3. Two Fluid Atomization Fundamentals

In this chapter we review the major types of atomization process configurations: free-fall gas atomization with an unconfined melt stream and close-coupled gas atomization with controlled melt introduction to an energetic gas flow. Studies will be reported of several types of devices, termed atomization nozzles, which are used to perform two-fluid atomization processes that involve the disintegration of a molten metal by interaction with a high velocity atomization gas. The resulting atomization process is a complex physical phenomena consisting of stages that start with melt stream pre-filming and distribution to the primary atomization zone, where melt sheets or ligaments form and initial droplet breakup (primary atomization) occurs by the interaction of a high density, hot melt with a high velocity (high kinetic energy, but low temperature) atomization gas, typically. Primary atomization is followed in the near-field region by secondary breakup, if a high enough gas velocity and sufficient mismatch velocity with the melt fragments are maintained to cause significant production of further droplets. Thus, the atomization processes described in this chapter essentially involve momentum and heat exchange between gas and melt, while other chapters will discuss the subsequent processes of droplet solidification, droplet-droplet or particle-droplet collisions and other spray phenomena that are important to spray deposition. Primarily, this chapter will deal with our state of understanding of melt breakup physics and the various types of gas atomization nozzles that can be used to generate an atomized molten metal spray.