Abstract: The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous phase. The flow pattern and its morphological changes have a significant effect on the atomization, but the influence of different parameters on the morphological change of the flow pattern remains unclear. The flow focusing pattern and morphological changes in the two-phase flow inside the nozzle were simulated numerically, based on the volume of fluid method. The results demonstrate that the ratio of the nozzle-to-capillary distance and capillary diameter, the gas-liquid velocity ratio, and capillary diameter have significant effects on the flow pattern. When the ratio of the nozzle-to-capillary distance H and capillary diameter D increases, or the capillary diameter D increases, the flow pattern tends to transform into a laminar form; however, when the gas-liquid velocity ratio V increases, the flow pattern tends to transform into a turbulence form. Furthermore, we define the cone-shaped expansion rate, cone-shaped focusing rate, and cone angle in order to study the morphological changes in the cone shape inside the nozzle. The results indicate that the morphological change of the cone shape and flow pattern transformation is interrelated. When the cone shape tends to be unstable, the flow pattern changes towards flow blurring, whereas, a stable cone indicates that the flow tends to exhibit a droplet pattern.

Key words: Flow focusing, Pattern transformation, Morphological changes, Numerical simulation

摘要： The flow focusing nozzle is a new type of nozzle that performs effective atomization of the discrete phase by means of high-speed motion of the continuous phase. The flow pattern and its morphological changes have a significant effect on the atomization, but the influence of different parameters on the morphological change of the flow pattern remains unclear. The flow focusing pattern and morphological changes in the two-phase flow inside the nozzle were simulated numerically, based on the volume of fluid method. The results demonstrate that the ratio of the nozzle-to-capillary distance and capillary diameter, the gas-liquid velocity ratio, and capillary diameter have significant effects on the flow pattern. When the ratio of the nozzle-to-capillary distance H and capillary diameter D increases, or the capillary diameter D increases, the flow pattern tends to transform into a laminar form; however, when the gas-liquid velocity ratio V increases, the flow pattern tends to transform into a turbulence form. Furthermore, we define the cone-shaped expansion rate, cone-shaped focusing rate, and cone angle in order to study the morphological changes in the cone shape inside the nozzle. The results indicate that the morphological change of the cone shape and flow pattern transformation is interrelated. When the cone shape tends to be unstable, the flow pattern changes towards flow blurring, whereas, a stable cone indicates that the flow tends to exhibit a droplet pattern.

关键词: Flow focusing, Pattern transformation, Morphological changes, Numerical simulation