Gas and temperature effect on the open- and closed-wake flow transition in gas atomization

Metal powder production via gas atomization of molten metals relies on inert gases, primarily nitrogen and argon, to meet the high-quality standards required in industries such as additive manufacturing, thermal spraying, or metal injection molding. Physicochemical interactions with the metal typically drive the selection of the atomizing gas. Additionally, the gas temperature T 0 is a crucial parameter in the atomization process, as it directly affects the kinetic energy of the gas jet. The transition between open- and closed-wake flow, as a gas dynamic mechanism, is assumed to be a key contributor to process efficiency. This work provides a comprehensive experimental study of underlying mechanisms with Schlieren imaging and aspiration pressure measurement for argon and nitrogen as atomizing gas. Both gases are heated up to T 0 ≈ 300 K, respectively ≈ 500 K. Experimental results show no significant differences in varied gas temperatures for nitrogen, in contrast to the argon experiments. The temperature sensitivity of argon is caused by condensation that occurs at low temperatures, resulting in non-ideal gas behavior. The transition between open- and closed-wake flow configurations occurs for one characteristic spatial jet expansion ratio provided ideal gas behavior can be assumed. The key conclusion is that for transition between open- and closed-wake flow to occur, a nozzle specific critical jet expansion ratio needs to be reached. • Argon shows a significant temperature effect due to condensation in the gas jet. • Nitrogen shows no significant temperature effect in the investigated range. • Wake transition occurs for very similar gas flow structures in the nozzle wake. • Critical expansion ratio hypothesis explains wake transition mechanism.