Electrospraying of binary-mixture of water-alcohol*

There is still debate surrounding the electrohydrodynamic pulverization of water in a cone-jet mode in the air at atmospheric pressure. Indeed, researchers working on nanoelectrospray ionization mass spectrometry are aware that deionized water can be electrosprayed in cone-jet mode. The explanation given is that if liquids with sufficiently high surface tension are electro-atomized, corona discharges could form before the formation of the cone jet because the threshold value of the electric field required to form a Taylor cone-jet, which increases with the surface tension of the liquid-gas atmosphere, can become larger than the electrical breakdown threshold of the air. Spraying in cone-jet mode is preferred due to the generation of the mono-dispersed droplet which has applications in many fields such i.e. printing, coating, heat transfer, etc. Water electrospraying is very important for the application of heat transfer since it has the best-known thermophysical properties. Therefore, in this study, high throughput electrospraying of water is investigated utilising a binary fluid made of water and alcohol. In contrast to a straightforward nozzle, a hemispherical capped nozzle is employed to achieve a high flow rate. No cone jet mode is observed for water while a binary mixture of water-ethanol can be electrosprayed at the maximum flow rate of 90 ml/hr for the mixture of 40 % ethanol by volume in water. This can be attributed to the fact that alcohol reduces the surface tension of the water, thus water can be electrospray in the air atmosphere once surface tension is reached below a certain value.