INTERNAL FLOWPATTERN AND MACROSCOPIC CHARACTERISTICS OF A FLASH-BOILING SPRAY ACTUATED THROUGH A TWIN-ORIFICE ATOMIZER WITH LOWINJECTION PRESSURE

摘要

This work is to investigate the internal flow pattern and macroscopic spray characteristics of 1,1,1,2-tetrafluoroethane (R134a) actuated through a twin-orifice atomizer. The geometry of the injector consists of one inlet orifice and one discharge nozzle separated by a cylindrical expansion chamber. Two inlet orifices with the diameters of 0.6 and 3.0 mm were conducted from the supply line of R134a to find the influence of the inlet orifice geometry on the flow and spray behavior. Four polymethacrylate atomizers were manufactured to study the effects of the various aspect ratios of expansion chambers and different diameters of discharge nozzles on the internal flow pattern and atomization characteristics. Here, the diameters of the discharge nozzles were 0.6 and 1.0 mm with the same aspect ratio of 10.0, and the aspect ratios of the expansion chambers were 0.5 and 1.0 with the same diameter of 13.0 mm. A low injection pressure of 0.6 MPa was used to produce a "stable" flash-boiling spray vertically in this work, and the ambient condition was atmospheric. The internal flow and spray images were recorded at various times after the start of actuation using a visualization system consisting of a high-speed digital camera and a metal halide lamp as the illumination source. Bubble growth, boiling phenomena in the expansion chamber, and external liquid atomization were observed simultaneously during the actuation. The transient continuous spray angles were measured at each case. The relationship between the internal boiling flow in the expansion chamber and external flash-boiling spray was analyzed. The most interesting observation is that the periodic bifurcations of the spray were formed by the twin-orifice injector when the inlet orifice diameter was 3.0 mm and the discharge nozzle diameter was 0.6 mm. This work provides a guide and reference for the volatile or liquefied material actuated through a twin-orifice atomizer with low injection pressure.