Abstract

Flow-excited acoustic resonance is a design concern in many industrial applications. For the case of tube bundles in heat exchangers, several acoustic damping criteria were proposed in the literature to predict the occurrence of resonance excitation. However, these criteria are not reliable in differentiating between the resonant and non-resonant cases. A primary reason for that is the geometrical differences between reduced scale models and full-scale tube bundles. Therefore, the effect of two geometrical aspects, namely, the duct height and the cylinder diameter, on the self-excited acoustic resonance is experimentally investigated. Changing the duct height changes the natural frequency of the excited acoustic modes and the acoustic damping of the duct. Changing the cylinder diameter changes the flow velocity at frequency coincidence, and the pressure drop. It is found that increasing the duct height decreases the acoustic impedance, which makes the system more susceptible to resonance excitation. This, in turn, changes the magnitude of the acoustic pressure at resonance, even for cases where the dynamic head of the flow is constant. The acoustic attenuation due to visco-thermal losses is quantified theoretically using Kirchhoff's acoustical damping model. Results from the experiments are compared with the acoustic damping criteria from the literature for similar cases. It is revealed that the height of the duct is an important parameter that should be included in damping criteria for tube bundles, as it controls the acoustic damping of the system, which have been over-looked in the past.

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