Characterization of a novel energy efficient atomizer employing countercurrent shear

The ability to atomize viscous liquids in an energy-efficient manner would enable significant cost-savings in combustion systems, potentially through the adoption of alternative fuels such as heavier grades or biomass-based oils. Conventional air-assist or air-blast atomizers rely on high levels of mean shear between the liquid stream and the air stream, and exhibit diminishing returns in performance as the kinetic energy of the air-stream is increased, leading to poor energy efficiency. We present a novel air-assist atomizer, which employs a counterflow configuration between the liquid and air streams, generating high levels of turbulent kinetic energy production and improving atomization. Experiments were performed with fluids of varying viscosity, from water to fluids with viscosities 40-times that of water and for flowrates from 2.3 g/s up to 4.2 g/s. The novel atomizer, named the counterflow nozzle, is an internal mixing nozzle and was compared to commercially available internal mixing air-assist nozzles designed to operate at similar flow rates. The counterflow nozzle consistently developed similar Sauter Mean Diameters (SMDs) as the commercial nozzle at all flow rates tested for water, but with the advantage of using only half the air mass flow. As the viscosity of the fluids tested increased, the counterflow nozzle developed sprays with smaller SMDs and a tighter droplet distribution as compared with the commercial nozzle, but again at half the amount of air flow rate. The significant improvement in atomization is explained on the basis of linear stability analysis of the counterflowing streams inside the nozzle.