A SIMULATION OF THE TURBULENCE RESPONSE OF HEAT EXCHANGER TUBES IN LATTICE-BAR SUPPORTS

Tube failures due to excessive flow-induced vibrations are a major concern with regards to the operation of heat exchangers in nuclear power and chemical process plants. Among the possible excitation mechanisms, turbulence-induced forces have a persistent effect and thus are an important factor in determining the long-term reliability of heat exchangers. Impact forces which occur when tube/support collisions take place play a vital role in determining tube wear. To address this issue, a tube/support interaction model was implemented in an in-house finite element program and validated against three published examples. Pseudo-forces in conjunction with modal superposition were utilized in solving the nonlinear equations of motion of loose tubes in lattice-bar supports. Time-domain simulations of the nonlinear response of the tube are presented to determine the effect of various tube and support parameters on the vibratory characteristics of the systems. Special attention was paid to the effect of increased clearance on the response of tubes in lattice-bar supports. The tube response, impact force and contact ratio were analysed and represented in dimensionless form. The dimensionless parameters developed proved effective in collapsing the data pertaining to different flow velocities over single curves. These are useful in identifying the roles of several key variables in altering tube dynamics. Moreover, these parameters may also be used to scale the results to account for differences in geometrical and material properties.