(518d) The Liquid Film Behavior Outside a Twin-Fluid Atomizer and the Model Prediction

The forming and developing process of liquid film in the near-nozzle zone with the internal-mixing twin-fluid atomizer plays an important role in understanding the mechanism of atomization. Due to the coupling effect of inertia force and aerodynamic force, fluctuations are caused on the surface of the film and are notably enhanced by the strong mixing of gas-liquid. In this work, the liquid film behaviors during the air-water twin-fluid atomization were investigated experimentally. A laser with plane lens was employed to penetrate the focused area so that the liquid films were recorded by a high-speed CCD camera in the vertical direction. Both high pressure (gage pressure: 0.1~0.5 MPa) and low pressure (gage pressure: 1~10 kPa and 10~90 kPa) cases were conducted in order to better observe and analyze the properties of the liquid film instabilities and thickness, respectively. The results show that introduction of gas is able to accelerate the perturbation and breakup of film. Statistical analysis gives that the fluctuation frequency increases with the increase of inlet pressure or the gas to liquid mass ratio (GLR). However, the amplitude decreases with increasing the inlet pressure and increases with increasing GLR. The liquid film thickness is obviously larger than the proposed model predictions which were based on the assumption of the annular flow. So a new model was proposed based on the assumption of partial annular flow so that a better prediction of the film thickness at the nozzle outlet was proposed. The predictions give a better agreement with the experimental data.