New Design Recommendations for Fluidelastic Instability in Heat Exchanger Tube Bundles

Abstract

Abstract The “VDI-Wärmeatlas”, the standard design handbook for heat exchange in Germany, now includes a new guidline for vibration excitation in heat exchanger tube bundles (Gelbe et al. (1997)). Chapter 3 deals with the fluidelastic instability, which is the most important excitation mechanism to be considered when disigning tube bundle heat exchanger. The existing recommendations from Chen (1987), Weaver and Fitzpatrick (1987) and Pettigrew and Taylor (1991) differ in the suggested equations to calculate critical velocities for single phase cross-flow. With an extensive evaluation and test of consistency of these and new available data on this topic, new correlations are derived. Uniform definitions of critical flow velocity for instability, damping, natural frequency and hydrodynamic mass are used; their values are to be determined in still fluid with the density ρ. Confident documented data show only a small scatter. The other data deviate more, but mainly to the safe side. The stability constant is a function of the tube pitch ratio for all tube bundle configurations subjected to liquid or gas cross flow, except for the rotated triangular one. The pitch ratio has the strongest influence for the normal triangular array and the influence becomes less for the rotated as well as the in-line square configuration. This significant influence of the pitch ratio and the tube bundle configuration on the stability constant enables a reasonable interpolation for non-standard configurations. The exponent of the dimensionless mass-damping parameter for gas cross flow depends on the standard tube configuration and is 0,5 for the 30°- and 45°- and 0,45 for the 60°- and 90°-configurations. For liquid flow a uniform exponent of 0,15 has been observed.