Effect of liquid viscosity, surface tension and nozzle size on atomization in two-phase nozzles

The main objectives of this study were to compare global Sauter Mean Diameter (SMDgb) produced from sprays of different viscosities, surface tension and sizes of small-scale fluid coker (FC) nozzles. The final objective was to establish a SMDgb correlation as a function of nozzle size, viscosity, surface tension and flow conditions. This study was performed as first step in understanding the atomization behaviour of FC nozzles in situ.;Compressed air was used as the gas phase, the liquids were water, canola oil and glycerine solution. Liquid viscosities were varied from 1 mPa-s to 67 mPa-s, and surface tensions were varied from 25 mN/m to 70 mN/m. All fluid properties were at 21°C. The liquid flow rates were varied from 95g/s to 195 g/s, and the Gas-to-Liquid-Ratio (GLR), by mass, was fixed at 1%, similar to the commercial FC nozzles. Operating conditions with 2% GLR were also studied. Fluid mixing pressures in the test were between 516 kPa to 998 kPa. The nozzles used were a one-quarter and one third scale nozzle, which were geometrically similar to a commercial FC nozzle. Dimensional analysis was used to determine the flow conditions required to operate the nozzles at similar flow conditions. The SMD within the spray was measured using a Dantec 2-D Particle Dynamics Analyzer (PDA). Measurements were performed at axial distances of 100, 202 and 405 mm from the nozzle exit and within spray widths of -50 mm to 50 mm in the horizontal plane.;The results showed that drop size increases significantly between 34 to 64% with liquid viscosity. Surface tension effects on drop size can be negligible at 1% GLR and axial position within 32 D of the nozzle exit. The other results showed an increase (between 15 and 25%) in drop size with a decrease in surface tension. The SMDgb increased by up to 31% with the bigger nozzle. Finally, the SMDgb correlation estimated drop size within 17% maximum deviation. Results from this study provide a comprehensive means of improving the design of two-phase fluid coker nozzles.