| The elastic tube bundle heat exchanger utilizes the fluid to induce the vibration of elastic tube bundle to realize heat transfer enhancement.Compared with planar elastic tube bundle,conical spiral elastic tube bundle is easy to realize flow-induced vibration due to its low natural frequency.The stress distribution is uniform when tube bundle is vibrating,the amplitude of alternating stress is small and it is less prone to fatigue damage.The helical structure of the tube bundle causes the tube-side fluid to be affected by the centrifugal force during the spiral flow,forming a secondary flow vortex and it is conducive to convective heat transfer enhancement.In this paper,the vibration responses and heat transfer enhancement of conical spiral elastic tube bundle were numerically studied,the experimental device was constructed and the vibration responses were tested by tube-side flow-induced vibration.The research work is of great significance to realize the control of vibration induced by tube-side flow and the design improvement of elastic tube bundle heat exchanger.The main work of this paper is as follows:(1)The two-dimensional simulation models of flow around cylindrical,triangular column and cylindrical splitter were established,and the change of the resistance coefficient and the frequency of the pulsating flow and the intensity of the pulsating flow were studied.The influences of splitter length on variation of the frequency and intensity of the pulsating flow were analyzed.The results show that the integrated flow characteristics of the fluid around the triangular column are better than those of the cylinder,and flow around equilateral triangle column is better than right triangle column and obtuse triangle column.Changing the length of the triangular column or the length of the cylindrical splitter can adjust the frequency of the pulsating flow.(2)The geometrical model of conical spiral tube bundle and tube side and shell side fluid domain were established.The natural mode of tube bundle and the tube bundle’s vibration responses of flow induced vibration were analyzed.The results show that elastic tube bundle’s mode of vibration is divided into transverse vibration and longitudinal vibration,mainly in the longitudinal vibration.When the tube side velocity is in the range of 0.1m/s-0.6m/s,with the increase of flow rate,the frequency of vibration induced by the fluid is almost constant and the amplitude of the vibration displacement increases gradually.When pulsating element is fixed on tube side,the amplitude of conical spiral tube bundle increase by 6.8%at low velocity rate.(3)The experiment table was constructed for the purpose of studying the tube-side vibration responses in conical spiral elastic tube bundle,and the vibration responses and vibration trajectory of the monitoring point were tested,the correctness of numerical simulation method was verified.The results show that the tube bundle’s main frequency of vibration at the monitoring point of the fluid-induced vibration is 6Hz in the range of 0.1m/s-1.2m/s,and the first-order natural frequency is 5.97Hz,near the elastic tube bundle’s natural mode.The movement of the tube bundle’s joints create a complex space.The maximum amplitude relative error between experimental value and the simulation method result is about 10%.(4)The heat transfer model of conical spiral tube bundle was established,the influence of tube bundle structure on heat transfer was analyzed,the flow field distribution characteristics of the tube bundle were studied,and the heat transfer characteristics of the elastic tube bundle under the tube side fluid were analyzed.The results show that the diameter of the elastic tube bundle increases,the heat transfer coefficient decreases.The higher conical degree is,the higher the heat transfer coefficient is.When pulsating element is fixed on tube side,the PEC of conical spiral elastic tube bundle is 1.1 times than no pulsating element at low flow rate. |
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