MODELING OF DROPLET GAS INTERACTIONS IN SPRAY ATOMIZATION OF TA-2.5W ALLOY

In the present paper, the droplet-gas interactions that are present du ring spray atomization of a Ta-2.5W alloy using N-2 gas are numericall y investigated. A simple two-dimensional (2D) now model and a lumped p arameter formulation based on the modified Newton's law of cooling are developed to simulate the flow and heat transfer phenomena, including rapid solidification of droplets in the spray cone. The 2D distributi on of droplet velocity, temperature, cooling rate and solid fraction i s calculated. The microstructural characteristics of solidified partic les and as-deposited materials are discussed briefly. The effect of dr oplet size on the 2D distribution of now, thermal and solidification h istories is also addressed. The numerical results demonstrate that, at any axial distance, the droplet velocity, temperature, cooling rate a nd solidification rate all exhibit a maximum at the spray axis, and de crease 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 ax ial distance, a small droplet exhibits a wider radical distribution. H ence, coarse droplets constitute the core whereas the periphery of the spray cone is populated by fine droplets. Accordingly, the microstruc ture of spray deposited materials is predicted to be fine in the edges of the deposits as a result of high cooling rates associated with sma ll droplets. These results are in qualitative agreement with available findings.