Flow-Induced Noise in Heat Exchangers

Flow-induced tonal noise and acoustic resonance problems are found in a variety of applications that range from nuclear power plant heat exchangers to automobile air conditioning evaporators. Flow-induced noise in heat exchangers is a very complex phenomenon. The complexities are caused by several factors that affect the noise generation and attenuation mechanisms of sound sources inside ducts, and by fluid-acoustic-structural coupling effects. To predict the noise from bluff bodies inside a duct, one needs to account for the sound source???s strength and directionality, the damping and sound attenuation mechanisms inside the duct, and the effects produced by the coupling between the acoustic field and the vortex generation process. Flow-induced tonal noise generated in plate heat exchangers has unusual features that have not been previously explored. Measurements of the flow-induced noise produced by plate heat exchangers, arrays of cylinders, cylinders in tandem, side by side cylinders, single cylinders of constant diameter and ???hourglass??? shaped cylinders inside a rectangular duct have been made. The acoustic field in parts of the duct in which traveling hydrodynamic pressure fluctuations produced by vortex shedding do not contaminate the results was investigated by measuring sound pressure levels. Many of the results are believed to be unique. The measurements were then used to infer noise source strength and system damping using an acoustic model. The acoustic model was based on the inhomogeneous convected Helmholtz equation with a point dipole source term, volumetric damping and damping at the duct walls. The acoustic model was able to closely match the measured sound pressure field and the phase relationships between measurement points for sound generated by flow over short aspect ratio single cylinders inside a duct. The acoustic model based technique was also applied to investigate some of the flow-induced noise behavior and trends of side by side cylinders, cylinders in tandem and a staggered cylinder array with many cylinders