Fluidelastic Tube Vibration in a Heat Exchanger Designed for Sodium-to-Air Operation

Analysis and testing were performed to evaluate the potential for flow induced vibrations of the finned U-tubes of a sodium-to-air dump heat exchanger of the Fast Flux Test Facility (FFTF). The analysis showed that fluidelastic vibration of the U-bend sections, caused by a displacement-dependent mechanism, could be experienced. Consequently, model tests, with prototypic tubing and stagnant water simulating the sodium mass on the tubeside, were performed. The tests consisted of subjecting the overhanging U-bends of a bank of five U-tubes to a range of air flow velocities at room temperature. Test results showed that, for a given support and restraint condition, a critical flow velocity exists above which large vibration amplitudes are induced. Characterization of the critical flow velocity was investigated. Supplementary single tube experiments determined vortex shedding frequencies, U-tube natural frequencies, damping, and, separately, the effect of internal water flow.