Initiation of air core in a simplex nozzle and the effects of operating and geometrical parameters on its shape and size

Experimental investigations have been carried out to recognize the phenomenon of initiation of air core in a simplex type swirl spray pressure nozzle and to determine the influences of nozzle geometry and nozzle flow on the size of the fully developed air core. It has been recognized that below a certain Reynolds number at inlet to the nozzle, liquid flows full through the nozzle without the formation of an air core, while, above a certain Reynolds number at inlet to the nozzle, the formation of a fully developed central air core of cylindrical shape takes place in the nozzle. A transition flow with the development of a central air core takes place within the nozzle in between the two limiting inlet Reynolds numbers. These two limiting Reynolds numbers Re L1 and Re L2 are found to be an inverse function of the ratio of orifice to swirl chamber diameter ( D o/ D s) and a direct function of the ratio of tangential entry port to swirl chamber diameter ( D p/ D s). It has been observed that the fully developed central air core is cylindrical in shape with a sudden bulging in diameter at the entrance to the orifice. The air core diameter in both converging and orifice sections of the nozzle increases with an increase in the inlet Reynolds number ( Re) at its lower range, while it becomes independent with Re at its higher range. The ratio of air core to orifice diameter (da 2/ D o) increases with an increase in D o/ D s or swirl chamber cone angle ( α), and a decrease in D p/ D s or L o/ D s (the ratio of the orifice length to swirl chamber diameter). The ratio of air core diameter in the orifice to air core diameter in the swirl chamber of the nozzle (da 2/da 1) is an inverse function of D o/ D s but a direct function of D p/ D s. Empirical relations of the ratios of air core to orifice diameter, da 1/ D o and da 2/ D o, with the pertinent dimensionless controlling parameters have been established.