Reduction of Flow-Induced Noise in Refrigeration Cycles

In electrified vehicles, auxiliary units can be a dominant source of noise, one of which is the refrigerant scroll compressor. Compared to vehicles with combustion engines, e-vehicles require larger refrigerant compressors, as in addition to the interior, also the battery and the electric motors have to be cooled. Currently, scroll compressors are widely used in the automotive industry, which generate one pressure pulse per revolution due to their discontinuous compression principle. This results in speed-dependent pressure fluctuations as well as higher-harmonic pulsations that arise from reflections. These fluctuations spread through the refrigeration cycle and cause the vibration excitation of refrigerant lines and heat exchangers. The sound transmission path in the air conditioning heat exchanger integrated in the dashboard is particularly critical. Various silencer configurations can be used to dampen these pulsations. This paper compares the acoustic and thermodynamic performance of two mufflers and a resonator for different operating points. It is shown that the installation of the various flow silencers has no influence on the thermodynamic efficiency of the refrigeration cycle. Measurements of the pressure pulsations before and after the flow silencer are carried out using a refrigeration cycle acoustic test rig. The experimentally determined transmission loss values are compared with impedance tube measurement results and analytically calculated sound attenuation curves of the mufflers. The three different flow silencers dampen the pressure pulsations in the refrigeration cycle across a wide frequency range. The single-chamber muffler has the highest transmission loss in the low-frequency range up to 200 Hz and attenuates the high-amplitude 1st order pressure pulsations by up to 20 dB. The multi-chamber muffler achieves a transmission loss of up to 30 dB in the higher frequency range from 400 Hz. For both mufflers, there is good agreement between the measured values in the refrigeration cycle, in the impedance tube and the analytically calculated values. For the resonator, the measured transmission loss in the refrigeration cycle is significantly lower than in the impedance tube. The transmission loss of the resonator in the refrigeration cycle is constant at approx. 5 dB up to 600 Hz. The findings on the operation principle and damping performance of different refrigerant cycle silencers enable the reduction of flow-induced noise in thermomanagement system components in vehicles.