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Atomization and Sprays
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ISSN Print: 1044-5110
ISSN Online: 1936-2684

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Atomization and Sprays

DOI: 10.1615/AtomizSpr.2012005269
pages 259-274

NUMERICAL STUDIES OF THE FLOW STRUCTURE IN THE FINAL DISCHARGE ORIFICE OF EFFERVESCENT ATOMIZER

Baoren Li
FESTO Pneumatic Center, Huazhong University of Science and Technology, Wuhan 430074, China
Lingyong Pan
FESTO Pneumatic Center, Huazhong University of Science and Technology, Wuhan 430074, China
Gang Yang
FESTO Pneumatic Center, Huazhong University of Science and Technology, Wuhan 430074, China

ABSTRACT

In order to investigate and describe the influence of liquid physical properties and internal geometry on the two-phase flow structure in the final discharge orifice of an effervescent atomizer, numerical simulations were carried out by means of the Volume of Fluid technique considering a two-dimensional axis-symmetric domain at low gas-to-liquid mass flow ratios (GLR). Both Newtonian and non-Newtonian liquids with different viscosities and surface tension were employed in the simulation. Several circle final discharge orifices with diameters of 0.41,1.0 and 1.5 mm were tested. In all test cases, the length/diameter ratio was equal to 5 with GLR of 0.08%. The variations in bubble sizes, bubble generation characteristics and liquid film thickness in the final discharge orifice with change in fluid type and orifice diameters were examined. It was found that the slug flow structure was obtained in the final discharge orifice under different liquid types and orifice diameters. However, larger orifice diameters impart higher bubble generation rate and bigger bubbles. The effect of liquid viscosity on the two-phase flow structure in the final discharge orifice was studied in detail. The results show that liquid viscosity plays an important parameter influencing the bubble characteristics and film thickness inside the final discharge orifice. The liquid film thickness increased appreciably when the liquid viscosity increased from 0.02 to 0.08 N·s/m2. The influence of liquid surface tension on the two-phase flow structure was also studied, ranging from 0.0228 to 0.072 N/m. The simulation results were compared with the experimental studies available in the literature. These observations suggest that the bubble generation rate inside the final discharge orifice is important during effervescent spray formation.