Study On The Influence Of Heat Exchanger Tube Stiffness On Fluid-elastic Instability

Tubular heat exchangers are widely used in chemical production because of their many advantages. However, problems of flow induced vibration become more serious as heat exchangers become larger and attract extensive attention of researchers at home and abroad. Fluid-elastic instability is the most important and destructive mechanism for flow induced vibration. So conducting experiments on fluid-elastic instability of heat exchanger tubes has important theoretical significance and engineering value for application.First, vibration responses of a single flexible tube in rigid arrays and fully flexible arrays with a pitch to diameter ratio of 1.28 were tested in water tunnel. The test arrays consist of four patterns: normal triangular, rotated square, rotated triangular and normal square. Vibration responses of a single flexible tube at different locations in a rigid array were compared with those of tubes at the same location in a fully flexible array to verify the applicability of the simplified method of a single flexible tube in a rigid array for the tube array with a pitch to diameter ratio of 1.28 in water. The results show that the locations of unstable tubes are different between the rigid array and the fully flexible array which have the same pattern. And the spectral response, orbits and main vibration direction of the tube at the same loaction in the rigid array are different from those in the fully flexible array, too. So it can be concluded that for the array with a pitch to diameter ratio of 1.28 in water, the simplified method of a flexible tube located in a rigid array cannot be used to study the fluid-elastic instability of the tubes in a fully flexible array.Then, the influence of the location, number and stiffness of the variable-stiffness-tubes on the fluid-elastic instability were also studied here to provide references for engineering practice applications. Experiments were conducted on a fully flexible normal square tube array with a pitch to diameter ratio of 1.28.The vibration characteristics after changing the stiffness of some tubes were compared with those before changing. The results show that, compared with the previous case, when the upstream tube stiffness is changed, the amplitude of the measuring tube is weakened to some extent in the transverse direction and the weakening effect of changing the downstream tube is not significant as that of changing the upstream tube. With increasing the number of upstream variable-stiffness-tube, the weakening effect increases, too. The weakening effect of decreasing the upstream tube stiffness is more obvious than that of increasing the upstream tube stiffness. There is no obvious regulation between the critical velocity of the mearsuring tube and the location, number or stiffness of the variable-stiffness-tubes.