NUMERICAL SIMULATION OF HEAT TRANSFER AND PRESSURE DROP CHARACTERISTICS IN TWISTED OVAL TUBES

The numerical research aims to investigate the heat transfer performance difference between the twisted tube and the smooth tube at the same hydraulic diameter. The effect of the major/minor axis ratios on the fluid-flow inside the twisted oval tube is studied in the Reynolds number range of 3000-11000, and the integral thermal-hydraulic effectiveness of twisted oval tubes is evaluated. The results show that the twisted wall induces secondary flow perpendicular to the mainstream direction. The vortices are rapidly generated in the pipe-line when the fluid enters the twisted tube section from the upstream section. As the fluid develops further, the vortices converge to form a spiral flow. Numerical simulations indicate that the average Nusselt number of twisted oval tube with a major/minor axes ratio of 1.70 increases by 18.7-35.5%, while the pressure drop increases by 59.9-61.3% compared to smooth oval tube. Furthermore, as the major/minor axes ratio increases from 1.18-2.48, the average Nusselt number experiences an increase of 26.7-38.2%. The twisted tubes within the major/minor axes ratio range of 1.40-1.96 demonstrate superior integral thermal-hydraulic performance compared to other pipes.