynamic spray. This technique is well suited for such sprays in that it can clearly delineate the boundaries of the spray and identify spatially segregated groups of droplets that occur within the spray. The technique further provides a means to quantify the extent of mixing between groups of droplets.

An electrohydrodynamic spray of typically 1 to 40 µm ethanol droplets was examined using this technique. Two electric field configurations were studied: normal and perturbed. The EHD fine spray generated using a standard capillary-plate configuration defined the normal case. This spray then was modified by introducing a small probe with an electrically-grounded tip into the spray. This modification defined the perturbed case. Video images of these sprays were acquired at a rate of 30 frames/s at two viewing angles: a side view and a top view. These were digitized into a personal computer using a frame grabber board and then displayed and enhanced using imaging software. The resulting images supported that the laser light-sheet visualization method can be used to qualify and quantify droplet mixing and the lateral spread of an electrohydrodynamic spray.