MEASUREMENTS OF GAS RECIRCULATION FLOW IN THE MELT FEEDING ZONE OF A CLOSE-COUPLED GAS ATOMIZATION NOZZLE

摘要

The uniform distribution of melt flow to the periphery of the delivery tube is one of the most critical aspects of close-coupled gas atomization to promote the maximum primary atomization effect at elevated gas velocities. Experiments have indicated that a strong gas recirculation backflow in the wake region of the melt feed tip is needed to drive the melt distribution phenomena and that the recirculation flow is sensitive to specific nozzle configurations and operating parameters. This investigation sought to determine the influences of gas jet apex angle and gas supply pressure on the strength of recirculation backflow in a discrete jet, close-coupled gas atomization nozzle. Miniature gas flow pressure probes have permitted recirculation velocity calculations using a dynamic pressure method that can be used to validate computational fluid dynamics (CFD) simulations. The results provide insight about previous experiments and guided nozzle redesign efforts, which lead to a subsequent gas atomization trial on pure Cu with N_2 gas. This experiment provided further understanding about the flow dynamics needed to enable a gas atomization process with high uniformity for atomization model verification and for highly selective powder production.