Experimental Research on Fluid-Elastic Instability in Tube Bundles Subjected to Air-Water Cross Flow

Abstract

Fluid-elastic instability is the major factor in causing the vibration of tube bundles. Design guidelines on fluid-elastic instability in tube bundles is necessary to avoid damage due to excessive tube vibration. However, the design guidelines on fluid-elastic instability in tube bundles subjected to two-phase cross flow have no consistent conclusions. Accordingly, this technical note researches the vibration characteristics of three tube bundle distributions, namely, normal square tube bundles with pitch-to-diameter ratios of 1.28 and 1.32 and a normal triangular tube bundle with a pitch-to-diameter ratio of 1.32. Comparison of the present fluid-elastic threshold results with previously published data shows good agreement in single-phase flow. The effects of pitch-to-diameter ratio and tube bundle configurations on fluid-elastic instability induced by air-water cross flow were also compared and analyzed by measuring unstable behavior of tube bundles. It was found that fluid-elastic instability is more prone to occur with a decrease of pitch-to-diameter ratio and that the normal square tube bundle is more stable than the normal triangular tube bundle. From the perspective of the tube bundle configurations, it was recommended that the instability constant K in normal triangular and normal square tube bundles be 3.4 and 4.0, respectively.