Fluidelastic Instability in Shell and Tube Heat Exchangers: A Framework for a Prediction Method

摘要

A framework for a method to predict fluidelastic instability in heat exchanger tube bundles is presented. The method relies on a three-dimensional, cylindrical coordinate, thermal-hydraulic analysis code to obtain a representation of the three-dimensional flow distribution within the heat exchanger. With this information, local crossflow velocities corresponding to each tube in the exchanger are obtained by interpolation and resultant crossflow velocity distributions are computed. With a knowledge of the vibration mode shapes and frequencies, reduced effective crossflow velocities are then computed for each tube. A comparison with experimental results shows excellent agreement: the tubes with high values of predicted reduced effective crossflow velocity are the same tubes that first experience fluidelastic instability in the flow tests and vibrate most violently; also, the simulation correctly predicts that the tubes directly exposed to the flow from the inlet nozzle have a low potential for fluidelastic instability. Very good agreement is also shown in the comparison of the predicted reduced effective crossflow velocities with the critical value obtained from a design guide. In summary, the feasibility of developing a heat exchanger tube vibration prediction method, based on a computer simulation of flow distribution, is demonstrated. Such a method would have immediate application in design optimization. However, further development and evaluation are required. (ERA citation 08:020961)