System noise reduction for chillers

Transmission loss (TL) is perhaps the most useful metric in the design of noise reduction silencers. However, in chiller systems, the use of TL simply to reduce outlet pulsating pressures is not sufficient for system noise reduction. This is especially true when reflection waves and standing waves build up and increase compressor and pipe noises, which can dominate chiller noise sources. In this study: the transmission loss (TL), the reflection coefficient (RC), and the acoustic specific impedance (Z) are applied for the inlet, outlet, and silencer noise reductions. The viscous Lautrec number (the ratio of viscous penetration depth to the hydraulic radius) is critical in determining the best viscous material choice. For oscillating flow, when the Lautrec number is less than 1, the velocity gradient and shear gradient depend only on the pore geometry. Applying this method, a chiller achieved a reduction in system sound power of 25 dB. The compressor shell’s vibrations were reduced to 1/20 and the discharge pulsating pressures to 1/100. Fluid–structure interaction and boundary element method (BEM) were used to model radiation noise, fluid, and structure. The modeling results closely matched experimental data.