Since 1933, the vortex tube (VT) has been used as a device for cooling, heating, and creating separation process (particles, hydrocarbons, energy, etc.). The VT efficiency is very relevant to the characteristics of the inside fluid flow patterns. The most important part in the VT that directs the fluid flow is the “navigator,” which has an angle and a rounded edge. In this study, the effects of change in the radius of the rounded edge (R* = 0, 0.5, 1, 1.5, 2, and 2.5 mm) on flow patterns and thermal performance of the VT are studied experimentally. The results show that with a rounded radius variation from 0 to 2 mm, the VT cooling efficiency increases sharply (34.84%) and with a further increase, there will be a decreasing trend for the cooling efficiency (10.48%). Also, this radius affects the location of the effective cold mass fraction (CMFs related to the highest thermal performance). In addition, variations in the gas velocity (axial/swirl at two positions Z/L = 0.3, 0.7) were studied with complete details and compared with other researchers' valid reports. As the results, the maximum axial velocity near the chamber and the maximum swirl velocity drop along the tube are effective on better cooling/heating performance.