Energy considerations in spraying process of a spill-return pressure-swirl atomizer

Abstract

The work focuses on energy conversion during the internal flow, discharge and formation of the spray from a pressure-swirl (PS) atomizer in the simplex as well as spill-return mode. Individual energy forms are described in general and assessed experimentally for a particular PS atomizer and light heating oil as a medium. The PS spray was observed at various loads to investigate the liquid breakup process and the spray characteristics. Spatially resolved diameters and droplet velocities, measured by means of phase-Doppler anemometry, served for estimation of the energy characteristics in the PS spray. The input energy given by the potential energy of the supplied liquid partially converts into the kinetic energy (KE) in the swirling ports with hydraulic loss in per cent scale. Most of the pressure drop is associated with rotational motion in the swirl chamber with total conversion efficiency at the exit orifice 58%. The rest of the input energy ends up as friction loss, leaving room for improvement. The overall value (ID32) of the Sauter mean diameter of droplets in the spray, D32, varies with pressure drop dpl powered to –0.1. The radial profiles of D32 widen with the increase in spill/feed ratio (SFR), but the ID32 remain almost constant within the studied SFR range. The spray KE at closed spill line covers the droplet KE (21–26%) and that of entrained air (10–13%), both moderately varying with dpl. The specific KEs of both the liquid and air markedly drop down with the spill line opening. Atomization efficiency is less than 0.3% for the studied range of operation regimes and depends on dpl and SFR. Our results confirm low power demand of simplex PS atomizers, with extra energy consumption in spill mode. Several recommendations are given for PS atomizer innovations and development of new, more efficient, designs meeting more stringent environmental requirements.The work focuses on energy conversion during the internal flow, discharge and formation of the spray from a pressure-swirl (PS) atomizer in the simplex as well as spill-return mode. Individual energy forms are described in general and assessed experimentally for a particular PS atomizer and light heating oil as a medium. The PS spray was observed at various loads to investigate the liquid breakup process and the spray characteristics. Spatially resolved diameters and droplet velocities, measured by means of phase-Doppler anemometry, served for estimation of the energy characteristics in the PS spray. The input energy given by the potential energy of the supplied liquid partially converts into the kinetic energy (KE) in the swirling ports with hydraulic loss in per cent scale. Most of the pressure drop is associated with rotational motion in the swirl chamber with total conversion efficiency at the exit orifice 58%. The rest of the input energy ends up as friction loss, leaving room for improvement. The overall value (ID32) of the Sauter mean diameter of droplets in the spray, D32, varies with pressure drop dpl powered to –0.1. The radial profiles of D32 widen with the increase in spill/feed ratio (SFR), but the ID32 remain almost constant within the studied SFR range. The spray KE at closed spill line covers the droplet KE (21–26%) and that of entrained air (10–13%), both moderately varying with dpl. The specific KEs of both the liquid and air markedly drop down with the spill line opening. Atomization efficiency is less than 0.3% for the studied range of operation regimes and depends on dpl and SFR. Our results confirm low power demand of simplex PS atomizers, with extra energy consumption in spill mode. Several recommendations are given for PS atomizer innovations and development of new, more efficient, designs meeting more stringent environmental requirements.