A STUDY ON FLUIDELASTIC VIBRATIONS OF TUBE ARRAYS SUBJECTED TO CROSSFROW IN HEAT EXCHANGERS

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A vast number of papers have been published on the fluid-elastic vibrations of heat exchanger tube arrys subjected to crossflow, in almost all of which the hydrodymanic coefficients necessary to evaluate critical flow velocities are obtained experimentally. In this study it is aimed at obtaining the hydro-dynamic coefficients analytically by using the leakage-flow theory developed by the author. The results obtained are as follows.1.The measurements of pressure distribution in the streamwise direction in the three-row tube array show that the total pressure drop occurs at the first row. This fact means that the firsst row acts like a row of nozzles in impulse turbines. The minimum pressure occurs at the minimum gap and then the flow separates from the tube walls at about 5-10 degree after the minimum gap. The second row receives velocity energy and the pressure rises just before the minimum gap and then drops again after the minimum gap.2.Fluid forces acting on a tube in one-row tubes when it vibrates in the row direction are calculated by using the leakage-flow theory and compared with the experimental results obtained by Tanaka. Fairly well agreement is obtained, which confirms the validity of applying the leakage-flow theory for gap flow between tubes.3.Stability analysis shows that at gap velocity instability is caused by fluid negative damping, and that at high gap velocity whirling mode instability occurs. The latter is caused by velocity-squared fluid-stiffness, where the critical velocities are proportional to the root of mass damping parameters.4.Resonant pressure pulsations in the stremwise direction occur with high sound level in the duct containing tube array in a certain range of flow rate.