In the present work, the effect of ambient gas(steam) condensation on spraying characteristics of subcooled liquid(water) discharged from swirl nozzles were studied experimentally. The operating parameters were the flow rate (injection pressure) and the temperature (degree of subcooling) of the liquid. The outline configuration of liquid sheet(breakup length and spray angle) and the breakup mode(perforation characteristics) were examined through visualization and photography, and variation of the discharge coefficient was studied as well. Local and cross-sectional area-averaged SMD of droplets were obtained using the image processing method. Finally, the simple models predicting the spray angle and the mean drop size were proposed.
The perforation breakup mode appeared dominant with condensation of ambient gas (in condensable environment) while the aerodynamic wave breakup mode without condensation (in the non-condensable environment). The discharge coefficient, breakup length and the mean drop sizes decrease in a same manner with increasing of the liquid flow rate for both with and without condensation. The number density of perforation increased with increasing of the liquid flow rate in condensable environment.
Condensation of the ambient gas gave little effect on the discharge coefficient. However, drop sizes (both the local and cross-sectional area-averaged SMD) were larger and the breakup occurred earlier in the condensable environment due to change of the breakup mode. The spray angle appeared to be narrower with condensation but only marginally, because the increase of the centrifugal force due to the higher tangential velocity of the liquid sheet was almost comparable to the pressure difference across the sheet attributed to the condensation effect.
Effects of the injection temperature on the breakup length and the number density of perforation in the sheet region turned out to be relatively insignificant in condensable environment. However, the discharge coefficient and the cross-section-averaged SMD decrease with increasing of the liquid temperature. On the contrary, the spray angle with the higher liquid temperature appears wider than with the lower liquid temperature.
The discharge coefficient could be expressed successfully as a function of the swirl Reynolds number based on the tangential velocity at the swirl chamber inlet, liquid viscosity and the effective swirl chamber radius. The film thickness at the discharge orifice was also predicted to be a function of the swirl Reynolds number. However, the spray angle was not a sole function of the swirl Reynolds number.
Simple physical models predicting the cone angle and the profile of the liquid sheet portion and the film conditions (film thickness and velocity) at the nozzle exit were introduced, which agree satisfactorily with the measured data. A breakup model based on the number density of perforation at sheet breakup could estimate the measured mean drop size within the accuracy range of ±15%.
