Recently, plasma arc welding (PAW) was widely applied in the industry. The main reason is that it can produce high energy density are which reduces the rate of porosity and residual stresses. Also, it is cheaper than electron beam and laser beam welding machines. Therefore, PAW processes are utilized in fabricating the aerospace and the nuclear equipment. According to the literature; the central temperature of a plasma arc can be as high as 16650℃～27770℃. The excessively high temperature may cause damage to the torch. It is difficult to directly measure the temperature distribution in the torch by experiments. Therefore a computational fluid dynamics (CFD) package is used as the tool in this study. The flow and temperature fields of a commercially available Nippon Steel PAW torch are analyzed first. From its drawbacks, new cooling design concepts are then proposed which utilize annular swirling flow and a U-shaped duct in the coolant channel. Finally, computational analysis on the improved cooling design is conducted, and the results are compared with those of the Nippon Steel PAW torch. Results show that due to non-axisymmetric inlet and outlet arrangement of the cooling water channel in the Nippon Steel PAW torch, a hot spot on the nozzle surface can occur. In the improved cooling design, an appropriate U-shaped curved channel can cause flow redistribution so that the fluid velocity near the channel outer wall is increased. Flow swirling also has the effect of increasing heat transfer rate. These factors cause the averaged torch surface temperatures in the improved design to be lower than those of the Nippon steel PAW torch, indicating the new design may give longer lifetime for the torch.
Plasma arc welding Swirling flow Curved channel CFD