Novel Design in Venturi-Type Nozzle by Selective Laser Melting for Enhancement in Microbubble Generation

This study applies selective laser melting (SLM) to fabricate stainless steel 316L (SS316L) structures on the distribution plate of a Venturi-type nozzle in a pressurized dissolution microbubble generator. SLM is employed because the fabricated structures are approximately hundreds of micrometers in size, making them difficult to produce using conventional milling or other machining methods. These structures are designed to enhance cavitation and gas-liquid interaction, thereby enhancing microbubble generation. Various conditions of the SLM process are conducted, and the combination of 140 W laser power, 100 mm/s scan speed, 30 µm layer thickness, and 120 µm hatch distance achieves the highest relative density while maintaining the austenite phase of SS316L, thus being selected as the optimal SLM process parameters. Microbubble generation test are conducted under three different dissolution tank pressure conditions (0.20, 0.25, and 0.30 MPa) using nozzles with and without the SLM structures. The generated microbubbles in both nozzles ranges from 1 to 110 µm, satisfying the size conditions for microbubbles. The average microbubble size is smaller in the SLM-assisted nozzle (31.8 µm) compared with the plain nozzle (38.8 µm). Furthermore, under the dissolution tank pressure of 0.30 MPa for 30 s, the SLM-assisted nozzle generates a maximum of 52,368 microbubbles, representing approximately a 102.1% increase compared with the plain nozzle (25,907 microbubbles). These results demonstrate that incorporating SLM structures to Venturi-type nozzle effectively enhances microbubble generation, offering promising potential for applications in water treatment, biomedical processes, and chemical engineering.