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.
|Original language||English (US)|
|State||Published - 2020|
|Event||14th International Conference on Liquid Atomization and Spray Systems, ICLASS 2018 - Chicago, United States|
Duration: Jul 22 2018 → Jul 26 2018
|Conference||14th International Conference on Liquid Atomization and Spray Systems, ICLASS 2018|
|Period||7/22/18 → 7/26/18|
Bibliographical noteFunding Information:
The counterflow nozzle exhibits features shared by all internal mixing designs compared to external mixing designs; these include lower atomizing air requirements and relatively lower sensitivity to liquid viscosity. However, these features seem to be significantly stronger in the counterflow design. The most significant outcome of this study is that even for large flow rates, SMD values remain at or less than 20 microns, despite using ALR values less than 0.2. The high sensitivity of the SMD to ALR shown in fig 7a suggests that much smaller values of SMD may be attained without significant increases in ALR, though this remains to be verified. The overall effect of this behavior is to yield a significantly increased efficiency, defined in terms of the surface area generated for a given power input towards air compression. Efficiency over a commercially available nozzle is increased by nearly 100%. For reasons that are not currently established, this performance trend is shown to increase as the liquid viscosity increases. The mechanism responsible for this behavior remains to be studied.
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