Spray Transport Fundamentals

Abstract

This chapter will present insights into the spray evolution and spray transport process during melt atomization and sprays based on multiphase flow analysis with momentum and energy transfer. Spray processes typically involve the liquid atomization stage and the multiphase phase flow within the spray. In the present example the spray consists of a two-phase flow with melt droplets and gas (metal melt atomization for powder production or spray forming) or even a three-phase flow of solid particles, melt droplets and gas (spray processing of metal-matrix-composites). The evolution of the spray depends on a series of physical phenomena involved initiated by bulk liquid disintegration (i.e. primary atomization), breakup of primary fragments like ligaments and droplets (i.e. secondary atomization), momentum and heat exchange between gas and melt, droplet solidification, droplet-droplet or particle-droplet collisions. The gas flow dynamics, especially in a twin-fluid atomization process, is an important topic here. The physics of atomization of liquid metal into dispersed phases and subsequent spray of those dispersed phases is mainly governed by very high and rapid momentum and heat transfer between the high speed atomization gas phase and the molten metal stream. A detailed introduction is given to the fundamentals of liquid atomization, in which the up-to-date understandings in liquid jet/sheet disintegration mechanism and droplet breakup mechanism, as well as the recent progress in melt atomization and spray process modelling, are presented. The research progress on the kinetic dynamics and thermal dynamics of dispersed phases in spray process, as well as the conclusions from the investigations of droplet-droplet or particle-droplet collision process will be given. At last, a multiscale description of particle-droplet interactions in spray processing of metal-matrix-composite (MMC) particles is described, and thereby the optimized operation condition and spray configuration for the maximum production efficiency of MMC particles in spray processes can be derived.