The main purpose of the present work is to unveil the atomization mechanism and internal flow patterns of gas/liquid mixtures flowing through Y-jet twin-fluid atomizers. Basically, the internal and external flows were visualized and examined, and the drop sizes and the flow rates of liquid and gas were measured. Injection pressures of the liquid and gas, mixing port length of the atomizers, and the liquid viscosity were taken as the parameters.
To study the flow pattern and the related disintegration mechanism, the internal flow within the mixing port and the external flow were visualized simultaneously. Drop sizes were also measured to examine the spray performance. The liquid/air momentum ratio was considered to be the appropriate parameter to describe both the internal flow and spray characteristics. A comprehensive physical model describing the atomization process is proposed; the process consists of direct collision, drop entrainment and deposition, and liquid film disintegration modes. The validity of the model was also checked with the drop size distribution data. It was confirmed that the trend of the circumferential film thickness variation within the mixing port coincides with the variation of the spatial distribution of spray drops.
The air flow rate was slightly affected by the change of the mixing port length. However, the liquid flow rate was relatively more susceptible to the change of the mixing port length. With the shorter mixing port length, drop sizes are spatially more even, and the cross-sectional averaged drop size becomes smaller. Viscosity of the liquid plays only a minor role in forming the internal flow pattern and the shape of the spatial distribution of drops outside the atomizers. However, the drop sizes were dramatically increased with the higher liquid viscosity.
Several useful correlations for the design of the Y-jet atomizers were deduced from the experimental results. The discharge coefficient through the liquid port was successfully correlated with the volumetric quality at the mixing point. The air flow rate through the gas port can be predicted by using the polytropic expansion flow correlation based on the compressible flow theory. The mixing point pressure was expressed in terms of the air/liquid flow rate and the aspect ratio of mixing port. A basic correlation form for the cross-sectional averaged drop size based on the physical model for the atomization mechanism was considered, and then a tentative correlation was given in terms of the mean gas density within the mixing port, Weber number and a flow parameter F reflecting the variation of liquid film thickness inside the mixing port.