Elastoplastic analysis of hydraulic fin-tube expansion via a bilinear simplified material model

Fin-tube heat exchangers are one of the most common types of industrial heat exchangers. Tube expansion, a crucial manufacturing step in the production of these exchangers, plays a significant role in determining their performance. In this paper, a mathematical model is developed based on elastoplastic theory to describe the deformation and pressure at different stages of the tube expansion process in fin-tube heat exchangers. The model simplifies the fin and heat exchange tube into a double-cylinder structure and uses a bilinear hardening model. This study focuses on the tube expansion process of S304 heat exchange tubes and Al8011 fins, investigating the deformation and pressure during expansion through both experimental and numerical methods. The theoretical calculations show that the radial deformation of the heat exchange tube and fin is approximately 0.60 mm and 0.36 mm, respectively, while the residual contact pressure after expansion is around 4.0 MPa. A comparative analysis of the experimental and simulation results reveals that the errors between the mathematical model's calculations and the measured/simulated values are within 11.21% and 7.99%, respectively. This demonstrates the accuracy and reliability of the mathematical model, offering valuable insights for research on the tube expansion process.