Enhancing muffler transmission loss using periodicity

Periodic waveguides exhibit frequency bands where waves are evanescent due to Bragg scattering, i.e., wave cancelling due to multiple out-of-phase reflections. Therefore, such periodic undamped waveguides heavily attenuate incoming waves. Aiming at enhancing the sound transmission loss (STL) of compressor suction mu ers, this work investigates the use of periodic expansion chambers. First, a simple reactive mu er was investigated both numerically and experimentally. The theoretical model was built using an analytical plane wave spectral element method (SEM) and using the finite element method (FEM). A simple reactive mu er consisting of three expansion chambers was 3D-printed and experimentally tested. Simulated results computed with both models presented very similar results. The STL estimated experimentally using the two-load method clearly indicated the predicted bandgaps. Finally, using the validated FEM procedure, a new design of a suction mu er is proposed for application in a commercial compressor to enhance the STL around 6.3 kHz. The designed periodic suction mu er showed an attenuation of approximately 35 dB within the predicted bandgap.