Research On Fluid-elastic Instability In Tube Bundles Subjected To Two-phase Cross Flow

The shell-and-tube heat exchangers are widely used in process industries,such as chemical,petrochemical,food,metallurgy and pharmaceutical.The vibration damage of tube bundles has become one of the main reasons for the failure of shell-and-tube heat exchangers,and among the mechanisms of flow-induced vibration,the fluid-elastic instability is the most common and destructive.Although a lot of experimental researches on fluid-elastic instability of tube bundles in two-phase flow had been carried out,due to the complexity,up to now,no widely applicable design guidelines on fluid-elastic instability in tube bundles subjected to two-phase cross flow had been obtained.In this paper,the fluid-elastic instability of the tube bundles in two-phase cross flow was studied by the combination of experiment and numerical simulation.In experimental study,the effects of flow conditions of the two-phase flow and geometric characteristics of the tube bundle on the damping and fluid-elastic instability were studied respectively.Then,a method for correcting the pitch velocity based on CDM(Conductivity Difference Measurement)model was proposed,from the perspective of the configuration of tube bundles,the recommended values of the instability constants were obtained when the void fraction was lower than 50%,expecting to has certain reference significance for theoretical research and engineering design of the vibration of heat exchanger tube bundles.In aspect of numerical simulations studies,a bi-directional fluid-structure interaction model of flow-induced vibration of tube bundles was established.According to the characteristics of the fluid flow between the tube bundles,the influence of pitch-to-diameter ratio and configuration on fluid-elastic instability was interpreted.The experimental study found that,in the four configurations,the parallel triangular tube bundles have the largest damping ratio,but it is the most prone to fluid-elastic instability.The stability of the four configurations from high to low is:normal triangular,square,rotated square,parallel triangular.For the square and normal triangular,the recommended instability constant is 4.0,for the rotated square and parallel triangular,when the mass damping parameter is less than or equal to 0.45,the recommended instability constant is 0.68,conversely,the recommended instability constant is 1.5.