The Study On The Stochastic Characteristics Of Fluid Elastic Instability Of Heat Exchanger Tube Bundles

In all classes of shell-tube heat exchangers, the tube bundles are the most flexible elements. The flow inside or outside the tubes always induce tube bundles to vibrate. Fluid elastic instability among the several flow-induced theories is the main cause of the tube bundles vibration at a medium high velocity of the cross flow. As the working state of heat exchanger is so complicated that the random contact condition between tube bundles and support plates is hard to predict. That will seriously affect the natural frequencies and vibration modes of tube bundles. Therefore, the study on the fluid elastic instability of tube bundles with invalid supports has been an important topic to improve the reliability of shell-tube heat exchangers.In this paper, following main work has been done. Firstly, the fluid elastic instability mechanism models of tube rows and tube arrays have been made. The critical cross flow velocity coefficients of tube rows and tube arrays were deducted, respectively. Then the coefficients were used to calculate the critical velocities of tube rows, in-line tube arrays and staggered tube arrays of different pitch-to-diameter ratio comparing with the GB151 calculating results to test this method.Secondly, it is considered that each mode of one tube is fluid dynamically coupled to all the N modes of adjacent tubes to explain experimental phenomena that the fluid elastic instable vibration appears not in the lowest mode but in high-order modes. And the conservative working cross flow velocities are given.Next, mechanism modeling of single tube has been accomplished. The vibration characteristics of all-support-valid state are figured out in analytic method. Those of other states are calculated in Matlab program in the assumed mode method. The results can be substituted into the critical velocity computational formula directly. And the stochastic characteristics can be calculated using the manufacturing errors and theoretical gap between tube and support plate.At last, all the analyses above are united to calculate the probabilities of fluid elastic instability happening to single tube of every possible supporting states so that the holistic instability can be evaluated. Then comes the preventive measures.