NUMERICAL SIMULATIONS OF NEAR-NOZZLE EXIT CHARACTERISTICS FOR AN EFFERVESCENT ATOMIZER AT LOW GAS TO LIQUID MASS FLOW RATIO

Effervescent atomization is a process in which a bulk liquid is transformed into a spray of droplets by injecting a small amount of gas into the liquid before it is ejected from the atomizer. Advantages of using effervescent atomization method include larger exit orifices to reduce clogging issues, reduced injection pressures, and lower gas to liquid mass flow ratios (GLR) as compared to pressure or air-blast atomizers [1]. Effervescent atomization has been used in a number of applications including agricultural sprays, paint sprays, combustion for lowering pollutant emissions, spray cooling for gas turbine and medical applications, waste incineration, and process industry applications. In the present work, the near nozzle exit characteristics of an air-water effervescent atomizer at gas to liquid mass flow ratio such as 0.25% are investigated numerically through two-fluid Eulerian-Eulerian ensemble averaged modeling. The two-fluid model is solved through the finite volume method. Numerical simulations are performed using the commercial computational fluid dynamics (CFD) code ANSYS FLUENT. The effects of effective (average) air bubble diameter size inside the atomizer, exit nozzle diameter, and injection pressures on the average liquid water jet width are presented. An optimal bubble size is observed for increasing the average liquid jet width which leads to enhanced jet break-up at downstream of the nozzle. The water volume fraction profiles within the sprays are also reported. The numerical results are compared with experimental visualizations and jet width measurements to further the understanding of the spray characteristics of effervescent atomization for atomizer design.