DEVELOPMENT OF A MICRO-CHANNEL BASED ROTARY ATOMIZER AND ITS SPRAY CHARACTERIZATION

A novel micro-channel based rotary (MCR) atomizer has been developed, which produces spiralling micro-jets leading to the formation of a well-dispersed fine spray. A co-swirl air stream envelops the liquid jets to aid in the process of atomization. Initially, the jet break-up process is studied using high speed shadowgraphy. The liquid jets deform into elliptical and eventually sheet-type cross-sections at higher rotational speeds, due to air drag. Also, a hydrodynamic instability develops in the form of wavelets consisting of bag-like surfaces pinned between thick crests. At higher rotational speeds or air flow rates, the wavelets break-down to form small droplets. Subsequently, secondary spray atomization characteristics of droplets due to interaction with air stream have been investigated using Phase Doppler Particle Analyzer. At axial distances of about 5 nozzle diameters, a hollow cone spray is observed, consisting of relatively larger droplets formed during jet break-up. The region close to the spray axis consists of smaller droplets entrained by the recirculatory air flow. At higher swirl, the recirculation zone widens radially and as a result, peak droplet velocities and droplet sizes shift away from the axis. At an axial distance of about 10 nozzle diameters, the droplet sizes and droplet number densities become more uniform spatially, due to competing droplet coalescence and break-up phenomena. The present novel MCR atomizer provides a nearly uniform fine spray, for a range of flow conditions.