Abstract: Heat transfer enhancement is achieved by fluid-ind- uced vibration in elastic tube bundles heat exchangers. To understand the vibration mechanism and improve further the performance of elastic tube bundles, it is important to identify its modal property. Equations of motion of each component are derived firstly, and then the components of the system are assembled together according to the compatibility condition of displacements. Thus, the differential equation of free vibration in terms of principal modal coordinates for elastic tube bundles is obtained. The natural frequencies and mode shapes are got by solving the equation of motion with numerical methods. The characteristics of mode shapes are analyzed. The results show that the in-plane vibration co-exists with the out-plane one. The vibration of elastic tube bundles is the combination of vibrations in different directions as a result of complex excita- tion in actual internal and external fluid field. The mechanism of heat transfer enhancement for elastic tube bundles is investigated elementarily.

Key words: Component mode synthesis method, Dynamic characteristics, Elastic tube bundles