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In this study, the atomization characteristics of a commercial spillback hydraulic nozzle were investigated in terms of droplet size and velocity distributions. The spray was produced with a cold setup that can replicate the operating conditions of a commercial auxiliary marine boiler. The measurements were performed using a pulsating LED optical imaging system that employs a CCD camera to capture pairs of frames with a delay as short as 1μs from one another. Positions, velocity, sizes and shapes of single droplet were obtained by analysing the images. Mixtures of water and glycerol were used as model fluids to reproduce a range of physical properties comparable to those found by rheology studies for fuels used in this application. In addition to obtaining the droplet size and velocity distribution for the spray currently used in boilers, the general performance of the nozzle was examined in a series of experiments by varying three parameters: pressure drop, flow rate through the nozzle and liquid viscosity. Results include droplet size and velocity distributions in different spray regions, and a description of the influence of each varying parameter on global indexes such as the SMD.
