The Crossing Frequency As a Measure of Heat Exchanger Support-Plate Effectiveness

Author: Au-Yang M.K.  

Publisher: Academic Press

ISSN: 0889-9746

Source: Journal of Fluids and Structures, Vol.16, Iss.1, 2002-01, pp. : 83-92

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Abstract

The crossing frequency is the number of times per second the vibration amplitude crosses the zero displacement line from negative displacement to positive displacement. In flow-induced vibration in which the motions are often random and/or a number of modes contribute to the vibration amplitudes, the crossing frequencies are modal-weighted average frequencies of the vibration. It is postulated in this paper that the crossing frequency can be used as a measure of heat exchanger support-plate effectiveness. Using a time-domain, nonlinear analysis technique, the crossing frequencies of a tube vibrating in support plates with oversized holes can be computed as a function of time and the tube-to-support-plate clearances. It was found that the fluid–elastic stability margin of a tube bundle, in the context of the original Connors' equation for tube bundle fluid–elastic instability, should be independent of the tube-to-support-plate clearances. A simple method of estimating the critical velocity based on the time-domain equation of fluid–elastic stability is suggested.