Modeling of droplet-gas interactions in spray atomization of Ta-2.5W alloy

In the present paper, the droplet-gas interactions that are present during spray atomization of a Ta-2.5W alloy using N2 gas are numerically investigated. A simple two-dimensional (2D) flow model and a lumped parameter formulation based on the modified Newtonʹs law of cooling are developed to simulate the flow and heat transfer phenomena, including rapid solidification of droplets in the spray cone. The 2D distribution of droplet velocity, temperature, cooling rate and solid fraction is calculated. The microstructural characteristics of solidified particles and as-deposited materials are discussed briefly. The effect of droplet size on the 2D distribution of flow, thermal and solidification histories is also addressed. The numerical results demonstrate that, at any axial distance, the droplet velocity, temperature, cooling rate and solidification rate all exhibit a maximum at the spray axis, and decrease to a minimum at the periphery of the spray cone, except for the locations where solidification occurs. The droplets in the periphery region solidify within a shorter flight distance relative to those at the spray axis owing to longer flight time in the periphery. At any axial distance, a small droplet exhibits a wider radical distribution. Hence, coarse droplets constitute the core whereas the periphery of the spray cone is populated by fine droplets. Accordingly, the microstructure of spray deposited materials is predicted to be fine in the edges of the deposits as a result of high cooling rates associated with small droplets. These results are in qualitative agreement with available findings.