Abstract: Heat transfer enhancement is achieved by flow-induced vibration in elastic tube bundles heat exchangers. To recognize the vibration characteristics of heat transfer element under the action of fluid-solid coupling has important significance to the study of heat transfer enhancement mechanism and to the optimization of tube bundle structure. The finite element method is used to study the vibration characteristics of planar elastic tube bundle under the action of fluid flow in the tube. The rigid connectors are simplified by multi-points constraint equation. The element matrix and tube bundle vibration equation are achieved via the coordinate transformation of the four pipes. The frequency variation and vibration mode characteristic of planar elastic tube bundle is analyzed at different rates of fluid flow in the tube, and the critical flow rate of vibration buckling is achieved. The results show that the fundamental frequency of tube bundle decreases obviously with the increase of flow rate, and the critical flow rate of vibration buckling is 3.356 5～3.356 9 m/s. There are two vibration modes of planar elastic tube bundles：In-plane and out-plane vibrations.

Key words: Finite element method, Fluid-solid coupling, Planar elastic tube bundle, Vibration characteristics