10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Stability and Control of the Electrospray Cone-Jet Mode
Gabriel Garcia-Soriano, Santiago Martin, Jose L Castillo, PEDRO L GARCIA-YBARRA, Universidad Nacional de Educacion a Distancia - UNED
Abstract Number: 1369 Working Group: Materials Synthesis
Abstract Electrospraying is a valuable technique to prepare nanostructured layers by aerosolization and deposition of nanoparticles on a collector. This method has been used for the formation of catalytic coatings with a very large active surface to be used as PEM fuel cell electrodes. The sprayed liquids are inks prepared by stirring solutions of catalytic nanoparticles in alcohols that are impelled to the electrospray nozzle by a syringe pump at a constant flow rate. To get a high degree of homogeneity in the coating, the spraying is done in the cone-jet mode which guaranties the emission of a continuous jet of monodisperse droplets that, after the alcohol evaporation stage, leads finally to an aerosol of solid charged nanoparticles driven by the electric field towards the collector. The bottle neck of the method is the small yield of the electrospray, which compel to work with the maximum allowed flow rate to minimize the deposition time. However, large values of the flow rate render unstable the cone-jet mode when the voltage difference between the nozzle and the collector surpass the borders of the “stability island”. This region has a wedge shape that shrinks for large flow rates where the cone-jet mode is easily destabilized leading to either a multijet mode or an oscillating mode.
A control system has been developed to retain the electrospray in the cone-jet mode. The system is based on a continuous measurement of the current at the nozzle due to the emission of charged droplets. The determination of the cone-jet stability borders is cumbersome due to the hysteresis displayed by the electrospray in the transition between this mode to and from the other working regimes. The boundaries of the stability island of an ethanol electrospray have been characterized and the emitted current measured in the different regimes with high temporal resolution. The current shows abrupt jumps when the electrospray mode changes. This characterization has been used to set up a proportional-integral-derivative PID control system to maintain the electrospray in the cone-jet mode for long periods of operation.