Abstract
This experimental study undertakes the measurements of droplet Sauter Mean Diameter (SMD) at different axial distances for the hollow-cone nozzle and different radial distances from the spray centreline using a laser-diffraction-based drop size analyser in order to validate atomization model. The study also investigates the influence of injection pressure and the evaluation of two exit orifice diameters on the Sauter Mean Diameter (SMD). The drop size distributions along the nozzle centreline as well as the radial drop distributions from spray centreline are also evaluated. To enhance the physics of liquid sheet instability and liquid film breakup mechanisms, visualization of liquid film breakup as a function of injection pressure was carried out. The results show that mean droplet size (SMD) increases in the axial distance on the spray centreline but decreases with an increasing injection pressure on the spray centreline. It was observed that larger sized drops occupy the spray periphery compared to those occupying the spray core. For the nozzle exit orifice diameters of 3.5 mm and 1.5 mm, the results show that the small nozzle exhibits smaller SMDs than the bigger nozzle and the break-up lengths are different for the two nozzles. The drop size distributions at radial positions showed an increase in droplet formation through the spray downstream distances and become more uniform. The visualisation of the spray was carried out using high-speed camera and it was noted that a well-defined hollow-cone spray was captured and that the spray angle increases with the injection pressure but reduces with the liquid film length.
Highlights
The spray characteristics are usually measured using a Malvern Spraytec which is a non-intrusive, laserdiffraction-based drop analyser designed to continuously measure drop sizes and distribution information for continuous sprays
This experimental study undertakes the measurements of the droplet Sauter Mean Diameter (SMD) at different axial distances for the hollow-cone nozzle and different radial distances from the spray centreline using a laserdiffraction-based drop size analyser (Malvern Spraytec) and investigates the influence of injection pressure on the Sauter Mean Diameter (SMD)
It is observed that an increase in the injection pressure of liquid leads to a decrease in SMDs on the spray centreline
Summary
The spray characteristics are usually measured using a Malvern Spraytec which is a non-intrusive, laserdiffraction-based drop analyser designed to continuously measure drop sizes and distribution information for continuous sprays. For the nozzle size and the liquid used in the experiments of Lefebvre [6], 50 mm was the best minimum axial position beyond which the results were consistent and below which no meaningful information was obtained for mean drop size and distribution This agrees with the downstream distance used by Emekwuru [6]. Dombrowski and Hasson [13], Wang and Lefebvre [9] indicated that the motion in the swirl chamber is complex and the mechanisms of flow within the chamber and the resultant spray outside are not fully understood and further research needs to be conducted on this atomizer This unsatisfactory situation is due to several causes such as the great complexity of the atomisation process, differences in the design, size, and operating conditions of the nozzles tested and the inaccuracies and limitations associated with drop-size measurement techniques [3]
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