Manufacturing of three-dimensional inner finned tube using three-skewed rolling and wedging/extruding forming

Finned tubes are widely used to enhance the heat transfer performance of shell-and-tube heat exchangers. Three-dimensional inner finned tubes (3D-IFTs) significantly improve convection heat transfer inside the tube. However, the manufacturing of 3D-IFT has been challenging. A combined forming method – three-skewed rolling and wedging/extruding method is proposed for their manufacture. In this method, spiral inner fins were initially fabricated under rolling jointly exerted by the three-skewed roller uniformly distributed around the base tube and a mandrel with helical teeth inside the base tube. Then, the spiral inner fins were wedged and extruded into 3D inner fins by a specially designed tool. During this process, the base tube was driven to rotate and move axially forward by the three-skewed roller. The kinematics of the three-skewed rolling and wedging/extruding were also analyzed. The results showed that the wedging/extruding depth did not exceed a critical wedging/extruding depth, and the relative depression of the roller blade remained within the allowable limits. Finally, the processing experiments were conducted. The study reveals that a greater feed rate and wedging/extruding depth should be selected to achieve taller fin and a larger pitch.