Electrohydrodynamic spraying characteristics of glycerol solutions in vacuum

An electrospray chamber has been fabricated to investigate experimentally the electrospray characteristics of glycerol solutions in cone jet mode in vacuum. At the same time, a freezing method has been developed to measure quantitatively size distributions of droplets in vacuum. According to measurement of corona onset voltages for various surrounding air pressures, electrospraying under vacuum is found to be more stable than at atmospheric pressure. The spray current depends on applied voltage as well as liquid flow rate while the droplet size is affected mainly by liquid flow rate. The mean droplet diameters measured by the freezing method are two to four times larger than those predicted by two representative scaling laws. Visualization of cone shapes shows that liquid cones do not have literally conical shapes but cusp shapes whose tips can emit a thinner jet and in return smaller droplets.