| Flow-induced vibration achieves the purpose of passive vibration heat transfer enhancement using the tube vibration when the fluid flows across the elastic tube bundle.However,the fatigue damage of elastic tube bundle occurs due to the vibration generally.Therefore,it is significant to take into account the flow-induced vibration in heat transfer enhancement and fatigue strength.The research work in this paper focus on the flow-induced tube vibration in the shell-side of planar elastic tube bundle heat exchanger.The flow-induced vibration in heat transfer enhancement and fatigue strength of tube bundle was thoroughly studied using field synergy principle and multi-axial fatigue analysis.The prediction correlation of heat transfer enhancement by flow-induced elastic tube bundle vibration was established and the diagram for determining the tube fatigue was introduced.The vibration response of elastic tube bundle in distributed pulsating flow field,coupled flow field and steady flow field was studied using experimental method.The vibration heat transfer enhancement of elastic tube bundle in these three flow fields was investigated using numerical method.The research work in this paper is of great significance to the design and application of elastic tube bundle heat exchanger.The research work in this paper is summarized as follows,(1)It does not take into account the flexibility and vibration of tube bundle.The convective heat transfer in shell-side of single and multiple rows rigid tube bundle was numerically simulated when Reynolds number was in the range of 200-1000.Then,the effect of Reynolds number and geometry parameters on the heat transfer in shell-side of single and multiple rows rigid tube bundle was studied when the tube spacing was in the range of 20-30mm and the tube row spacing was in the range of 50-70mm.At last,the heat transfer prediction correlation of multiple rows rigid tube bundles was developed using the multiple regression analysis of MATLAB software.Results show that the efficiency of energy consumption should be taken into account when increasing the Reynolds number in shell-side to enhance heat transfer because the effect of Reynolds number on pressure drop is greater than that on heat transfer coefficient.Within the range of research parameters in this paper,the effect of tube row spacing on convective heat transfer in shell-side of multiple rows rigid tube bundles can be ignored because the tube row spacing is greater than the threshold of tube row spacing(3.25D-4D).The tube spacing mainly affects the change of pressure drop in shell-side of multiple rows rigid tube bundles and the heat transfer performance shows that the tube spacing 20mm is the optimal tube bundle configuration in this paper.At last,based on the effect of geometry parameters and Reynolds number on the convective heat transfer in shell-side of multiple rows rigid tube bundles,a new heat transfer prediction correlation of multiple rows rigid tube bundles is developed,Nu=0.036Re0.72Prf0.36(Prf/Prw)0.25?(2)The heat transfer enhancement by shell-side flow-induced vibration was calculated using the sequential solution method of bi-directional fluid structure coupling.Then,the heat transfer enhancement by shell-side flow-induced vibration and the heat transfer performance in different inlet velocity and geometry parameters were studied using field synergy principle.At last,a prediction correlation of heat transfer enhancement by flow-induced vibration was derived using dimensionless analysis including Reynolds number and vibration Reynolds number.Results show that the oscillating relative velocity and the improvement of field synergy level are the crucial factors for heat transfer enhancement by flow-induced vibration.Among which,the improvement of field synergy plays a dominated role on the heat transfer enhancement.The augmentation 6.5%in Nusselt number of elastic tube bundle occurs owing to the improvement 6.01%in field synergy level.The value of heat transfer enhancement by flow-induced vibration decreases with the increase in fluid flow.In the range of 0.2-0.5m/s,the Nusselt number of elastic tube bundle is enhanced by 8.26%,6.07%,5.67%and 3.91%,respectively.Meanwhile,the maximum and minimum PEC is 1.08 and 1.03,which means that the heat transfer coefficient is augmented sometimes by increasing the fluid flow.The middle two elastic tube bundles perform better capability to enhance heat transfer.When the inlet velocity is 0.2m/s and 0.5m/s,the average Nusselt number of middle two tubes is augmented 12.97%and 4.58%,respectively.The average Nusselt number of innermost and outermost tubes is augmented 5.37%and 2.4%,respectively.The heat transfer enhancement by flow-induced vibration increases with the decrease in the tube wall thickness and the increase in tube spacing.This is similar to the change of vibration Reynolds number.Therefore,the maximum augmentation 14.3%and 28.8%occur in the Nusselt number of elastic tube bundle when tube wall thickness is 0.75mm and tube row spacing 30mm,respectively.The maximum threshold of tube row spacing is enlarged from 4D to 6D due to the effect of flow-induced vibration.Based on the results of heat transfer enhancement in different fluid flow and geometry parameters,the prediction correlation of heat transfer enhancement by flow-induced elastic tube bundle vibration including Reynolds number and vibration Reynolds number is developed,(Nuv/Nu)-1=0.036(Rev/Re)1 584((?/D)0.14?(3)The stress distribution of elastic tube bundle subjected to flow-induced vibration was calculated.The multi-axial fatigue analysis of elastic tube bundle was conducted based on the characteristics of dangerous part in elastic tube bundle.The safety factor of elastic tube bundle was calculated according to the Von Mises stress criterion.Then,the diagram for determining the tube fatigue was introduced.The change of fatigue strength in the tube wall thickness 0.75-1.5mm and tube spacing 20-30mm and the heat transfer enhancement by flow-induced vibration in high inlet velocity 1-3m/s were all studied.The range of vibration parameter in elastic tube bundle was obtained for satisfying the fatigue strength and achieving the heat transfer enhancement.Results show that the dangerous part of elastic tube bundle usually locates at the bend of the innermost tube,which is subjected to the multiple-cyclic loads of moment and torque.The vibration amplitude plays a greater effect on fatigue strength of tube bundle by flow-induced vibration.The safety factor decreases with the increase in vibration Reynolds number.Therefore,the minimum safety factor is 14.3 and 6.7 when tube wall thickness is 0.75mm and tube spacing is 30mm,respectively.The elastic tube bundle will not be damaged by fatigue because the stress response locates at the safe region of the diagram for determining the tube fatigue.Within the range of research parameters in this paper,elastic tube bundle can satisfy the fatigue strength and achieve the heat transfer enhancement in the range of vibration Reynolds number 147-780 when Reynolds number is in the range of 100-900.(4)The vibration response of elastic tube bundle in distributed pulsating flow field,coupled flow field,shell-side steady flow field was studied experimentally.Meanwhile,the fatigue strength,the vibration heat transfer enhancement and the comprehensive heat transfer performance of elastic tube bundle were investigated numerically.The advantage of coupled flow field in heat transfer enhancement by flow-induced vibration was compared.Finally,the CAE-aided design of distributed pulsating flow heat exchangers was introduced.Results show that the maximum vibration amplitude of elastic tube bundle occurs in the pulsating flow field.The vibration amplitudes of the big and small connectors are reduced by 18.5%and 51.7%in the coupled flow field and 62.2%and 59%in the shell-side steady flow field.In the coupled flow field,along the counterclockwise direction of middle tube bundle,the acceleration vibration amplitude of 25Hz decreases first and then increases.The acceleration vibration amplitude of 43Hz increases first and then decreases.In the outermost tube bundle,the acceleration vibration amplitude of 24Hz performs the increasing tendency.The acceleration vibration amplitude of 43Hz increases first and then decreases.Meanwhile,the vibration response component of the middle tube bundle is more complicated containing the components of high-frequency vibration.As a result,the vibration Reynolds number decreases first and then increases in middle tube bundle,and gradually increases in the outermost tube bundle.The elastic tube bundle fatigue strength is satisfied and the vibration heat transfer enhancement is obtained in distributed pulsating flow.The greatest safety factor and higher heat transfer coefficient in elastic tube bundle occur in the coupled flow field.Meanwhile,the heat transfer coefficient difference in each row elastic tube bundle is reduced from 55.3%to 2.2%and the transfer coefficient per unit flow rate is enhanced 3.5 times. |
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