New design recommendations for fluidelastic instability in heat exchanger tube bundles

Design equations are presented to determine the critical velocities for the occurrence of fluidelastic instability in uniform single-phase cross-flow. These equations are an essential part of a new guideline in the "VDI-Warme atlas" for estimating vibration excitation in real tube bundle heat exchang ers. Six existing guidelines fbr fluidelastic instability were tested and c ompared with about 300 experimental data from 34 papers (eight of them bein g not yet considered in a guideline before). New equations for the stabilit y factor K as a function of the pitch ratio for different tube configuratio ns were derived with statistical methods by a variation of the reference de finitions for the structural parameters and the exponents of either the dim ensionless mass and the damping or the mass-damping parameter. The criterio n used here was first to be on the safe side with a minimum number, and min imum deviation, of experimental data below the recommended threshold line, and second a minimum r.m.s. error for all data considered. The pitch ratio has the strongest influence for the normal triangular array and the influen ce becomes less for the rotated as well as for the in-line square configura tion. This significant gradation of the stability constants as a function o f the pitch ratio and the tube bundle configuration enables a reasonable in terpolation for non-standard configurations. The exponent of the dimensionl ess mass-damping parameter for gas cross-flow depends on the tube configura tion and is 0.5 for the 30 degrees- and 45 degrees-configuration, and 0.4 f or the 60 degrees- and 90 degrees-configuration. For liquid how, an average exponent of 0.15 hats been observed. (C) 1999 Academic Press.