Research On Fluid-elastic Instability Of Rotated Triangular Tube Bundles Subjected To Two-phase Cross Flow

The shell-and-tube heat exchangers are widely used in chemical,power,pharmaceutical and other industries.Fluid induced vibration is the most important reason of failure.Among the four mechanisms of fluid induced vibration,the fluidelastic instability is the most destructive.For the tube bundle vibration induced by the two-phase cross flow,many researchers have conducted related research,but have not reached a completely consistent conclusion.Moreover,most of the existing researches is about square and triangle arrangement,but there are few studies on rotated triangle arrangement which is the most prone to fluid-elastic instability.Therefore,it is of great significance to study the vibration characteristics of rotated triangle tube bundles.This paper conducted fluid-elastic instability of rotated triangular tube bundles subjected to two-phase cross flow from experimental research and numerical simulation.Firstly,a single flexible tube surrounded by rigid tube bundles was studied,and the difference in vibration characteristics between the lift and drag direction was analyzed.Then,rotated triangular tube bundles with a pitch-to-diameter ratio of 1.25 to 1.6 were studied.The difference of vibration characteristics between lift and drag directions and the vibration characteristics of different positions in the tube bundle were analyzed.The results show that for the tube bundle with a pitch-to-diameter ratio less than 1.5,the critical flow velocity in the lift direction is smaller than the drag direction,the tube at the inlet of the flow field is more likely to occur fluid-elastic instability.For the tube bundle with a pitch-to-diameter ratio greater than 1.5,the critical flow velocity in the lift direction is greater than the drag direction,and the tubes at different positions occur fluid elastic instability at the same time.Secondly,a two-way fluid-structure coupling model of rotated triangular tube bundles was established.The influence of solid deformation on the flow field was considered in the numerical simulation,so that the mathematical model was closer to the actual process.Fluid induced vibration was simulated by the model,and the velocity distribution and pressure distribution of the flow field were obtained.The rms amplitude of numerical simulation and experiment was compared.At the same time,the peak frequency of the spectral curve of the numerical simulation and experiment was compared.The results show that the date of numerical simulation is in good agreement with the experimental data.Through the analysis of the velocity streamline diagram,the flow characteristics of the flow field and the vibration characteristics of rotated triangular tube bundles are explained.Finally,the fluid elastic instability of rotated triangular tube bundles under twophase flow was studied.The damping ratio of fully flexible tube bundles and a single flexible tube surrounded by rigid tube bundles was compared.The effects of vibration direction,gap flow velocity and void fraction on the damping ratio were analyzed.The effect of the pitch-to-diameter ratio,void fraction and arrangement on the critical flow velocity was studied.The smaller the pitch-to-diameter ratio,the more easily the fluidelastic instability occurs;at the same pitch-to-diameter ratio,the rotated triangular and the rotated square are most prone to fluid-elastic instability,followed by square,and the triangular is the most stable.The design guidelines for rotated triangular tube bundles under two-phase flow were proposed.For rotated triangular tube bundles,when the mass damping parameter is less than 1,the recommended instability constant is 2.48.When the mass damping parameter is greater than 1,the recommended instability constant is 3.