In this study, we examine the enhanced atomization of viscous liquids by a novel two-fluid atomizer. The nozzle employs a counter-current flow configuration, in which the atomizing gas and liquid are directed counter to each other, establishing a two-hose mixing layer before exiting the nozzle as a spray. Such a configuration is expected to establish self-sustained oscillations in the flow that produces a dominant disturbance that determines gas bubble diameter, in turn determining the liquid filaments and final droplets exiting the nozzle. Detailed measurements of droplet size distribution were performed using a shadow graphic technique using a 532 nm pulsed Nd:YaG laser and a 14 MP digital camera, with a measurement accuracy of under 1 micron. The performance of this nozzle is compared to the ‘flow-blurring’ nozzle studied by other investigators for four glycerol-water mixtures of viscosity ranging from 1 to 200 mPa.  It is found that the counter-flow nozzle produces similar droplet diameters as the flow-blurring nozzle over the range of viscosities, albeit with a reduction in the required mass flow rate of atomizing gas, with reductions in the range of 50%-200%.  Simulations are carried out using Eulerian-Eulerian Volume of Fluid (VOF) approach for the counter-flow nozzle and flow-blurring nozzle over the same range of viscosities. Gas and liquid are considered as compressible fluids with perfect gas and perfect fluid equations of state, respectively. Schiller Naumann interphase drag model is used to capture the dynamics of gas bubbles in liquid, and surface tension is considered. The simulation results are validated by the measurements of droplet size distribution, and then are used to reveal the detailed process of self-sustained flow oscillations and the physical mechanism to generate liquid filaments and final droplets.


Atomization of High Viscosity Liquids Using a Two-Fluid Counterflow Nozzle: Experiments and Modeling

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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