Flow Visualization and Dynamics of Heat Exchanger Tube Arrays in Water Cross-Flow

Abstract

<p>A flow visualization technique has been developed to investigate the flow developments in tube arrays over a wide range of Reynolds numbers. The techniques is non-obtrusive and permits observations deep inside a tube bundle where the flow is unaffected by free surface or boundary effects. The technique has been used to examine flow behaviour in a rigidly and flexibly mounted square in-line and rotated square arrays in a water cross-flow. The important case of a single flexible tube in an otherwise rigid bundle, which received considerable attention in the literature, has also been examined. Results pertinent to vortex shedding, turbulence and fluidelastic instability are given which include response curves and frequency spectra together with flow visualization films and photographs.</p> <p>The results indicate that discrete alternate and symmetric vortex shedding can occur within the confinement of a tube bundle. Increased turbulence, as more rows are traversed by the flow, has a detrimental effect on the discrete vortex structures. Vorticity shedding and turbulence coexist as separate phenomena however, vorticity shedding is identified as the mechanism responsible for the observed resonance peaks in the response curves. Vortex shedding and the associated flow induced response in the square array is different from that in the staggered rotated square array. Fluidelastic instability is associated with marked increase in the transverse response amplitude and significant flow redistribution although it appears random in a full flexible bundle. Finally, a single flexible tube in an otherwise rigid bundle will become unstable at essentially the same flow velocity as that when the surrounding tubes are free to move. The response is predominantly in a transverse direction with significant flow redistribution. The motion of the redistributed flow lags behind the tube motion.</p>