# Optimizing the Auxiliary Air Channels of a Vortex Atomizer by 3D Printing Using the Taguchi Method
###### Abstract  
In this study, the optimum spraying performance of a pressurized vortex atomizer using water as the working fluid was investigated experimentally by modifying the geometry of auxiliary air holes via the Taguchi method. The experimental results were also examined by CFD simulations. The four control factors of the auxiliary air holes are their numbers, areas, inclination angles, and lengths. With five levels for each control factor, an L\({}_{25}\) orthogonal table was selected. Each case of the L\({}_{25}\) orthogonal table was test repeatedly three times to obtain key average results. The auxiliary air holes were designed by a KISSliicer CAD tool and fabricated by 3D printing. The 3D printing was carried out by fused deposition of PLA with a resolution of about 30 \(\upmu\)m. In the experiments, the spraying jet patterns were recorded, and the water droplet weights were measured. By using the signal to noise ratios and the smaller-the-better quality characteristic, the effect of the control factors of the auxiliary air holes in descending order is the numbers, areas, inclination angles, and hole lengths, respectively. The optimum air hole configuration is the one with six holes, an inclination angle of 20\({}^{\circ}\), an area of 18 mm\({}^{2}\), and a length of 8 mm. The optimum condition was confirmed by a signal to noise ratio of 20.5 dB with 95% confidence interval. The resulting smaller jet opening angle is about 42\({}^{\circ}\), close to the simulated angle of 45\({}^{\circ}\). That is, by the novelty of combining 3D printing with the Taguchi method, this study obtains the optimum design with fast prototyping and relatively few experiments. a 2023 13 5898 1  
found that the discharge coefficient and spray angle are affected by the Reynolds number, flow rate, and atomizer geometry; [PERSON] et al. (2011) [5] showed that the droplets could be varied by changing the mass ratio of the air to liquid for their internally mixed atomizer; [PERSON] et al. (2015) [6] observed wave patterns in the liquid film of their air-core atomizers, whereas [PERSON] et al. (2008) [7] observed flow branching and focusing in their air-assist micro-atomizer. Additionally, [PERSON] et al. (2022) [8] developed a model to scale the liquid mass flow in gas-assisted coaxial nozzles. For geometric effects, [PERSON] et al. (2018) [9] showed that a proper location for flow spill can stabilize the atomization process. [PERSON] et al. (2014) [10] showed that the exit area of the atomizer affected the morphology of the droplets of liquid jets. [PERSON] and [PERSON] (2020) [11] studied a new mechanical atomizer with optimal geometric parameters for the swirler and a preliminary swirl stage, which was followed by a swirl chamber where air was introduced in an air-assisted atomizer. Furthermore, the geometric effect is always coupled with the atomizing pressure. For example, [PERSON] and [PERSON] (2019) [12] showed the importance of the inner shield depth and pressure to the size of the droplets. Additionally, [PERSON] et al. (2019) [13] further pointed out, both numerically and experimentally, the importance of the shaping air holes of the atomizer, in addition to the importance of pressure. [PERSON] et al. (2019) [14] revealed that enlarging the exit size could decrease the atomization efficiency in the pressure range from 0.4 to 0.8 MPa. They were able to generate droplets with a Sauter mean diameter of 5-6 \(\upmu\)m under high pressure. Alternately, [PERSON] et al. (2019) [15] studied the inductive charging effects on the droplets. Their results revealed that lower nozzle flow rates generated sprays with a higher specific charge due to a smaller Sauter mean diameter. The modeling and experimental results of [PERSON] et al. (2012) [16] indicated that the formation of hollow conical sprays resulted in large droplets and the recirculation zones with small droplets. In addition to coaxial air-assisted flows, cross flow situations have also been explored. As examples, [PERSON] et al.