Design of a three-nozzle for air spraying based on jet interference effect and numerical study of spraying process

Due to the problems of many round-trip time and low spraying efficiency when using single-nozzle, a three-nozzle structure is studied in this paper. The spraying process is numerically simulated by the method of computational fluid dynamics. The discrete phase model is used to predict the trajectory of droplets. The interference flow field is formed due to the entrainment of jet. Paint droplets are transported to the target under the action of gas flow field. The geometry of three-nozzle has a significant influence on the characteristics of the interference flow field. The influence of different distance (L) and axis angle (theta) between two adjacent paint holes on the interference gas flow field and coating thickness distribution are analyzed by changing the structure of three-nozzle. Numerical simulation results show that small L and theta result in strong interference effect, while the paint is mainly concentrated in the central region of the target, which is easy to cause overspray. With the gradual increase of L and theta, the strength of interference gradually decreases and the paint gradually spreads to both sides. However, the strength of interference would become very small when L and theta get too large, which is easy to cause an uneven coating film. According to the numerical simulation results, the best spraying effect can be obtained when L = 40 mm and theta = 30 degrees. Compared with single-nozzle and double-nozzle, the effective coating film width of three-nozzle has increased by 414.3% and 176.9%, respectively, which improves the spraying efficiency.