Electrospray cooling and droplet evaporation

Abstract

Spray cooling utilises liquid-gas phase transition for highly efficient thermal dissipation. Electrospraying is a method of fluid atomisation by electrostatic means and has applications in colloidal propulsion, mass spectrometry, material production, biomedical sciences, and microcombustion. Of particular interest is electrospray cooling given its generation of monodisperse micron sized charged droplets, self-spray dispersion due to Coulomb repulsions, negation of droplet rebound and increased droplet spreading upon impact due to Coulomb attraction, and minimal energy and space requirements. Despite this, widespread application of electrospray cooling technology has yet to occur. This is in part due to the lack of knowledge of how basic electrospraying parameters interact to impact cooling performance. Most prominently, the mechanisms of heat and mass transfer at the solid-liquid interface are still an underdeveloped topic. This applies in a broader context to spray cooling, as well as electrospray cooling. This study experimentally investigates electrospray cooling and droplet evaporation on a heated substrate. High speed, high resolution infrared thermography is employed to measure the heat transfer characteristic of an impinging electrospray plume and evaporating droplet. Droplet evaporation is studied to examine the role that the triple line plays in heat transfer from an impacting spray on a heated substrate. Optical imaging and advanced analytical techniques are used the capture droplet dynamics over the course of its evaporation. An experimental set-up has been designed and built to facilitate these measurements, while purpose built code has been developed to analyse the acquired experimental data.