Heat transfer performance of internal flow by inserting punched and non-punched vortex generators

This article proposed a new arrangement of planar vortex generators (VGs) and punched VGs within a heated tube. The airflow and heat removal performance of the VGs with new configurations were studied by numerical simulation and experimental methods in turbulent flow (6060 similar to 21, 210), and compared with two commonly used arrangements of VGs in tubes (tube fitted with all planar VGs and all punched VGs). The punched VGs used were with three perforation indexes of PI = 7.8%, 15.2%, 46.6%, and three-pitch ratios of PR = 1.63, 3.27, 4.89. An interesting discovery in the case of tubes fitted with VGs in the new configuration was that the strength of main longitudinal vortices displayed a periodic change from weak to strong along the mainstream direction, which presented relative low-pressure loss and poor thermal performance as well. The results indicated that when VGs had the same area holes, there was little difference between the heat enhancement factor (TEF) value of tubes fitted with three arrangements VGs when Re > 10, 000. Moreover, the increased area of punched hole resulted in poor heat removal rate and lower pressure loss and the smaller the PI was, the larger the TEF. Additionally, the TEF value increased with the decrement of PR. In most Re number ranges, the TEF values were lower than 1.0. The highest TEF of 1.44 was reached by utilizing the punched VGs with PI = 7.8%, PR = 3.27 at Re = 6060.