Study On Vibration Characteristics Of Heat Exchanger Tube Bundles Under Pulsating Flow Condition

Heat exchanger is process equipment which is widely used in petroleum, chemical,electric power, food and other industries. Safe operation of the equipment has a greatinfluence on industrial production. With the gradual expansion of production scale, shelland tube heat exchanger used in industrial production is a growing tendency in the largescale. Then, the span of non-supported tube bundle increases, and the rigidity of heatexchanger decreases. In order to improve heat transfer efficiency, fluid velocity is gettingfast. As a result, the destruction phenomenon of heat exchanger is increasing due to theflow-induced vibration. Pulsating flow technology improves heat transfer efficiency of heatexchanger, but additional fluid vibration effects are brought at the same time. The study onvibration characteristics of heat exchanger under pulsating flow condition is of greatsignificance for making equipment work properly.The experimental heat exchanger is firstly studied in this paper. Vibrationcharacteristics of the heat exchanger are analyzed by fluid-structure coupling method undernon-pulsating flow and pulsating flow conditions. On the one hand, the modalcharacteristics of the heat exchanger are researched under the two conditions. On the otherhand, according to the different roles of fluid in the heat exchanger, the heat exchange tubeis carried on harmonic response analysis under non-pulsating flow condition, and transientAnalysis under pulsating flow enhanced conditions. The results show that the modal shapeof the heat exchange tube is similar and the natural frequency of that is also very close inboth conditions, which explains the changes of the external flow field have little or noeffect on natural vibration characteristics of the heat exchange tube in fluid environment.Moreover, reducing the sine function coefficient and the constant term in pulsating flowload will be helpful for avoiding vibration failure of the heat exchange tube.Based on the vibration analysis of the experimental heat exchanger, a shell and tubeheat exchanger designed in a company is analyzed as the research object. The vibration effect that pulsating flow technology takes in the heat exchanger is researched, and then thevibration characteristics of the heat exchanger under non-pulsating flow and pulsating flowconditions are compared and analyzed. Porous media model is applied to simulate the shellflow field. Through simplifying calculation model, the natural frequency of heat exchangetube is calculated by GB151-1999and the finite element analysis software ANSYS. Thefinite element model of the heat exchange tube is determined by comparing these methods.The factors affecting the natural frequency of single tube and tube bundle were researchedas well as the vibration law of heat exchange tube. The modal analysis of the heatexchanger is further conducted by fluid-structure coupling method. Then shell velocityobtained under non-pulsating flow conditions is converted into the load that acts on thecorresponding heat exchange tube surface to do harmonic response analysis. Meanwhile,the heat exchange tube is carried on transient Analysis under pulsating flow enhancedconditions in order to obtain the stress distribution state of the tube and predict thevibration failure location of the tube. It is shown that the natural frequency of heatexchange tube will vary with the change of the diameter, wall thickness, the baffle platespacing and the pitch diameter ratio of the tube. According to the different constraints, theheat exchange tube is divided into A, B and C tube. The end of A tube is the easiest toproduce strength failure, and the intermediate position of C tube is easier to producecollide due to larger amplitude under non-pulsating flow conditions. However, thevibration amplitude of A tube near the shell entrance is larger than B tube and C tube,where is the easiest to produce vibration damage under pulsating flow conditions. What’smore, reducing loading coefficient of pulsating flow function is effective to avoid thevibration failure of the heat exchange tube.