Enhanced thin film evaporation via impinging electrospray liquid jets with entrained air streaming

Abstract

Electrospray (ES) phase change cooling is investigated as a potential approach for heat dissipation from localized hot spots. Considering evaporation of electrospray-delivered liquid as a potentially effective and desirable heat removal scheme, experiments have been performed to characterize the behavior of liquid films formed on a heated surface by way of ES impingement under different conditions. A complementary heat transfer model has been developed to understand the heat and mass transfer mechanism underlying the process and to predict system thermal performance. With the help of the predictive model, the experimental observations have been interpreted to identify the key physical phenomena that determine evaporation from electrosprayed liquid films. It was discovered that the impinging jet is not only effective in delivering liquid to the surface, but also enables thinning of the films to only a few hundred nanometers, thus significantly reducing conduction resistance across the film. Additionally, mass transfer resistance for evaporation is also reduced by two orders of magnitude compared to natural convection as a result of the surrounding air entrainment by the spray jet, permitting significantly higher evaporation rates and heat removal than would occur in quiescent air. In summary, ES cooling is demonstrated to be uniquely capable of both liquid and gas phase heat/mass transfer enhancement supported by the electrohydrodynamics of high momentum ES spray-jets.