Investigation of Acoustic Resonance Phenomenon in a Large-Scale Heat Exchanger

Abstract

Abstract In gas-gas heat exchangers, pure tone noise can be generated by gas flow pass tube arrays when the frequency of vortex shedding is close to that of acoustic modes, which is called acoustic resonance. Such resonance phenomenon usually occurred while serving because it is difficult to predict in the design stage. The loud noise is harmful to operational staff and may cause structural damage. The paper reports a case of acoustic resonance in a large-scale heat exchanger containing more than 15,000 staggered tubes with a pitch ratio of 1.33. Unexpected acoustic resonance occurs during service although two longitudinal baffles have been installed aiming to eliminate it. The noise of high-pressure levels appears in the heat exchanger operation process. Acceleration signals are obtained at different positions of the outer wall. Results show that acceleration fluctuations are dominated by narrow band peaks from 100 to 145Hz. By numerically investigating the characteristics of the flow field, vortex shedding frequency is found to be similar to this range, indicating a close relationship between vortex shedding and acoustic resonance. The acoustic modes of the shell side are also calculated by using the effective speed of sound. The results show that the modes excited are more likely to be a combination of longitudinal and transverse modes, rather than a transverse mode which is more commonly encountered. Longitudinal modes used to be ignored and staggered tube bundles are considered not prone to suffer acoustic resonance, which may increase the risk in the design stage. From the case discussed in this paper, it is probably necessary to take both longitudinal and transverse coupled modes into consideration.