Characterization of spray atomization and heat transfer of pressure swirl nozzles

The spray characteristics and heat transfer performance of pressure swirl nozzles were experimentally investigated in an open loop system. The spray flow structure, droplet Sauter mean diameter, and droplet impingement energy were characterized at predefined axial distances and pressure drops. It was found that the spray cone produced by the pressure swirl nozzles changes from hollow cone to full cone as the axial distance increases. The droplets size initially decreases with the increasing of axial distance but subsequently increases in the investigated range of axial distance, while the droplet impinging Weber number decreases monotonously. The surface temperature distribution was found to be solely dependent on the impinging droplet flux distribution in the non-boiling regime. High surface temperature expands the impinging spray cone and finally changes the impinging droplet flux distribution when the droplets impinge on the heated surface. The effect of nozzle-to-surface distance on heat transfer performance was found to be complex and surface temperature dependent. The heat transfer coefficient was investigated to be rather insensitive to the nozzle-to-surface distance at the full cone spray regime than that in the hollow cone spray regime. An empirical model that correlates the Nusselt number to the impinging Reynolds number, non-dimensional surface temperature and nozzle-to-surface distance was developed to fit the present experimental data with an average error of 14%.

► The flow structures of two pressure swirl nozzles were experimentally investigated. ► Surface temperature distribution is solely dependent on the impinging droplet flux. ► High surface temperature expands the spray cone near the heated surface. ► Nozzle-to-surface distance has complex influences on spray cooling performance. ► A concise and useful empirical correlation was developed.